form 5 chapter 4 physics

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4. ELECTRONICS [/25 x 100 = % ]SECTION A Structured ItemsInstruction:Answerall questions in this section.

4.1 Understanding the uses of the Cathode Ray Oscilloscope (C.R.O)

A student is able to :

explain thermionic emission. Describe the properties of cathode rays. Describe the uses of a cathode ray oscilloscope.

-- Measure potential difference using the C.R.O.-- Measure short time intervals using the C.R.O.-- Display wave forms using the C.R.O.

Solve problems based on the C.R.O. display

1. ______________________is the process where by____________are released from thesurface of a heated metal.

2. The properties of cathode rays

(i) They travel in________________lines.(ii) They are fast moving____________and therefore can generate________when

they hit the fluorescent screen.(iii) They are deflected by_________and____________fields and are_________

charged.

3. The diagram shows the structure of a simple cathode ray tube.

(b) The CRO can be used to :

(a) Name the components labeled P, Q, R, S and T.

Component Name of the component Function of the componentPQRST

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i. display _________________ii. measure________________of DC and AC supplyiii. measure a_________________________

4. The figure below shows a trace formed on the screen of a CRO.

If the Y-gain control on the CRO is set at 0.5 V cm-1 and the time-base is set at 5 mscm-1.

Find the peak voltage VP , Period, T and Frequency, f.

peak voltage VP Period, T Frequency, f.

Peak voltage, VP==

Period, T ==

frequency, f = 1/T==

5. If the same signal is applied to the CRO but the time base is readjusted to 10 ms/cm,draw a sketch to show the trace that will now be formed on the screen?

4.2 Understanding semiconductor diodes. [ ../31 x 100 = % ]

1. (a) A semiconductor is a material whose resistance is between the resistance of a_______________ and an ____________________.

(b) ___________ is a process when small amounts of ________________ are added topure semiconductors causing an increase in the _________________ of the material.

(c) A p-type semiconductor is produced when a semiconductor material such_________________ is doped with a ____________ element like _________________

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(d) A n-type semiconductor is produced when a semiconductor material such asgermanium/silicon is doped with a ____________________ element like_____________________.

. (e) A ______________________ is a p-n junction diode where the p-type material iscalled the __________ and the n-type material is called the ______________

(g) _____________-biased,Bulb lights / does not light up

_______ _______Symbol of diode

(f) In ___________-biased a current ________ through the diode but in _________-biasedcurrent ________________ through the diode.

2. Diagram 1 shows an electric circuit with one diode and the trace produced is shown on aCRO connected across the resistor R.Diagram 2 shows an electric circuit with four diodes and the trace produced is shown on aCRO connected across the resistor R.

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(a) ________________ is a process to convert an alternating current into a_______________________ by using a _____________.

(b) Comparision between :Diagram 1 Diagram 2

The diode is connected in _________ tothe resistor R.

The diodes are connected in a____________ with two junctionsconnected to the power supply and theother two junction across the resistor R.

Diode is used as a ____________rectifier

Diode are used as a __________rectifier.

Both input are ______________ voltages and the outputs are _______________.

(c) Trace the path taken by the current in Diagram.2 if the terminal X is positive.

Current flows from _ _ _ _ _ _ _ _

(d) A _______________ is an electric component that needs to be connected to theoutput of both the circuits to produce a more constant output.

4.3 Understanding transistors [ ../18 x 100 = .. % ]

A student is able to: Describe a transistor in terms of its terminals. Describe how a transistor can be used as a current amplifier.

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X

Z

Y

Describe how a transistor can be used as an automatic switch.

1. Name the two types of transistors as shown in Figure 4.31(a) and 4.31(b) and labelthe three terminals

___________

_______

__________

Figure 4.31 (a) Type of transistor : _______ transistor

Figure 4.31 (b) Type of transistor : ________ transistor

2. Transistor as a Current Amplfier

A transistor can function as a______________________by allowing a small

current to control a larger current. Rheostat R changes the_______ current. A

_________change in the base current, IB will cause a _______ change in the

collector current, IC. The current amplification can be calculated as follows:

3. The diagram below shows a circuit which acts as an automatic switch to turn on the motor Mwhen the surroundings is dark.

5

X

Y

IC

IE

R1

R2

R IB

mA

A

Current AmplificationB

C

I

I

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(a) Name the component labeled P,Q and S.

Component Name of the componentsPQS

(b) What is the function of the component labeled R?

To control the ________current.

(c) The figure below shows how the collector current, Ic and the base current, Ib flow.

(d) What happens to the magnitude of the potential difference VS when the surroundingsbecome bright?Tick ( ) the correct answer in the box provided

IncreaseDecrease

(e) Explain how the change in the potential difference, VS, will cause the motor M to beturned on?

