physics - · pdf filephysics higher and ordinary level ... release mechanism, pressure plate /...

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PRE-LEAVING CERTIFICATE EXAMINATION, 2017

MARKING SCHEME

PHYSICS

HIGHER AND ORDINARY LEVEL

*WMS13*

35 Finglas Business Park, Tolka Valley Road, Finglas, Dublin 11T: 01 808 1494, F: 01 836 2739, E: [email protected], W: www.examcraft.ie

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In considering this marking scheme the following points should be noted:

1. In many instances only key words are given �– words that must appear in the correct context in the candidate�’s answer in order to merit the assigned marks.

2. Words, expressions or statements separated by a solidus, /, are alternatives which are equally acceptable.

3. Answers that are separated by a double solidus, //, are answers which are mutually exclusive. A partial answer from one side of the // may not be taken in conjunction with a partial answer from the other side.

4. The descriptions, methods and de nitions in the scheme are not exhaustive and alternative valid answers are acceptable.

5. The detail required in any answer is determined by the context and manner in which the question is asked and by the number of marks assigned to the answer in the examination paper. Therefore, in any instance, it may vary from year to year.

6. For omission of appropriate units, or incorrect units, one mark is deducted, unless otherwise indicated.

7. Each time an arithmetical slip occurs in a calculation one mark is deducted.

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HIGHER LEVEL Question 1. 40 marks

In an experiment to measure the acceleration due to gravity, the time t for an object to fall from rest through a distance s was measured. The procedure was repeated for a series of values of the distance s. The table shows the recorded data.

s(cm) 30 50 70 90 110 130 150

t(ms) 247 310 377 435 473 514 540

t2 (s2) 0.0610 0.0961 0.1421 0.1892 0.2237 0.2642 0.2916

Draw a labelled diagram of the apparatus used in the experiment.timer, ball, release mechanism, pressure plate / trap door (any two items for 3 marks) (3 + 2 + 1)( �–1 if release mechanism not labelled)

Indicate the distance s on your diagram.(perpendicular) distance indicated between bottom of ball and top of pressure plate (any correct answer) (3)

Describe how the time interval t was measured. (15)timer starts when ball leaves release mechanism (3) timer stops when ball hits pressure plate / trap door / impact switch (3)

Calculate a value for the acceleration due to gravity by drawing a suitable graph based on the data above. (21)at least 6 correct values for t 2 (�–1 per each incorrect value) (3) axes correctly labelled (3) at least 6 points correctly plotted (3) straight line with a good distribution ( �–1 for poor distribution) (3) correct slope method (3) slope = 5.02 // 0.198 ( 0.20) (3) g = (10.04 ± 0.20) m s�–2 (�–1 for omission of or incorrect unit) (3)

Give two ways of minimising the effect of air resistance in the experiment. (4) small (object) / smooth (object) / no draughts / in vacuum / distances relatively short heavy (object) / dense / spherical / aerodynamic (2 + 2)

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Question 2. 40 marks

In an experiment to measure the focal length of a converging lens, a student measured the image distance v for each of four different values of the object distance u.The table shows the data recorded by the student.

u (cm) 6.0 9.0 11.8 15

v (cm) 32.3 11.1 9.0 7.7

Describe, with the aid of a labelled diagram, how the student obtained the data. (10)apparatus: e.g. ray box, convex lens, screen (2) correct arrangement of apparatus (�–1 if screen is not labelled) (2) adjust to get image in sharp focus (2) measure u and v (2) repeat for different positions of object (2)

Give two precautions that should be taken when measuring the image distance. (5)measure from the centre of the lens (to the screen) / measure perpendicular distance / avoid parallax error / check zero error in metre rule (any two precautions) (5)

Using all the data in the table, nd the value for the focal length of the lens. (15)formula (3) derivation of f (3 marks per each correct value for f �– max mark 3 × 3) (3 × 3)average f ( = 5.0 ± 0.2) cm (3)

Why is it dif cult to measure the image distance when the object distance is less than 10 cm? (6)

image is virtual / image on same side as object / no image formed on screen (6)

What is another name for a converging lens? (4)Convex lens (4)

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In an experiment to verify Snell�’s law, a student measured the angle of incidence i and the corresponding angle of refraction r for light entering a material. This was repeated for a number of different angles of incidence.The student then plotted the graph below based on the collected data.

Draw a labelled diagram of the apparatus used.pins / ray box (to obtain incident and refracted rays) (3) diagram to show: outline of block, incident and refracted ray, normal (3) measure angle between refracted ray and normal (using a protractor / trig.) (3)

On your diagram, indicate an angle i and its corresponding angle r. (10)Correct angles shown (1)

What labels should be used, instead of X and Y?X = Sin r, Y = Sin i (5)

What is the smallest angle of incidence that the student set in this experiment? (10)Sin �–1 (0.5) = 30° (5)

Complete the graph above and use the completed graph to determine the refractive index of the material.Correct slope method (5)(n = ) 1.49 [range: 1.45 �– 1.55] (3)

How does the graph verify Snell�’s law? (10)A straight line through the origin shows that sin i is proportional to sin r (2)

What material was probably used in this experiment?Glass that has a refractive index of 1.5 (4)

The student did not record any values of the angle i below 30°. Give two reasons why? (10)To reduce the (percentage) error (3)Elaboration e.g. dif cult to measure / read angles, r < i , etc. (3)

X

Y

y = 1.4856x

0.20.2 0.3 0.4 0.5 0.6 0.7 0.8

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

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In an experiment to investigate how current I varied with voltage V across a copper sulfate solution with copper electrodes, a student collected the following data.

