experiments in l.c. physics

BY A G E N T L E M A N

EXPERIMENTS IN L.C. PHYSICS

MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR

• Given the formula

vuf

111

MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR

u

v

Lamp-box

Crosswire

Screen

Concave mirror

Approximate focal length by focusing image of window onto sheet of paper. (Mirror to sheet is approx. f measure with a meter stick)

Place the lamp-box well outside the approximate focal length (Avoid a virtual image)

Move the screen until a clear sharp inverted image of the crosswire is obtained.

Measure the distance u from the crosswire to the mirror, using the metre stick.

Measure the distance v from the screen to the mirror. Repeat this procedure for different values of u. Calculate f each time and then find an average value.

Precautions The largest errors are in parralax when

measuring with the meter rule and finding the exact position of the sharpest image.

VERIFICATION OF SNELL’S LAW OF REFRACTION

Glass Block

Trace the ray of light to find i and r

VERIFICATION OF SNELL’S LAW OF REFRACTION

i

r

Lamp-box 0 - 360° Protractor

Glass Block

1. Place a glass block on the 0-3600 protractor in the position shown on the diagram and mark its outline.

2. Shine a ray of light from a lamp-box at a specified angle to the near side of the block and note the angle of incidence.

3. Mark the exact point B where it leaves the glass block.

4. Remove the glass block. Join marks to trace ray.

• Measure the angle of refraction r with protractor.

• Repeat for different values of i.• Draw up a table and Plot a graph of sin i

against sin r.• The slope is refractive index, n• Do not use small i as then r too small to

measure accurately

sin r.

sin i

Cork

Pin

MirrorApparent depth

Pin

Image

Water

Real depth

MEASUREMENT OF THE REFRACTIVE INDEX OF A LIQUID

FINDING NO PARALLAX – LOOKING DOWN

Pin atbottom

Pin reflectionin mirror

Parallax No Parallax

Set up the apparatus as shown.

Adjust the height of the pin in the cork above the mirror until there is no parallax between its image in the mirror and the image of the pin in the water.

Measure the distance from the pin in the cork to the back of the mirror – this is the apparent depth.

Measure the depth of the container – this is the real depth. Use a metre stick.

Calculate the refractive index n= Real/Apparent

Repeat using different size containers and get an average value for n.

u v

Lamp-box with crosswire Lens Screen

MEASUREMENT OF THE FOCAL LENGTH OF A CONVERGING LENS

1. Place the lamp-box well outside the approximate focal length (Use window focus method again/meter stick)2. Move the screen until a sharp inverted image of the crosswire is obtained. 3. Measure the distance u from the crosswire to the lens, using the metre stick.4. Measure the distance v from the screen to the lens using the metre stick.5. Calculate the focal length of the lens using

6. Repeat this procedure for different values of u. 7.Calculate f each time and then find the average

value. Avoid parralax

vuf

111

MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A

MECHANICAL METHOD

Cotton wool

Water

Copper rivets

Boiling tube

Heat source

MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A

MECHANICAL METHOD

10°C

CalorimeterLagging

Cotton wool

Water

Copper rivets

Boiling tube

Heat source

Digitalthermometer

Water

1. Place some copper rivets in a boiling tube. Fill a beaker with water and place the boiling tube in it.2. Heat the beaker until the water boils. Allow boiling for a further five minutes to ensure that the copper pieces are 100° C.3. Find the mass of the copper calorimeter mcal.4. Fill the calorimeter, one quarter full with cold water. Find the combined mass of the calorimeter and water m1.5. Record the initial temperature of the calorimeter plus water θ1. Place in lagging6. Quickly add the hot copper rivets to the calorimeter, without splashing.7. Stir the water and record the highest temperature θ2.8. Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mco.

6. Quickly add the hot copper rivets to the calorimeter, without splashing.7. Stir the water and record the highest temperature θ2.8. Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mco.

Heat lost by the Riverts=Heat gained by water and calorimeter

mco cco = mw cw + mc cc

MEASUREMENT OF THE SPECIFIC LATENT HEAT OF FUSION OF ICE

How do we measure it…….• Pretty much• Problems

1. Ice not all at same temperature2. Covered in water

3. Heat loss/Gain to surroundings

MEASUREMENT OF THE SPECIFIC LATENT HEAT OF FUSION OF ICE

Wrap ice in cloth to crush and dry.

