Electronics

TUTORIAL CHAPTER 4 : ELECTRONICS

Part A: Objective questions

1. Which of the following is not a property of cathode rays?A. It is positively charged.B. It travels in a straight line.C. It can be deflected by magnetic field.D. It can be deflected by electric 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 being deflected due to a potential difference between plates P and Q.

Which of the following statements is not true?A. The potential at plate P is positive.B. The deflection would be greater if

the potential difference is greater.C. The deflection would be greater if

the electrons are moving faster.D. The electron beam will return to

straight line if a suitable magnetic field is applied between the plates.

4. The figure 9.34 shows the trace displayed on a CRO with the Y-gain control is turned to 3.75 V/div.What is the maximum value of the potential 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 are equal to the

number of electrons.B. The number of the holes are more

than the number of electrons.C. The number of the holes are less than

the number of electrons.

6. Which of the following is not true about diode?A. It can be used to rectify alternating

current.B. It can only conduct electricity when

it is connected in forward in forward bias in a circuit.

C. It is formed by joining an n-type and a p-type semiconductor.

D. The majority charge carriers in the diode are electrons.

7. The figure 9. 35 shows the arrangement of silicon atoms after an atom P is doped to form an extrinsic semiconductor.

Which of the following is not true?A. The conductivity of the

semiconductor increases.B. The semiconductor becomes an n-

type.C. The majority charge carrier is

electron.D. Atom P is a trivalent atom.

Strive to A+ 1 Physics Unit 2011

Figure 9.34

P

Q

Figure 9.33

Figure 9.35


8. The figure 9.36 shows a rectifier circuit.Which of the following statements is true?

A. A rectifier changes d.c to a.c.B. Device P allows current to flow in

any directions.C. Device Q acts as a rectifier.D. The rectifier circuit would still work

if device P is reversed.

9. Which of the following statements about a transistor is not true?A. A transistor can act as an amplifierB. A transistor can act as a relay switch.C. The function of a transistor is the

same as that of two diodes.D. A transistor is a combination of two

types of semiconductors.

10. What is the function of the transistor circuit shown in figure 9.39?A. As an amplifierB. As a rectifierC. As a switch deviceD. As a modulator

11. The figure 9.40 shows a transistor being used as a current amplifier.

Which of the following is correct?A. IB > IC

B. IB = IC

C. IB < IC

12. The figure 9. 42 shows a transistor circuit being used to amplify sound.

Which of the following is not correct about the circuit?A. T is an npn transistorB. The capasitor prevents d.c current

but allows a.c current to pass through it.

C. Speaker amplifies the sound.D. R1 and R2 act as potential divider.

13. The figure 9.43 shows a logic gate circuit with input signals, X and Y.

Which of the following is the output signal?


Figure 9.36

IBIC

Figure 9.40

M- MicrophoneC- CapacitorS- Speaker

Figure 9.42

Figure 9.43

P

Q

Figure 9.39


14. The figure 9.44 shows a logic gate circuit.

Which of the following is the output signal Z?A. 0110B. 1010C. 1110D. 0101

15. The figure 9.44 shows the combination of three logic gates.

The truth table for the combination of tree logic gates is as follows.What is gate X?A. ANDB. NORC. ORD. NAND

16. The figure 9. 45 shows a combination of three logic gates in a logic circuit. When inputs P and Q are both 1 output Y is 1.

Which of the following logic gates can be used to represent J and K?

A.B.C.D.

J KAND NOR

NAND NOROR AND

NOR AND


Figure 9.43

Figure 9.44

YJ

K

Figure 9.45


Part B: Structured Questions1. Figure 9.46 shows a trace obtained on an oscilloscope screen when an a.c voltage is

connected to the Y-plates of an oscilloscope.

(a) Explain what is meant by thermionic emission.

………………………………………………………………………………………………(b) Determine the peak voltage of a.c voltage.

………………………………………………………………………………………………(c) Determine the time for one complete oscillation on the screen.

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

………………………………………………………………………………………………(e) With the same a.c voltage applied to the oscilloscope, the time-base setting is altered to

2.5 ms/cm and the Y-gain setting is altered to 2 V/cm. On the space below, sketch the new trace would appear on the oscilloscope.

2. Figure 9. 47 shows a full wave bridge rectifier. The a.c supply has a frequency of 50 Hz.

(a) When the polarity of the a.c supply voltage is positive at A, state the two diodes which are forward biased.…………………………………………………………………………………………..

Figure 9.46

Emission of electrons from the surface of a metal by heat.