V (V) 0 1 2 3 4 5 6 7 8

I (mA) 0 26 52 79 105 131 157 183 210

Draw a suitable circuit diagram for this investigation and label the components. (8)arrangement: power supply unit, label ammeter, label voltmeter, electrolyte, electrodes (4 × 2) (�–2 marks per missing component)

How was the potential difference changed during the experiment? (8)adjusting (dial / selector on) variable p.s.u. // adjusting rheostat (8)

Draw a suitable graph to show the relationship between the current and the potential difference. (8)label axes correctly on graph paper (2) plot six points correctly (�–1 per each incorrect point; �–1 mark if inappropriate scale) (2) straight line (2) good distribution (2)

Use your graph to calculate the resistance of the solution. (8)method for slope (4) R 38 (�–1 for omission of or incorrect unit) (4)

What was observed at the electrodes as current owed through the solution? (8)cathode got heavier / coated with fresh copper (4) anode got lighter (4)(Any valid observation re anode and cathode, e.g. colour intensity of electrolyte, etc.)

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SECTION B (280 marks)

Answer ve questions from this section. Each question carries 56 marks.

Question 5. 56 marksAnswer any eight of the following parts, (a), (b), (c), etc.(a) A particle travels at a constant speed of 10 m s�–1 in a circle of radius 2 m. What is its angular velocity? = v/r (4) = 10/2 = 5 rad s�–1 (3)

(b) An alternating voltage has a peak value of 75 V. What is the r.m.s. value? Vrms = Vp/ 2 (4) 53 V (3)

(c) State the law of otation. The law of otation states that when a body is wholly or partially immersed in a liquid, it oats if the weight of the liquid displaced is equal to the weight of the body. (4 + 3)

(d) Give one advantage and one disadvantage of using a convex mirror, instead of a plane mirror, as a wing mirror on a car. advantage: wide eld of view / always erect disadvantage: image diminished, image distance reduced compared to actual distance (4 + 3)

(e) How much energy is stored in a 100 F capacitor when it is charged to a potential difference of 12 V? W = ½ C V2 (4) 7.2 mJ (3)

(f) What is point discharge? An electrical discharge from a pointed conductor maintained at a potential that differs from that of the surrounding air. Partial correct (4) fully correct (+3)

(g) What is meant by nuclear ssion? A nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy. Partial correct (4) fully correct (+3)

(h) What is meant by the threshold of hearing? The hearing threshold is the sound level below which a person�’s ear is unable to detect any sound (4 + 3)

(i) What happens when high speed electrons collide with a metal target? X-rays are produced Partial correct (4) fully correct (+3)

(j) Name the sub-atomic particles that are affected by the strong force. Quarks Partial correct (4) fully correct (+3) or An OR gate has two inputs, A and B. In what circumstances will the output of the gate be �‘high�’? When A is high, OR B is high OR when both A and B are high Partial correct (4) fully correct (+3) (8 × 7)

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De ne (i) displacement, (ii) acceleration. (6)Displacement is a vector quantity that refers to �“how far out of place an object is�”; it is the object�’s overall change in positionAcceleration is the rate of change of velocity per unit of time 3 + 3A body is travelling with a velocity u in a certain direction. It then accelerates uniformly in the same direction for a time t. Show that s = ut + ½ at2 where s is the displacement of the body and a is the acceleration. (12)

Distance travelled = area under the line = ut + ½ (v �– u)t (4)But acceleration = (v �– u)/t and so (v-u) = at therefore: (4)Distance travelled (s) = ut + ½ (v-u)t = ut + ½ [at]t = ut + ½ at2 (4)

A car accelerates uniformly from rest to a speed of 20 m s�–1 in a time of 6 s. It then moves at a constant speed until it has reached a total distance of 260 m. Calculate:

(i) the total time taken to travel the distance of 260 m. Total area = 260 m (2) A1 = ½ .6. 20 = 60 m (2) A2 = ? . 20 60 + 20? = 260 (2) ? = 10 s Total time = 6 + 10 = 16 s (2)

(ii) the average speed of the car over the whole journey. (16) Average speed = total distance / total time (4) 260/16 16.25 ms�–1 (4)

Area = ½ (v �– u)t

Area = ut

timet

u

v

velocity

6 s ? s

A1 A2

20 ms�–1

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A parachutist is falling with a vertical velocity of 15 m s�–1 when he is blown by the wind which has a horizontal velocity of 8 m s�–1. Calculate his resultant velocity. (12)

vr = (82 + 152) (6)= 17ms�–1 (6)

At a certain time before landing the parachutist is directly over a point X painted on the ground. The parachutist lands 10 s later. What distance from the X has he landed? (10)Component of velocity in x-direction = 8 m�–1 (5)After 10 seconds he has travelled 10 × 8 = 80 m (5)

8 ms�–1

15 ms�–1

17 ms�–1

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Explain the term resonance and describe a laboratory experiment to demonstrate it. (15)transfer of energy (state / imply) (3) so that a body vibrates at its natural frequency (3) apparatus: tuning fork, length of pipe (with means of varying length) (3) procedure: hold vibrating fork over (open) end of pipe and vary length (of air column) (3) observation: loud sound is heard (at certain length) (3)

A set of pan pipes is made from different lengths of tubing that are open at both ends. When the musician blows, the pipes emit sounds.The sound from one of the tubes was analysed and the following frequencies were identi ed in the sound: 550 Hz, 1100 Hz and 1651 Hz.What name is given to this set of frequencies? (5)overtones / harmonics (5)

Draw labelled diagrams to show how the tube produces each of these frequencies.550 Hz (f): antinodes (A) at both ends (2) linked correctly to one node (N) (in the centre) (2) 1100 Hz (2f): antinodes at both ends (2) linked correctly to two nodes (2) 1651 Hz (3f): antinodes at both ends linked correctly to three nodes (2) ( �–1 if no correct label)

The length of the analysed tube is 30 cm. Use any of the above frequencies to calculate a value for the speed of sound in air. (20)c = f (4) = 0.60 m (3)

c 550 × 0.60 = 330 m s 1 (�–1 for omission of or incorrect units) (3)