Calorimeter

Lagging

Crushed ice

Water

Digitalthermometer

10°C

1. Place some ice cubes in a beaker of water and keep until the ice-water mixture reaches 0 °C.2. Find the mass of the calorimeter mcal. Surround with lagging3. Half fill the calorimeter with water warmed to approximately 10 °C above room temperature. Find the combined mass of the calorimeter and water m2. 4. Record the initial temperature θ1 of the calorimeter plus water.5. Surround the ice cubes with kitchen paper or a cloth and crush them between wooden blocks – dry them with the kitchen paper. 6. Add the pieces of dry crushed ice, a little at a time, to the calorimeter. 7. Record the lowest temperature θ2 of the calorimeter.Find the mass of the calorimeter + water + melted ice m3

CALCULATIONS

ENERGY GAINED BY ICE = ENERGY LOST BY CALORIMETER + ENERGY LOST BY THE WATER.

MIL +MICW 1= MCALCC 2+MWCW 2

MEASUREMENT OF THE SPECIFIC LATENT HEAT OF VAPORISATION OF WATER

Heat source

10°C

Lagging

DigitalThermometer

Water

Steam Trap

Calorimeter

1. Set up as shown2. Find the mass of the calorimeter mcal.3. Half fill the calorimeter with water cooled to approximately 10 °C below room temperature.4. Find the mass m1 of the water plus calorimeter.5. Record the temperature of the calorimeter + water θ1.

6. Allow dry steam to pass into the water in the calorimeter until temperature has risen by about 20 °C.7. Remove the steam delivery tube from the water, taking care not to remove any water from the calorimeter in the process.8. Record the final temperature θ2 of the calorimeter plus water plus condensed steam. 9. Find the mass of the calorimeter plus water plus condensed steam m2.

ENERGY LOST BY STEAM = ENERGY GAINED BY CALORIMETER + ENERGY GAINED BY THE WATER

MSL+MSCW ∆ = MCALCC ∆ +MWCW.∆

Split cork

lBob

20:30

Timer

INVESTIGATION OF THE RELATIONSHIP BETWEEN PERIOD AND LENGTH FOR A

SIMPLE PENDULUM AND HENCE CALCULATION OF g

1. PLACE THE THREAD OF THE PENDULUM BETWEEN TWO HALVES OF A CORK AND CLAMP TO A STAND.2. SET THE LENGTH OF THE THREAD AT ONE METRE FROM THE BOTTOM OF THE CORK TO THE CENTRE OF THE BOB. 3. SET THE PENDULUM SWINGING THROUGH A SMALL ANGLE (<10°). MEASURE THE TIME T FOR THIRTY COMPLETE OSCILLATIONS.4. DIVIDE THIS TIME T BY THIRTY TO GET THE PERIODIC TIME T.5. REPEAT FOR DIFFERENT LENGTHS OF THE PENDULUM. (ALT MEASURE STRING WITH METRE STICK AND BOB WITH VERNIER CALIPERS AND DIVIDE BY 2 AND ADD)

(slope)

4 g

slope 4

4

2

22

22

gl

Tg

lT

l

T2

n = 2

n = 1

n = 2

n = 1

n = 0

x

D

Laser

Metre stick

Diffractiongrating

θ

Tan θ = x/D

MEASUREMENT OF THE WAVELENGTH OF MONOCHROMATIC LIGHT

1. Set up the apparatus as shown. Observe the interference pattern on the metre stick – a series of bright spots.2. Calculate the mean distance x between the centre (n=1) bright spot and the first (n =1) bright spot on both sides of centre.3. Measure the distance D from the grating to the metre stick.4. Calculate θ on both sides and find average5. Calculate the distance d between the slits, using d=1/N the grating number. (e.g. N=300 lines/mm)Calculate the wavelength λ using nλ = dsinθ. 6. Repeat this procedure for different values of n and get the average value for λ

RESISTIVITY OF THE MATERIAL OF A WIRE

Micrometer

Metre stick

l

Bench clamp

Stand

Nichrome wire Crocodile clips

METHOD

1. Note the resistance of the leads when the crocodile clips are connected together. Could also be precaution.

2. Stretch the wire enough to remove any kinks or ‘slack’ in the wire.

3.Read the resistance of the leads plus the resistance of wire between the crocodile clips from the ohmmeter. Subtract the resistance of the leads to get R.

4.Measure the length l of the wire between the crocodile clips, with the metre stick.

5.Increase the distance between the crocodile clips. Measure the new values of R and l and tabulate the results.