As VS ____________, the base current______________causing the collector currentto_______________by a large magnitude. This will cause the relay to___________the circuit and switch on the motor.

4.4 Analysing logic gates [ / 21 x 100 = % ]

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A student is able to: Draw symbols for the following logic gates .

i. ANDii. ORiii. N0Tiv. NAND

v. NOR Build truth tables for logic gates in combination for a maximum of 2 inputs. State that logic gates are switching circuits in computers and other electronic systems. Describe applications of logic gates control systems.

1. Draw symbols for the following logic gates and state their action in a truth table

i. AND ii. OR

iii. N0T iv. NAND

v. NOR

2. The figure below shows a circuit consisting of three different logic gates.

(a) Name the logic gates

Logic gate Name of the logic gatePQ

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S

(b) Complete the truth table for the system shown above.

Input OutputA B

0 00 1

1 0

1 1

(c) (i) The combination of the logic gates above can be replaced by a single logic gate.What is this equivalent logic gate?

(ii) Give the Boolean equation for the logic gate in your answer in ( c)(i) above.

2. The circuit below shows a logic circuit used in a cold room where frozen meat is stored. The

alarm will be turned on if the temperature of the cold room is too high. The buzzer will beturned OFF if the output logic is 0 and be turned ON if the output logic is 1.

(a) Name the logic gate used in the circuit above.

(b) Based on the information above, complete the truth table for the logic gate above.

Input Output Alarm1 00 1

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(c) Name the component labeled E.

(d) If the temperature of the cold room increases, what happens to the quantity in the table

below? Complete the table with the appropriate answers.

Resistance of ECurrent flowing through the logic gateCondition of the alarm

9.2.3 Transistor as an Automatic Switch.1. Complete the statement below.

The switching action is produced by using a potential divider. In aworking circuit shown in figure, a resistor, RX and a. are being used to form a potential divider. If thevariable resistor is set to zero, the base voltage is . And thetransistor switches . However, if the resistance of the

variable resistor is increased, the base voltage will. Whenthe base voltage reached a certain minimum value, the base

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current, IB switches on the transistor. A large collector current, ICflows to light up the bulb.

2. What type of transistor is used in an automatic switch circuit?

3. (a) Light Controlled Switch(i) Complete the statement below.

Figure shows a transistor-based circuit that functions as a lightcontrolled switch. The .. (LDR) has a very highresistance in the . and a low resistor in ... R is afixed . The LDR and R form a potential divider in thecircuit.In bright light, the LDR has a very . resistance compared to R.Therefore, the base voltage of the transistor is too .. to switchon the transistor.In darkness, the resistance of the LDR is very and thevoltage across the LDR is enough to switch on the transistor

and thus lights up the bulb. This circuit can be used toautomatically switch the bulb at night.

(ii) Complete the table below.

(iii) How can the circuit in figure be modified to switch on the lightat daytime?..

(b) A Heat-Controlled Switch

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(i) Complete the statement below.

Figure shows a transistor-based circuit that function as a heatcontrolled switch.A ..is a special type of resistor. Its resistance becomesvery when it is cold. When the thermistor is heated, itsresistance rapidly. At room temperature, the thermistorhas a . resistance compared to R. Therefore, the base voltageof the transistor is too low to switch on the transistor.When the thermistor is heated, its . drops considerablelycompared to R. Therefore, the ., VB is high enough toswitch . the transistor. When the transistor is switch on, therelay switch is activated and the relay is switched . Thecircuit can also be used in a fire alarm system.

(ii) What is the function of a diode is used in the heat-controlledcircuit?..

..(iii) Complete the table below.

9.2 . 4 Transistor as a Current Amplfier1. Complete the statement below.

A transistor functions as a current amplifier by allowing a smallcurrent to control a larger current. The magnitude of the

., IC is primarily determined by the .., IB. A.. change in the base current, IB will cause a .. change inthe collector current, IC. The current amplification can becalculated as follows:

2. Name the type of the transistor used.3. What will happened to the readings of the miliammeter, mA and

microammeter, A whenthe resistance of R is reduced?

4. A transistor is said to have two states, the ON state and OFFstate.

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(a) Explain the meaning of the ON state of a transistor.(b) Explain the meaning of the OFF state of a transistor.(c) What is the function of the rheostat, R?(d) What is the function of the resistor, S?

Reinforcement Chapter 9

Part A: Objective questions

1. Which of the following isnot a propertyof cathode rays?

A. It is positively charged.B. It travels in a straight line.C. It can be deflected bymagnetic field.D. It can be deflected byelectric field.

2. Cathode rays consists ofA. Fluorescent particlesB. Light rays from a screenC. Beams of fast moving

particlesD. Light rays from hot filament

3. A beam of electrons is beingdeflected due to a potentialdifference between plates Pand Q.Which of the followingstatements is nottrue?A. The potential at plate P ispositive.B. The deflection would begreater ifthe potential difference isgreater.C. The deflection would begreater ifthe electrons are movingfaster.D. The electron beam will

return tostraight line if a suitablemagnetic

field is applied between theplates.