Another musician uses a sample of wire, of length 12 m and mass 48 g, as a guitar string. A 64 cm length of the wire was xed at both ends and plucked. The fundamental frequency of the sound produced was found to be 173 Hz. Calculate the tension in the wire. (12)

= 0.048 ÷ 12 = 0.004 kg m 1 (3) f = 1/2l (T / ) (3) T = 4(lf)2 (3) T [= 4 × (0.64 × 173)2 × 0.004] = 196 N (�–1 for omission of or incorrect units) (3)

Explain why a musical tune does not sound the same when played on different instruments. (4)

different instruments emit (a fundamental frequency plus) different (combinations of) overtones / harmonics (4) (�‘a closed pipe emits odd multiples of a fundamental frequency whereas an open pipe emits all multiples of the fundamental�’)

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What is an electric current? (4)An electric current is a ow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire Partially correct (3), fully (4)

Heating is one effect of an electric current. Give two other effects of an electric current. (12)Chemical: Passing an electric current through a liquid causes chemical changes in a process called electrolysisMagnetic: Electric current passing through a wire generates a magnetic eld around the wire (6 + 6)

The diagram shows a basic electrical circuit of an everyday household device. When an electric current ows through the coil of wire, the air around it heats up and the motorised fan blows.

(a) Describe what happens: (i) when switch A is closed and the rheostat is adjusted fan operates and its speed (of rotation) changes (3) (ii) when switch A and switch B are closed. (9) charge / current ows through coil // coil gets hot (3) fan blows hot air (3)

(b) The maximum power generated in the heating coil is 1 kW. (i) What is the initial resistance of the coil? (ii) Calculate the current that ows through the coil when the circuit is turned on. (9) P = IV (3) (ii) I = P/V = 1000 / 230 = 4.35 A (3) (�–1 for omission of or incorrect units) (i) V = RI, R = 230 / 4.35 = 52.9 (3) (�–1 for omission of or incorrect units)

(c) A length of nichrome wire of diameter 0.20 mm is used for the coil. Calculate the length of the coil of wire. (18) A = r2 (3) = 3.14 (0.0001)2 (3) A = 3.1 × 10�–8 m2 (3) = RA / l (3) l = 52.9 . 3.1 × 10�–8 / 1.1 × 10�–6 (3) l = 1.49 m (3)

(d) What everyday household device could this be? (4) Hairdryer / hot air blower (4) (resistivity of nichrome = 1.1 × 10�–6 m )

fuse

fan

coil

B

A

230 V

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State Coulomb�’s law. (6)Coulomb�’s law states that: The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them. (2 + 2 + 2)

A solid conductor in the shape of a sphere carries a positive charge. Draw the sphere and indicate how the charge is distributed over the surface of the sphere. (6)

(3 + 3)

De ne the term electric eld intensity, E, and give its unit. (7)An electric eld is a vector eld that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an in nitesimal test charge at that point (4)newtons per coulomb (N · C 1) (3)

Two identical spherical conductors on insulated stands are placed a certain distance apart. One conductor is given a charge Q while the other conductor is given a charge 3Q and they experience a force of repulsion F. The two conductors are then touched off each other and returned to their original positions. What is the new force, in terms of F, between the spherical conductors? (16) (4) (4) (4) (4)

Calculate the force of repulsion between the two small spheres in the gure below when they are held 8 cm apart in a vacuum. Each sphere has a positive charge of +3 C. (9) (3)

= 8.99 × 109 × (3 × 10 6 C × 3 × 10 6 C) / (0.082) (3)= 12.65 N (3)

Copy the diagram above and show on it the electric eld generated by the charges.Accurate diagram of the electric elds (6)

Mark on your diagram a place where the electric eld strength is zero. (12)Electric eld is zero at the midpoint between the charges (6)

+ ++

+++

+++++

+++

+ +

+3 C +3 C8 cm

( )FF

Fdd

F

dQ

dQQ

hF

dQF

dQQF

=

=

==

=

=

34'

34

44'

441221'

4141

2

2

22

2

23

221

!!

!!

!

!

= 221

41

dQQF

!

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Answer either part (a) or part (b).

(a) List three quantities that are conserved in nuclear reactions. (6) momentum, charge, mass-energy, nucleons, etc. (any three valid answers) (2 + 2 + 2)

Write an equation for a nucleus undergoing beta-decay.

(3 + 3 + 3)

In initial observations of beta-decay, not all three quantities appear to be conserved. What was the solution to this contradiction? (12) proposal / discovery of the neutrino (3)

List the fundamental forces of nature in increasing order of their strength. gravitational < weak (nuclear) < electromagnetic < (strong) nuclear (3 × 3) (3 marks for naming any two; 2 × 3 marks for naming the correct four; 3 marks for correct order)

Which fundamental force of nature is involved in beta-decay? (12) weak (nuclear) (3)

In the Large Hadron Collider, two protons with the same energy and travelling in opposite directions collide. Two protons and two charged pi mesons are produced in the collision.

Why are new particles produced in the collision? energy is converted into mass / E = mc2 (3)

Write an equation to represent the collision. (12)

p + p p + p + + + �– (3 × 3)

Show that the kinetic energy of each incident proton must be at least 140 MeV for the collision to occur. (14) Mass of + = 273 me (4) E = mc2 (3) E = 279.94 × 106 eV ~ 280(MeV) (4) Therefore energy per proton = 140 MeV (3)

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(b) State one law of electromagnetic induction. (6)

The Laws of Electromagnetic Induction.Faraday�’s Law states that the size of the induced emf is proportional to the rate of change of ux. Lenz�’s Law states that the direction of the induced emf is always such as to oppose the change producing it One fully correct (6)