6.Make a note of the zero error on the micrometre. Find the average value of the diameter d.

1. Calculate the resistivity where A =

2. Calculate the average value for .

Precautions Ensure wire is straight and has no kinks like ....Take the diameter of the wire at different angles

,Al

Rρ

4

2d

INVESTIGATION OF THE LAWS OF EQUILIBRIUM FOR A SET OF CO-PLANAR FORCES

Newton balance

Newton balance

Support

w1w2 w3

1. Use balancing the metre stick on a fulcrum to find the centre of gravity and a digital scale to find the mass of the metre stick and its weight.

2. The apparatus was set up as shown and a equilibrium point found when system not moving. (Metre stick horizontal)

3. Record the reading on each Newton balance.

4. Record the positions on the metre stick of each weight, each Newton balance and the centre of gravity of the metre stick

FOR EACH SITUATION (1) FORCES UP = FORCES DOWNI.E. THE SUM OF THE READINGS ON THE BALANCES SHOULD BE EQUAL TO THE SUM OF THE WEIGHTS PLUS THE WEIGHT OF THE METRE STICK.

(2)The sum of the clockwise moments about an axis through any of the chosen points should be equal to the sum of the anticlockwise moments about the same axis.

MEASUREMENT OF THE SPEED OF SOUND IN AIR

Tuning fork

Tube

Water

l1 Graduated cylinder

d

λ = 4(l1 + 0.3d)

1. Strike the highest frequency (512 Hz) tuning fork and hold it in a horizontal position just above the mouth of the tube.

2. Slide the tube slowly up from zero (To get fundamental frequency) until the note heard from the tube is at its loudest; resonance is now occurring.

3. Measure the length of the air column (from the water level to the top of the tube) l1 with a metre stick.

Method

• An end correction factor has to be added to the length e = 0.3d, where d is the average internal diameter of the tube (measured using a vernier callipers).• Hence λ = 4(l1 + 0.3d) • c = f• c = 4f(l1 + 0.3d). • Calculate a value of c for each tuning fork

and find an average value for the speed of sound.

Method

TO SHOW THAT a µ F

Card

l

t1t2

s

Dual timer

Light beam

Photogate

Pulley

Air track

Slotted weights

TO SHOW THAT a µ F

t1

Dual timer

Light beam

Photogate

t1 time for card to pass first photo-gate

TO SHOW THAT a µ F

t1

Dual timer

Light beam

Photogate

t2 time for card to pass second photo-gate

t2

PROCEDURE

Set up the apparatus as in the diagram. Make sure the card cuts both light beams as it passes along the track.

Level the air track. (Set one car and adjust so little drift when released)

Set the weight F at 1 N (10 x 0.1N). Release the vehicle.

Note the times t1 and t2. Remove one 0.1 N disc from the slotted weight,

store this on the vehicle, and repeat. Continue for values of F from 1.0 N to 0.1 N. Use a metre-stick to measure the length of the card

l and the separation of the photo gate beams s.

Remember to include the following table to get full marks. All tables are worth 3 marks when the Data has to be changed. Draw a graph of a/m s-2 against F/N Straight line though origin proves Newton's second law

1t

lu

2t

lv

s

uva

2

22

F/N t1/s t2/s V/m/s U/m.s A/m/s2

VERIFICATION OF THE PRINCIPLE OF CONSERVATION OF MOMENTUM

Velcro pad

Dual timer Photogate

Air track

t1t2

Light beamCardl

Vehicle 1 Vehicle 2

1.Set up apparatus as in the diagram.2. Level the air-track. To see if the track is level carry

out these tests:(A vehicle placed on a level track should not drift

toward either end)3. Measure the mass of each vehicle m1 and m2

respectively, including attachments, using a balance.

4. Measure the length l of the black card in metres.5. With vehicle 2 stationary, give vehicle 1 a gentle

push. After collision the two vehicles coalesce and move off together.

6 Read the transit times t1and t2 for the card through the two beams.

CALCULATE THE VELOCITY BEFORE THE COLLISION, AND AFTER THE COLLISION,

MOMENTUM BEFORE THE COLLISION = M1U MOMENTUM AFTER THE COLLISION = (M1 + M2) V.

SHOULD BE THE SAME (UNITS ARE KG M/S)

REPEAT SEVERAL TIMES, WITH DIFFERENT VELOCITIES AND DIFFERENT MASSES.