2 x 3 = 6V

2 x 5 = 10 ms

f =1/T=50 Hz

D1 and D3

Figure 9.47

Scale: 1 division = 1 cmThe Y-gain is set at 3 V/cmThe time base is set at 5 ms/cm



(b) When the polarity of the a.c supply voltage is negative at A, state the two diodes which are forward biased.……………………………………………………………………………………………

(c) Using the axes in figure 9.48, sketch the voltage-time graph across the resistor, R.

(d) On the figure 9.49, sketch the voltage-time graph across the resistor if a capacitor is connected across the resistor if a capacitor is connected across the resistor R parallel with the resistor.

(e) Explain how the capacitor causes the voltage across the resistor to vary with time in the way that you have drawn.………………………………………………………………………………………………………………………………………………………………………………………………

3. A student wants to build a simple lift motor control system which operates using two buttons, A and B for a two-storey building.A: Up buttonB: Down buttonThe lift motor only activates when someone presses any one of the buttons. Figure 9.50 shows the circuit that can be used to activate the motor.

Keys: Buttons A and B : When pressed, logic “1”

Not pressed, logic ”0”X Output : Motor is activated, logic “1”

Time/ms

Voltage/V

Figure 9.48

Time/ms

Voltage/V

Figure 9.49

12 V

0 V

A

B

Logic gate

X 240 V

Relay switch Motor

Figure 9.50



(a) The truth table below shows the operations of the logic gates in a lift motor control system.

(i) Using the keys given, complete the truth table.

(ii) Name the logic gate in the circuit in the

figure 9.50.…………………………………………………………………………………

(iii) In the space below, draw the logic gate symbol in 3(a)(ii).

Why is a relay switch needed in the circuit?………………………………………………………………………………………………

(b) The door of the lift is fitted with a light transmitter and a detector which is a light dependent resistor, LDR. If the light dependent resistor detects light, the relay switch is activated and the lift door will close. Figure 9.51 shows an electronic circuit for the control system of the lift door.

(i) State the relationship between the resistance and the intensity of light received by the light dependent resistor, LDR.…………………………………………………………………………………

(ii) Complete the circuit in figure 9.51 by drawing the resistor and the light dependent resistor using the symbols given below.

(iii) Explain how the circuit functions. ……………………………………………………………………………………………………………………………………………………………………

Part C: Essay Questions1.

Input OutputA B X0 0 00 1 11 0 11 1 0

RMotor

240 V

Resistor Light dependent resistor

Figure 9.51



(a) The diode, bulb and battery in circuit X and circuit Y of figures 9.52 and 9.53 are identical.

(i) What is meant by a direct current and an alternating current? [2 marks](ii) Using Figures 9.52 and figure 9.53, compare the connection of the diodes and the conditions

of the bulbs. Relating the connection of the diodes and the conditions of the bulbs, deduce the function of a diode. [5 marks]

(iii) State the use of a diode. [1 mark](b) A semiconductor diode is made by joining a p-type semiconductor with a n-type semiconductor.

Describe and explain the production and the characteristics of a p-type semiconductor and a n-type semiconductor. [4 marks]

2. Figure 9.55 shows four circuits W, X, Y and Z, each has an ideal transformer and the circuit are used for the purpose of rectification.

(i) What is meant by rectification? [1mark](ii) Explain the working principle of a transformer. [3 marks](iii) You are asked to make a 12 V battery charger. Study the circuits W, X, Y and Z in figures

9.55 and consider the following aspects:Type of transformerThe number of turns in the primary coil and in the secondary coil.Type of rectificationCharacteristics of output current

Explain the suitability of the above aspects and hence, determine the most suitable circuit to make the battery charge. [6 marks]

Figure 9.52 Figure 9.53

Circuit W

Circuit X

Circuit Y

Circuit Z



3. Figure 9.58 shows a microphone connected to a power amplifier. When the microphone

has detected a sound, an amplified sound is given out through the loudspeaker. The sound

becomes louder if the volume of the amplifier is turned on to increase the power.

Using the information based on the observation of the brightness of the bulbs,

(a) Make one suitable inference.

(b) State one appropriate hypothesis that could be investigated.

(c) Design an experiment to investigate the hypothesis stated in (b). Choose suitable

apparatus such as a diode, rheostat and others.

In your description, state clearly the following:

(i) Aim of the experiment,

(ii) Variables in the experiment,

(iii) List of apparatus and materials,

(iv) Arrangement of the apparatus,

(v) The procedure of the experiment, which includes the method of controlling the

manipulated variable and the method of measuring the responding variable,

(vi) The way you would tabulate the data,

(vii) That way you would analyse the data.

Figure 9.58

LoudspeakerPower amplifier

Volume control

Microphone


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