Draw a labelled diagram of an induction coil and explain how it works. (20)p

Diagram showing primary coil, secondary coil, iron core, power supply and spark gap (5 × 2)Two coils of insulated copper wire wound around a common iron core. One coil, called the primary winding (P), is made from relatively few turns of coarse wire. The other coil, the secondary winding, (S) typically consists of many thousands turns of ne wire.An electric current is passed through the primary, creating a magnetic eld. The primary behaves as an inductor, storing energy in the associated magnetic eld. When the primary current is suddenly interrupted, the magnetic eld rapidly collapses. This causes a high voltage pulse to be developed across the secondary terminals through electromagnetic induction. This voltage is often suf cient to cause an electric spark, to jump across an air gap (G) separating the secondary�’s output terminalsCorrect explanation of the 5 components (5 × 2)

De ne magnetic ux, . (6)Magnetic ux is the product of the average magnetic eld times the perpendicular area that it penetrates. (3)

= BA (3)

A at circular coil of radius 1.6 cm and consisting of 80 turns of wire lies in a plane which is perpendicular to a magnetic eld of magnetic ux density 0.20 T. Calculate the magnitude of the induced e.m.f. when the ux density is steadily reduced to zero in 0.50 s. (12)

= NBA Cos (4)A = r2 = 0.008 m (2)

= BA = 0.2 × 0.008 = 0.0016 Wb (2)E = N( / t) = 80 × (0.0016/0.5) (2)= 0.0256 V (2)

Explain the principle involved when a small metal cylinder is dropped through one end of the copper tube, it falls freely under gravity. If the small cylinder is rst magnetised, it then takes much longer to fall through the tube. (12)Magnetic elds are the result of electric currents. Changing a magnetic eld (moving a magnet) next to a non-magnetic metal will induce an electric eld (a voltage difference) in the metal, which subsequently generates a magnetic eld with an opposite orientation with respect to the magnet. This phenomenon is known as Lenz�’s Law (4 × 3)

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Tiny laser makes �‘twisted light�’A tiny laser that emits �“twisted light�” has been unveiled by scientists in the US and Italy. Measuring just 9 m across, the semiconductor device can produce a beam of light that carries an angular velocity. While improvements are needed before the laser can be commercialized, it could someday be used to boost the capacity of existing telecommunication systems. In a beam of light with an angular velocity, the wavefront twists around the direction of propagation, creating a vortex in the middle of the light beam.Now, scientists at the State University of New York and the Polytechnic University of Milan have created a tiny laser that comprises a ring of semiconductor material with outer and inner diameters of just 9 m and 7 m, respectively. The ring is about 1.5 m tall and sits on a semiconductor substrate. The top surface of the ring resembles a clock face with �“tick�” marks at regular intervals.This structure is known as a �“microring�” �– and it is well known that laser light will circulate within such a ring when the device is �“pumped�” using an external laser. In a normal microring, however, the light will circulate in both clockwise and anticlockwise directions, and so effectively cancel each other out.This is where the clock-face pattern comes in. The materials used to create the pattern are chosen to have speci c indices of refraction such that light can only ow in one direction. The laser produces light in the infrared range.physicsworld.com

(a) This tiny laser measures 9 m across. What does the symbol represent in scienti c notation?

Micro- is a unit pre x in the metric system denoting a factor of 10 6 (one millionth) 4 + 3(b) The laser is described as a semiconductor device. What is a semiconductor? a substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. 4 + 3(c) What are the charge carriers in semiconductors? in n-type semiconductors they are holes, while in p-type semiconductors they are electrons 4 + 3(d) De ne angular velocity. the rate of change of angular position of a rotating body 4 + 3

(e) In a normal microring, the light circulates in both clockwise and anticlockwise directions, and cancels itself out. What term is given to this interaction? Interference; a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude 4 + 3

(f) What two conditions are necessary for the light to completely cancel itself out? coherent and in phase with each other 4 + 3

(g) The light from this device is in the infrared range. Does light in the infrared range have longer or shorter wavelength compared to visible light?

red has the longest wavelength of visible light, at around 700 nanometers, infrared is greater than this again 4 + 3

(h) Does light in the infrared range have higher or lower frequency compared to visible light?

c=f c is constant, therefore if is larger, f must be smaller 4 + 3

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(a) Conduction, convection and radiation are three methods of heat transfer. Give an explanation of each. (12) Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole (4) Convection is heat transfer by mass motion of a uid such as air or water when the heated uid is caused to move away from the source of heat, carrying energy with it (4) Radiation is heat transfer through the emission of energy as electromagnetic waves (4)

Explain the principle involved in each of the following:

(i) The u-value of a structure is reduced by adding insulation to it. (4) U-value refers to Unit Heat Loss Rate. A good insulating structure therefore has a low U-value Any valid answer, (4)

(ii) On a hot day, the sea is usually colder than the land. (4) Large bodies of water like oceans have higher thermal capacities than land due to their immense density. As a result, it takes up to four times the amount of heat to raise the temperature of a given amount of water 1oC as it takes to raise the temperature of the same amount of land by an equivalent degree. Any valid answer, (4)

(iii) The human body is cooled by perspiring. (4) Sweat uses evaporative cooling to maintain body temperature. The liquid changes into a gas, drawing heat from the liquid. The process draws heat from the body. Any valid answer, (4)

(iv) On a hot day, the water on the surface of a still lake or pond is usually warmer than the water some distance below the surface. (4) Conduction is poor Convection currents go up not down Warm water is less dense and does not sink Any valid answer, 4

(b) What is the photoelectric effect? (6) emission of electrons from the surface of a metal (3) when light of suitable frequency / energy shines on it (3)

Write down an expression for Einstein�’s photoelectric law. (9) hf = + ½mv2 (each incorrect item �– 3) 3×3

Summarise Einstein�’s explanation of the photoelectric effect (9) photons (of light) / quanta / packets (or bundles) of energy (3) all of energy from one photon is given to one electron (3) energy must be greater than work function of metal for P.E.E. to occur / for electron to escape (3) Give one application of the photoelectric effect. (4) soundtrack in lm, photography, counters, photocell, burglar alarm, automatic doors, etc. (4)

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(c) What is a semiconductor diode? (6) A device which allows current to ow // p-type n-type (3) In only one direction // in contact (3)