1t

lu

2t

lv

Questions

• Forces to be counteredFriction – by cushion of airGravity – level air track with a spirit level

MeasurementsMass, length of card and time to pass gate

CalculationsVelocity= Distance/time

MEASUREMENT OF g

h

SwitchElectromagnet

Ball bearing

Trapdoor

Electronic timer

When the switch opens the ball falls

The timer records the time from when the switch opens until trap door opens

Set up the apparatus. The millisecond timer starts when the ball is released and stops when the ball hits the trapdoor

Measure the height h as shown, using a metre stick.

Release the ball and record the time t from the millisecond timer.

Repeat three times for this height h and take the smallest time as the correct value for t.

Repeat for different values of h.

Calculate the values for g using the equation . Obtain an average value for g.

Place a piece of paper between the ball bearing and the electromagnet to ensure a quick release

221 gth

VERIFICATION OF BOYLE’S LAW

Bicycle pump

Reservoir of oil

Pressure gauge

Tube with volume of air trapped by oil

Volumescale

Valve

Using the pump, increase the pressure on the air in the tube. Close the valve and wait 20 s to allow the temperature of the enclosed air to reach equilibrium.

Read the volume V of the air column from the scale.

Take the corresponding pressure reading from the gauge and record the pressure P of the trapped air.

Reduce the pressure by opening the valve slightly – this causes an increase the volume of the trapped air column. Again let the temperature of the enclosed air reach equilibrium.

Record the corresponding values for the volume V and pressure P .

Repeat steps two to five to get at least six pairs of readings.

Plot a graph of P against 1/V. (Do not forget to draw up table) A straight-line graph through the origin will verify that, for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume, i.e. Boyle’s law.

P

1/V

CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A

STANDARD

Heat source

Mercury thermometer

Boiling tube

Glycerol Water

Thermistor

Multimeter as ohmmeter

1. Set up apparatus as shown in the diagram.2. Place the mercury thermometer and the

thermistor in the boiling tube.3. Record the temperature , in C, from the

mercury thermometer and the corresponding thermistor resistance R, in ohms, from the ohmmeter.

4. Increase the temperature of the glycerol by 5

C.5. Again record the temperature and the

corresponding thermistor resistance.6. Repeat the procedure until at least ten sets of

readings have been recorded.7. Plot a graph of resistance R against

temperature and join the points in a smooth, continuous curve.

MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL BY AN ELECTRICAL METHOD

Heating coil

LaggingMetal block

12 V a.c. Power supply

Joulemeter

350 J

10°C

Glycerol

1. Find the mass of the metal block m.2. Set up the apparatus as shown in the diagram.3. Record the initial temperature θ1 of the metal block.4. Plug in the joulemeter and switch it on.5. Zero the joulemeter and allow current to flow until there is a temperature rise of 10 C.6. Switch off the power supply, allow time for the heat energy to spread throughout the metal block and record the highest temperature θ2.7. The rise in temperature is therefore θ2 – θ1.8. Record the final joulemeter reading Q.

Energy supplied electrically = Energy gained by metal block

Q = mc.

MEASUREMENT OF SPECIFIC HEAT CAPACITY OF WATER BY AN ELECTRICAL METHOD

Calorimeter

Water

Heating coil

Lagging

350 J

Joulemeter12 V a.c. Power supply

Cover Digitalthermometer

10°C

1. Find the mass of the calorimeter mcal.2. Find the mass of the calorimeter plus the water m1. Hence the mass of the water mw is m1 – mcal.3. Set up the apparatus as shown. Record the initial temperature θ1.

4. Plug in the joulemeter , switch it on and zero it.5. Switch on the power supply and allow current to flow until a temperature rise of 10 C has been achieved.6. Switch off the power supply, stir the water well and record the highest temperature θ2. Hence the rise in temperature is θ2 – θ1. 7. Record the final joulemeter reading Q.

Precautions 1/. Lagging

2/. Cool water slightly so final temperature not far from room temperature.

Electrical energy supplied = energy gained by (water +calorimeter)

Q = mwcw + mcalccal.θ θ

JOULES LAW

Heating coil Lagging

Calorimeter Water

A

LidDigitalthermometer

10°C

METHOD

1. Put sufficient water in a calorimeter to cover the heating coil. Set up the circuit as shown.

2.Note the temperature. 3.Switch on the power and simultaneously start the

stopwatch. Allow a current of 0.5 A to flow for five minutes. Make sure the current stays constant throughout; adjust the rheostat if necessary.