4. The figure 9.34 shows thetracedisplayed on a CRO with the Y-gaincontrol is turned to 3.75 V/div.What is the maximum value ofthepotential difference being

measured?A. 2.5 VB. 5.5 VC. 7.5 VD. 12.5 VE. 15.0 V

5. In p-type semiconductorA. The number of holes areequal to the number ofelectrons.B. The number of the holes aremorethan the number of electrons.C. The number of the holes areless than the number ofelectrons.

6. Which of the following isnot true about diode?A. It can be used to rectify

alternatingcurrent.B. It can only conductelectricity when

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it is connected in forward inforwardbias in a circuit.C. It is formed by joining an n-type anda p-type semiconductor.D. The majority chargecarriers in thediode are electrons.

7. The figure 9. 35 shows thearrangement of silicon atomsafter an atom P is doped toform an extrinsicsemiconductor.

Which of the following is nottrue?A. The conductivity of thesemiconductor increases.B. The semiconductor becomesan ntype.

C. The majority charge carrieriselectron.D. Atom P is a trivalent atom.

8. The figure 9.36 shows arectifier circuit. Which of thefollowing statements is true?

A. A rectifier changes d.c toa.c.B. Device P allows current toflow inany directions.C. Device Q acts as a rectifier.D. The rectifier circuit would

still work if device P isreversed.

9. The figure 9.37 shows acircuitconsisting of two diodes and abulb.When the switch is on, thebulb does not light up. Whatneeds to be done to light upthe bulb?

A. Replace the diode with anew one.B. Reverse the connection ofthe diode.C. Increase the number of

bulbs.D. Connect a resistor in serieswith thebulb.

10. Figure 9.38 shows fouridentical bulbs, P, Q, R and S,and four electroniccomponents connected in acircuit.Which of the following bulbs

will lightup continuously when theswitch is on?

A. P and Q only

B. P, Q and R onlyC. R and S onlyD. P, Q and S only

11. Which of the followingcircuits shows the connectdirections of the base currentIB, emitter current, IE andcollector current, IC?

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12. Which of the followingstatements about a transistoris not true?A. A transistor can act as anamplifierB. A transistor can act as arelay switch.C. The function of a transistoris thesame as that of two diodes.

D. A transistor is acombination of twotypes of semiconductors.

13. What is the function of thetransistor circuit shown infigure 9.39?A. As an amplifierB. As a rectifierC. As a switch deviceD. As a modulator

14. The figure 9.40 shows atransistor being used as acurrent amplifier.Which of the following iscorrect?A. IB > ICB. IB = ICC. IB < IC

15. Figure 9.41 shows a circuit

consisting of a transistorwhich acts as an automaticswitch. When the potentialdifference across thethermistor is 3 V and theresistance of the thermistor is

1000 , the resistance valueof resistor, R is ..

A. 3 kB. 4 kC. 5 kD. 6 kE. 7 k

16. The figure 9. 42 shows atransistorcircuit being used to amplifysound.Which of the following is notcorrect

about the circuit?

A. T is an npn transistorB. The capasitor prevents d.ccurrent

but allows a.c current to passthroughit.C. Speaker amplifies thesound.D. R1 and R2 act as potentialdivider.

Part B: Structured Questions.

1. Figure 9.46 shows a traceobtained on an oscilloscopescreen when an a.c voltage isconnected to the Y-plates ofan oscilloscope.

(a) Explain what is meant bythermionic emission.(b) Determine the peakvoltage of a.c voltage.

(c) Determine the time for onecomplete oscillation on thescreen.

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(d) What is the frequency ofthe a.c voltage?

(e) With the same a.c voltageapplied to the oscilloscope,the time-base setting isaltered to 2.5 ms/cm and the

Y-gain setting is altered to 2V/cm. On the space below,sketch the new trace wouldappear on the oscilloscope.

2. Figure 9. 47 shows a fullwave bridge rectifier. The a.csupply has a frequency of 50Hz.

(a) When the polarity of the

a.c supply voltage is positiveat A, state the two diodeswhich are forward biased...(b) When the polarity of thea.c supply voltage is negativeat A, state the two diodeswhich are forward biased.

(c) Using the axes in figure9.48, sketch the voltage-timegraph across the resistor, R.

(d) On the figure 9.49, sketchthe voltage-time graph acrossthe resistor if a capacitor isconnected across the resistorif a capacitor is connectedacross the resistor R parallelwith the resistor.

(e) Explain how the capacitorcauses the voltage across theresistor to vary with time in

theway that you have drawn.

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form 5 chapter 4 physics

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