Draw a diagram of a circuit that could be used to show the operation of a photodiode. (6) Symbols for photodiode and cell (2) Circuit with reverse bias on diode (2) Microammeter / miliammeter / galvanometer (2)

An alternating current of very low frequency (e.g. 1 Hz) is supplied to a light-emitting diode. Draw a suitable circuit diagram for this arrangement. (6) Signal generator and LED in working circuit (6)

What is observed while the current is switched on? Explain your answer. (10) Light goes on and off / ashes (3) ac reverses polarity (1) In forward bias the light is on (3) In reverse bias the light is off (3)

(d) State Newton�’s second law of motion. (6) The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. (3) F = ma (3)

The equation F = �– ks, where k is a constant, describes a law that governs the motion of a body. Name this law and give its de nition. (8) Hooke�’s (4) restoring force (= to k times) // Extension (2) displacement // force / load / weight (2)

Give the name for this type of motion and describe the motion. (8) simple harmonic / SHM (4) a = 2s // acceleration is to (2) explain // displacement / distance (and direction) (2)

A mass at the end of a spring is an example of a system that obeys this law. Give two other examples of systems that obey this law. (6) stretched elastic / pendulum, oscillating magnet, springs of car, vibrating tuning fork, object bobbing in water waves, ball in saucer, etc. or any system that obeys Hooke�’s law any two, (2 × 3)

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ORDINARY LEVELSECTION A (120 marks)

Answer three questions from this section.Each question carries 40 marks.


A student carried out an experiment to measure g, the acceleration due to gravity.

(i) Draw a labelled diagram of the apparatus used. (12) labelled diagram to show: falling object; ball // pendulum bob // picket fence (6) timer; timer shown in diagram // stop-watch // photogate (and timer) (3) detail;stop / start mechanism // xed point/split cork // calculator/computer (3)

(ii) State the measurements taken during the experiment. (6) distance // length (of pendulum) // selected v/s versus t (3) time //period (of pendulum) // slope of graph /t (3)

(iii) Describe how the student took these measurements. (9) 1st correct instrument (6) 2nd correct instrument (3)

(iv) How was a value for g calculated from the measurements? (9) substitute (for t and s) into the relevant equation

// / (3 × 3)

(one error in the equation; 2 × 3) partial answer e.g. substitute into the equation / draw a graph (of T2 versus l) (3)

(v) Give one precaution taken to get an accurate result. (4) any valid speci c precaution, which has not already been awarded marks e.g. use the smallest time value recorded for t* // swing through small angle (4) any valid general precaution e.g. repeat the experiment a number of times (2)

* associated with the problem that the electromagnet will not lose its magnetism immediately, therefore the ball will not fall straight away. This means that the reading on the timer will always be (slightly) longer than the time for which the ball was dropping.

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A student carried out an experiment to measure the speci c latent heat of fusion of ice.The following is an extract from his report.�“In my experiment, I got ice which was at 0 °C and I added it to warm water in a calorimeter. I waited for all the ice to melt before taking more measurements. I used my measurements to calculate the speci c latent heat of fusion of ice.�”

(i) Draw a labelled diagram of the apparatus used in the experiment. (10) labelled diagram to show: calorimeter (3) thermometer // temperature sensor (3) ice (3) insulation / (electronic) balance / stirrer /other detail (1) incorrect experiment, maximum mark (3 × 3) No labels, deduct (2)

(ii) What measurements would the student have taken for this experiment? (6) mass of calorimeter mass of calorimeter and warm water mass of calorimeter and warm water and ice temperature of water before temperature of water and melted ice after any 3 lines (3 × 2) any line (3) mass and temperature (4)

(iii) How did the student prepare the ice for the experiment? (6) crushed / dried / melting ice used any one correct (6) preparation may be inferred from the diagram partial answer; e.g. in the fridge (3)

(iv) How did the student know the ice was at 0°C? (6) (use) melting (ice) / leave ice at room temperature / take its temperature (6) partial answer; (3)

(v) Why did the student use warm water in the experiment? (6) ice melts quickly / less heat loss / increase accuracy / heat lost balanced by heat gained (6) partial answer; e.g. so that the ice would melt (3)

(vi) Why was the experiment repeated? (6) Increase accuracy, reduce experimental error (6)

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A student carried out an experiment to verify Snell�’s law of refraction by measuring the angle of incidence i and the angle of refraction r for a ray of light entering a glass block. The student repeated this procedure two more times. The data recorded by the student is shown in the table.

(i) Draw a labelled diagram of the apparatus used in the experiment. (12) labelled diagram to show glass block (6) pins / raybox (3) protractor / sheet of paper / detail (3) incorrect experiment, maximum mark (6 + 3)

(ii) Describe how the student found the position of the refracted ray. (9) draw the incident ray / mark the point of incidence (3) draw the emerging ray / mark the point of exit (3) join (3) a diagram could merit full marks

(iii) How did the student measure the angle of refraction? (4) using a protractor // by measuring the angle between the normal and the refracted ray (4) partial answer e.g. identi es the angle of refraction (2)

(iv) Copy this table and complete it in your answer book. (9)

angle of incidence i

angle of refraction r sin i sin r sin i / sin r

30° 19° 0.50 0.33 1.52

55° 33° 0.82 0.55 1.49

70° 40° 0.94 0.64 1.47

any correct row // any correct column (6) other correct rows // other correct columns (3)

(v) Use the data to verify Snell�’s law of refraction. (6)

sin i sin r // sin isin r = constant (2 × 3)

partial answer e.g. i r (3)

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In an experiment to investigate how current varied with voltage across a solution, a student collected the following data.