4.Note the current, using the ammeter. 5.Note the time for which the current flowed. 6.Stir and note the highest temperature. Calculate

the change in temperature ∆.

CALCULATION AND GRAPH

Repeat the above procedure for increasing values of current I, taking care not to exceed the current rating marked on the rheostat or the power supply. Take at least six readings. Plot a graph of ∆(Y-axis) against I 2 (X-axis).

A straight-line graph through the origin verifies that ∆ I 2 i.e. Joule’s law.

Electrical Power lost as Heat P I2 is Joules lawThe power lost (Rate at which heat is produced) is

proportional to the square of the current.

∆

I2

VARIATION OF THE RESISTANCE OF A METALLIC CONDUCTOR WITH TEMPERATURE

Water Wire wound on frame

Glycerol

Heat source

10ºC

Digitalthermometer

Ω

10º C

1. Set up as shown.2. Use the thermometer to note the

temperature of the glycerol, which is also the temperature of the coil.

3. Record the resistance of the coil of wire using the ohmmeter.

4. Heat the beaker.5. For each 10 C rise in temperature record

the resistance and temperature using the ohmmeter and the thermometer.

6. Plot a graph of resistance against temperature.

Method

GRAPH AND PRECAUTIONS

Precautions - Heat the water slowly so temperature does

not rise at end of experiment-Wait until glycerol is the same temperature as

water before taking a reading.

R

THE VARIATION OF THE RESISTANCE OF A THERMISTOR WITH TEMPERATIURE

Thermistor

Digitalthermometer

10°C

Water

Heat source

Ω

Glycerol

METHOD

1. Set up the apparatus as shown.2. Use the thermometer to note the

temperature of the glycerol and thermistor.3. Record the resistance of the thermistor

using the ohmmeter.4. Heat the beaker.5. For each 10 C rise in temperature, record

the resistance and the temperature using the ohmmeter and the thermometer.

6. Plot a graph of resistance against temperature and join the points in a smooth, continuous curve.

PRECAUTIONS

• Heat the water slowly so temperature does not rise at end of experiment• Wait until glycerol is the same

temperature as water before taking a reading.

VARIATION OF CURRENT (I) WITH P.D. (V)

A

V+

6 V-

Nichrome wire

METHOD

1. Set up the circuit as shown and set the voltage supply at 6 V d.c.

2.Adjust the potential divider to obtain different values for the voltage V and hence for the current I.

3.Obtain at least six values for V and I using the voltmeter and the ammeter.

4.Plot a graph of V against I

VARIATIONS

(a) A METALLIC CONDUCTORWith a wire

(b) A FILAMENT BULB (c) COPPER SULFATE SOLUTION WITH

COPPER ELECTRODES(d) SEMICONDUCTOR DIODE

Done both ways with a milli-Ammeter and the a micro Ammeter


mA

V

+6 V

-

Diode in forward bias


+6 V

-

Diode in Reverse bias

V

A

INVESTIGATION OF THE VARIATION OF FUNDAMENTAL FREQUENCY OF A STRETCHED STRING WITH LENGTH

Bridge

l

Paper rider

Sonometer

Tuning Fork

Place the bridges as far apart as possible.Strike the turning fork putting the end on the bridge and reduce the length until the maximum vibration is reached (the light paper rider should jump off the wire).Measure the length with a metre rule.Note the value of this frequency on the tuning fork.Repeat this procedure for different tuning forks and measure the corresponding lengths.

PLOT A GRAPH OF FREQUENCY F AGAINST INVERSE OF LENGTH, .l

1

l

1

f

INVESTIGATION OF THE VARIATION OF THE FUNDAMENTAL FREQUENCY OF A STRETCHED

STRING WITH TENSION

Bridge

Paper rider

Sonometer

Pulley

Weight

Tuning Fork

• Select a wire length l (e.g. 30 cm), by suitable placement of the bridges. Keep this length fixed throughout the experiment.

• Strike the tuning fork and hold it on the bridge.

• Increase the tension by adding weight slowly from lowest possible until resonance occurs. (Jumping paper)

• Note tension from weight used (In Newtons) and frequency from the tuning fork.

• Repeat for different forks.

Method

PLOT A GRAPH OF FREQUENCY F AGAINST SQUARE ROOT OF THE TENSION

f

T

There you are and good luck

experiments in l.c. physics

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