V (V) 0 1 2 3 4 5 6 7 8

I (A) 0 0.3 0.6 0.8 1.2 1.3 1.6 1.8 2.1

Draw a suitable diagram for this experiment and label the components. (12)arrangement: power supply unit, label ammeter, label voltmeter, electrolyte, electrodes (3 × 4)

How was the potential difference measured in the experiment? (6)adjusting (dial / selector on) variable p.s.u. // adjusting rheostat (6)

Using the data in the table, draw a graph on graph paper to show the variation of current with potential difference. (10)label axes correctly on graph paper (3)plot six points correctly (�–1 per each incorrect point) (3)straight line (3)good distribution (1)

Calculate the slope of your graph. (6)method for slope (6)

Use this value to determine the resistance of the solution. (6)R ~ 3.5 �– 4 (�–1 for omission of or incorrect unit) (6)

00

2

4

6

8

10

1 2

y = 3.7561x

3I(A)

V(V) Series 1

Linear(Series 1)

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SECTION B (280 Marks)Five questions to be answered

Question 5. any eight parts 56 marks

Answer any eight of the following parts (a), (b), (c), etc.

(a) State the principle of conservation of momentum. momentum before = momentum after // m1 u1 + m2u2 = m1 v1 + m2v2 (total) momentum is conserved (7) partial answer e.g. incomplete equation, in a closed system (4) (b) A car accelerates from 10 m s 1 to 30 m s 1 in 5 seconds. What is its acceleration? (v = u + at). v �– u / t = 30 �– 10 / 5 = 20/5 = 4 ms�–2 (partial answer 4) (7)

(c) Which one of the following is the unit of power? joule kelvin kilogram watt watt (7) joule (4)

(d) Name one method by which heat can be transferred. Conduction, convection or radiation (partial answer 4) (7)

(e) Name a pair of complementary colours. red�–cyan, green�–magenta or blue�–yellow (partial answer 4) (7)

(f) Infrared radiation is part of the electromagnetic spectrum. Name two other radiations that are part of the electromagnetic spectrum. radiowaves, microwaves / radar, infrared, (visible) light, ultraviolet, gamma rays, X-rays any two (7) any one of the above or any named light colour (4)

(g) Name the electrical component represented in the diagram.

variable resistor (partial answer 4) (7)

(h) List two safety devices that are used in household electric circuits. fuse, trip switch / miniature circuit breaker / MCB, residual current device / RCD, earthing, bonding, etc. any two (7)

any one (4)(i) What is the photoelectric effect? (emission of) electrons from the surface of a metal due to light / radiation (7) partial answer (4) (j) Name a material used as shielding in a nuclear reactor. Lead // concrete (7) partial answer e.g. metal (4)

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De ne pressure. (6)force / F (2) per / divided by (2) unit area / A (2) (N m�–2 / Pascal / Pa, bar, etc.) (2)

Describe an experiment to show that the atmosphere exerts pressure. (9)apparatus: can (containing water) // can (of air) // glass of water (2) procedure: boil water in can // pump // cardboard / lid (2) seal / invert in cold water // air out // invert (2) observation/conclusion: can crushes / collapses // lid supported (3) labelled diagram may merit marks accept valid alternatives

The earth is covered with a layer of air called the atmosphere. What holds this layer of air close to the earth? (6)gravity / gravitational force / weight (6) partial answer e.g. mass (3)

The type of weather we get depends on the atmospheric pressure. Describe the kind of weather we get when the atmospheric pressure is high. (6)dry, good, clear skies, little wind, settled / calm, etc. any one (6) partial answer (3)

A man and a woman are walking together on soft ground. The man has a mass of 80 kg and is wearing at shoes that have an area of 0.05 m2 in contact with the ground. The woman has a smaller mass of 60 kg and is wearing high heels that have an area of 0.02 m2 in contact with the ground.

(i) Find the weight of the man and the woman. (9) W=mg (3) Wman = 80 × 9.8 = 784 N (3) Wwoman = 60 × 9.8 = 588 N (3)

(ii) Calculate the pressure exerted by the woman on the ground. (6) P = F/A (3) Pwoman = 588 / 0.02 = 29400 Pa (3)

(iii) Calculate the pressure exerted by the man on the ground. (3) Pman = 784 / 0.05 = 15680 Pa (3)

(iv) Why is the woman more likely than the man to sink in the soft ground? (5) area / A (3) less / smaller (2) partial answer (3)

(v) Calculate the pressure exerted by the man if he carried the woman across the soft ground. (6) Wt = 1372 N (3) Pt = 1372 / 0.05 = 27440 Pa (3)

g = 9.8 ms�–2

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The diagram shows a waveform.

(i) What is the name given to the distance (a) X, (b) Y? (6) X = Wavelength / (3) Y = Amplitude / height / depth / trough (3) partial mark if both correct but reversed (3)

(ii) How many wavelengths are shown in the diagram? (6) 2 ½ (6)

(iii) What is meant by the frequency of a wave? (6) number of waves (passing a point) per second (6) partial answer (3)

(iv) Explain the term natural frequency? (6) frequency objects tends to vibrate at (when set in motion) // resonance frequency (6) partial answer e.g. lowest frequency (3)

(v) If the natural frequency of a vibrating string is 250 Hz, calculate the wavelength of the sound produced. (9) 1.36 (m) (3 × 3) 340 = 250 × (2 × 3) partial answer e.g. one quantity substituted correctly into the equation / (3)

(vi) State the wave property on which (a) the loudness, (b) the pitch, of a musical note depends. (9) (loudness depends on) amplitude / energy // frequency (pitch depends on ) frequency / wavelength two correct (3 × 3) one correct (2 × 3) partial answer e.g. other property (3) Resonance can occur between objects of the same natural frequency.

(vii) Describe a laboratory experiment to demonstrate resonance. (14) apparatus: Barton�’s pendulums // tuning fork and adjustable length of air (3) procedure: hang the pendulums (vertically) from a horizontal string // hold the vibrating tuning fork near air column (3) set one of the pendulums swinging // adjust the length of the air column (3) observation: the pendulum of the same length also swings // at a certain length the note emitted by the tuning fork gets louder (3) conclusion: a transfer of energy occurs / resonance occurs (2) (c = f , speed of sound in air = 340 m s 1)

X

Y

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(i) State Ohm�’s Law. (9) voltage / pd / V (3) proportional to / / = R (3) current / I (3) partial answer e.g. when the temperature is kept constant (3) The graphs show how current (I) varies with potential difference (V) for (a) a metal, (b) a lament bulb.

Which conductor obeys Ohm�’s law? Explain your answer. (12) graph (a) / metal (6) straight line (3) through origin // shows proportionality (3)

Another type of conductor is a semiconductor. What is a semiconductor? (7) a substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects (partial answer 4) (7)

The circuit diagram shows a resistor and a thermistor connected in series with a 6 V battery. At a certain temperature the resistance of the thermistor is 450 .

(ii) What is the total resistance of the circuit? (7) R1 + R2 = Rt (4) Rt = 500 (3)

(iii) What is the current in the circuit? (7) V = IR 6 = 500 × I; I = 6/500 = (4) 12 mA (3)

(iv) What is the potential difference across the 50 resistor? (7) V = IR V = 12mA × 50 = (4) 0.6 V (3)

(v) What would happen to the resistance of the circuit if the temperature were increased? (7) decreases / increases (7) partial answer e.g. varies, indication of change in resistance (4)

I

V

I

V

(a) a metal (b) a lament bulb

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A magnetic eld exists in the vicinity of a magnet. What is a magnetic eld? (6)region ( where) / space (3) magnetism is experienced // force is detected (3) partial answer e.g. incomplete diagram (3)

Draw a sketch of the magnetic eld around a bar magnet. (9)g

diagram to show magnet, eld lines (6)and correct direction (3) partial answer (6)

Describe an experiment to show that a current carrying conductor in a magnetic eld experiences a force.apparatus: power supply/ battery / voltage, conductor, magnet any two (2 × 3)any one (3) procedure: set up the circuit / turn on the power supply / current (3) observation / conclusion: conductor moves / conductor de ects (3) accept valid alternatives a labelled diagram may merit marks

List two factors that affect the size of the force on the conductor. (18)current / I, strength of magnetic eld / B, length of conductor / l, angle / any two (2 × 3) any one (3)

A coil of wire is connected to a sensitive galvanometer as shown in the diagram. What is observed when the magnet is moved towards the coil? (6)needle / pointer / galvanometer // current (3) de ects // induced (3) partial answer e.g. unquali ed reference to force (3)

Explain why this occurs. (6)emf / voltage / current / electromagnetic induction (3) due to changing magnetic eld (around the coil) (3) partial answer (3)

Describe what happens when the speed of the magnet is increased. (6)greater de ection / emf // current is greater (6)partial answer (3)

Give one application of this effect. (5) dynamo, generator, induction motor, induction cooker, etc. any one (5)

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Nuclear energy can be produced by nuclear fusion and nuclear ssion. Nuclear fusion releases the energy that causes all stars, including our Sun, to exist for billions of years. Nuclear ssion releases the energy that is produced in nuclear reactors in many countries throughout the world.

(i) What is the difference between nuclear fusion and nuclear ssion? (6) Fission is the splitting of a nucleus into (two) smaller nuclei / with release of energy / release of neutrons (3) Fusion is the joining of two nuclei with the release of energy / release of neutrons (3) partial answer; e.g. de nition of fusion (3) Nuclear ssion occurs in a nuclear reactor.

(ii) What is the role of neutrons in nuclear ssion? (6) split nucleus, makes nucleus unstable, causes ssion one correct (6) partial answer; e.g. neutrons red at / hit nucleus (3)

(iii) Name a fuel used in a nuclear reactor. (6) plutonium / P, (enriched) uranium / U, thorium / Th one correct (6) partial answer; e.g. named reactor part (3)

(iv) In a nuclear reactor, how can the ssion be controlled or stopped? (6) correct reference to (control/boron) rods // refers to slowing down neutrons (6) partial answer (3)

(v) How is the energy produced in a nuclear reactor used to generate electricity? (6) (energy produced) converted to heat / (this is used to) generates steam (which) drives generator / turbine (6) partial answer (3)

(vi) Give one advantage and one disadvantage of a nuclear reactor as a source of energy. (6) advantage; abundant fuel / cheap fuel / no greenhouse gases / no global warming, etc. disadvantage; risk of nuclear contamination / fallout / dif culty of dealing with waste / dangerous, etc. advantage and disadvantage for ssion or fusion reactor both correct (6) advantage and disadvantage one correct (3)

(vii) What is the role of (a) the control rods and (b) the moderator in a nuclear reactor? (8) (a) control rods control the rate of ssion, or stop the reaction completely (4) (b) to slow down neutrons / so as to increase the probability of ssion (4) Na 25 is a radioactive isotope of sodium. It has a half- life of 1 minute.

(ix) Explain the term half-life. (6) time taken (3) for half (radioactive) nuclei / element / substance / atoms to decay // activity to half (3)

(x) What fraction of a sample of Na 25 remains after 3 minutes? (6) 1/8 (6) p artial answer e.g. indication of 3 half-lives (3)

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Li-Fi has just been tested in the real world, and it�’s 100 times faster than Wi-FiExpect to hear a whole lot more about Li-Fi - a wireless technology that transmits high-speed data using visible light. Li-Fi and Wi-Fi are quite similar as both transmit data electromagnetically. However, Wi-Fi uses radio waves while Li-Fi runs on visible light. With scientists achieving speeds of 224 Gbits per second in the lab using Li-Fi earlier this year, the potential for this technology to change everything about the way we use the Internet is huge.And now, scientists have taken Li-Fi out of the lab for the rst time, trialling it in of ces and industrial environments in Estonia, reporting that they can achieve data transmission at 1 GB per second - that�’s 100 times faster than current average Wi-Fi speeds.Li-Fi was invented by Harald Haas from the University of Edinburgh, Scotland back in 2011, when he demonstrated for the rst time that by ickering the light from a single LED, he could transmit far more data than a cellular tower. Think back to that lab-based record of 224 gigabits per second - that�’s 18 movies of 1.5 GB each being downloaded every single second.The technology uses visible light of around 500 terahertz (THz). It works basically like an incredibly advanced form of Morse code - just like switching a torch on and off according to a certain pattern can relay a secret message, icking an LED on and off at extreme speeds can be used to write and transmit things in binary code. And while you might be worried about how all that ickering in an of ce environment would drive you crazy, don�’t worry - we�’re talking LEDs that can be switched on and off at speeds imperceptible to the naked eye. The bene ts of Li-Fi over Wi-Fi, other than potentially much faster speeds, is that because light cannot pass through walls, it makes it a whole lot more secure.(Adapted from physicsworld.com)

(a) What is Li-Fi? Li-Fi is using visible light to transmit data electromagnetically Fully correct (7), partially correct (4)(b) What is the difference between Li-Fi and Wi-Fi? Wi-Fi uses radio waves while Li-Fi runs on visible light Fully correct (7), partially correct (4)

(c) In Estonia, they could achieve data transmission at 1 GB per second. What does �‘G�’ represent in Scienti c Notation? G stands for giga, 109 Fully correct (7), partially correct (4)

(d) Li-Fi was demonstrated by ickering the light from an LED to transmit data. What is an LED? Light Emitting Diode Fully correct (7), partially correct (4)

(e) Name a material used as a semiconductor. Silicon, Germanium or gallium arsenide Fully correct (7), partially correct (4)

(f) Using Li-Fi, 18 movies could be downloaded every single second. How many movies could be downloaded in one hour? 18 × 60 × 60 = 64800 Fully correct (7), partially correct (4)

(g) Visible light has a frequency, f of around 500 × 1012 Hz. If visible light has a velocity of 3 × 108 m s-1, what is its wavelength, ? (c = f ) 3 × 108 = 500 × 1012 × = 600 nm Fully correct (7), partially correct (4)

(h) State one advantage and one disadvantage of Li-Fi compared to Wi-Fi one advantage is Li-Fi is faster than current average Wi-Fi speeds light cannot pass through walls, therefore Li-Fi is a whole lot more secure Fully correct (7), partially correct (4)

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Question 12. Answer any two of the following parts (a), (b), (c), (d). 2 × 28

(a) The pressure exerted on any object underwater varies with depth.

(i) State Boyle�’s law. (9) P 1/V // PV = constant (6) for a xed mass of gas at constant temperature (3)

(ii) How does Boyle�’s law explain why a bubble gets bigger as it rises towards the surface of a lake? (9) Fixed mass of gas, as the pressure reduces as it rises towards the surface, the volume increases (9)

(iii) A sh starts at a depth of 20 m in water and rises to 1 m below the surface. What is the change in pressure on the sh as it makes this rise? (10) pressure at bottom due to water = P = h g= 20 × 9.8 × 1000 = 196,000 Pa (4) pressure 1m below the surface = P = h g= 1 × 9.8 × 1000 = 9,800 Pa (4) Difference = 18,6200 Pa (2) (density of water = 1000 kg m�–3; acceleration due to gravity, g = 9.8 m s�–2)

(b) Loudness, pitch and quality are characteristics of a musical note. Name the physical property of a sound wave on which each characteristic depends. (12) loudness depends on amplitude / frequency pitch depends on frequency quality depends on overtones / harmonics three correct (6 + 2 × 3) two correct (6 + 3) any one correct (6)

A bat detector allows us to hear the sounds emitted by bats. The detector is needed as humans cannot hear the sounds as they are outside our frequency limits of audibility.

(i) What is meant by the frequency limits of audibility? (6) are the lowest and highest frequencies which humans can hear // range of frequencies which we can hear // 20 �– 20 000 Hz (6) partial answer e.g. incomplete statement / 20 Hz (3)

(ii) What name is given to a sound whose frequency is greater than our upper frequency limit of audibility? (4) ultrasonic (4) partial answer e.g. incomplete statement / supersonic (2)

(iii) A bat emitted a sound wave and detected its re ection from a wall 0.02 s later. Calculate the distance of the bat from the wall. (6) 3.4 (m) (6) partial answer e.g. correct equation (3) (speed of sound in air = 340 m s 1)

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(c) In an experiment to demonstrate the photoelectric effect, a piece of zinc is placed on a gold leaf electroscope, as shown. The zinc is given a negative charge causing the gold leaf to de ect.

Explain why the gold leaf de ects when the zinc is given a negative charge. (9) like charges / electrons repel two correct (6 + 3) one correct (6) partial answer (3)

Ultraviolet radiation is then shone on the charged zinc and the gold leaf falls. Explain why. (9) electrons / charge (3) (are) emitted from (3) zinc / metal (cap) / leaf (3) partial answer (3)

What is observed when the experiment is repeated using infrared radiation? (6) leaf does not collapse / nothing changed (6) partial answer e.g. nothing (3)

Give one application of the photoelectric effect. (4) photocell / burglar alarms / smoke alarms / automatic doors / machine safety switches etc. (4)

(d) What is electromagnetic induction? (10) emf / voltage / potential difference / current is induced (due to) changing (magnetic) ux / eld // moving magnet two lines correct (6 + 4) one line correct (6) a diagram or example may merit full marks

The diagram shows a transformer. (i) Name the parts labelled A and B. (6) A = soft iron / core / (laminated) iron / former (3) B = primary / input / coil (3)

(ii) The input voltage is 230 V. Part B has 4600 turns and part C has 120 turns. Calculate the output voltage. (6) Vo = (230 × 120) / 4600 = 6(V) (6) partial answer e.g. incomplete substitution (3)

(iii) Name a device that uses a transformer. (6) mobile phone charger, television, power supply, washing machine, etc. any one (6) partial answer (3)

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