# PHYSICS QUESTIONS AND ANSWERS (8)

1. A transistor function mainly as a

A.Â switch and amplifier

B.Â rectifier and an amplifier

C.Â charge storer and an amplifier

D.Â charge storer and a switch

2. A capacitor of 20 x 10-12F and an inductor are joined in series. The value of the inductance that will give the circuit a resonance frequency of 200kHz is

A.Â 1/16 H

B.Â 1/8 H

C.Â 1/64 H

D.Â 1/32 H

3. In the diagram above, determine the r.m.s current

A.Â 31A

B.Â 48A

C.Â 60A

D.Â 80A

4. Pure silicon can be converted to a p-type by adding a controlled amount of

A.Â trivalent atoms

B.Â tetravalent atoms

C.Â pentavalent atoms

D.Â hexavalent atoms

5. When an alternating current given by i = 10sin (120Ï€)t passes through a 12Î© resistor, the power dissipated in the resistor is

A.Â 1200W

B.Â 600W

C.Â 120W

D.Â 30W230

6. In a semi conductor junction diode, as the depletion or barrier layer is forward-biased, the layer

A.Â widens

B.Â narrows

C.Â remains constant

D.Â widens then narrows

7. In a tuned radio receiver R, L, C series circuit for resonance, the inductive and capacitive reactance XLÂ and XCÂ respectively are related as

A.Â XLÂ = XC

B.Â XLÂ =Â 1/2XC

C.Â XLÂ =Â 1/XC

D.Â XLÂ = 2XC

8. In an a.c circuit that contains only a capacitor, the voltage lags behind the current by

A.Â 180Â°

B.Â 90Â°

C.Â 60Â°

D.Â 30Â°

9. When impurities are added to semi-conductors, the conductivity of the semi-conductor

A.Â increases then decreases

B.Â increases

C.Â decreases

D.Â remains constant

10. A 120 V, 60 W lamp is to be operated on 220 V a.c. the supply mains. calculate the values of non-inductive resistance that would be required to ensure that the lamp is run on current value.

A.Â 100 â„¦ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B.Â 200 â„¦

C.Â 300 â„¦ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D.Â 500 â„¦

11. The bond that forms a semiconductor is?

A.Â covalent

B.Â electrovalent

C.Â ionic

D.Â metallic

12. Silicon doped with aluminum and germanium doped with arsenic become?

A.Â p- and n- types respectively

B.Â n- and p- type respectively

C.Â p- type semiconductors

D.Â n- type semiconductors

13. In Homes, electrical appliances and lamps are connected in parallel because

A.Â Parallel connections do not heat up the wires

B.Â series connections use high voltage

C.Â less current will be used

D.Â less voltage will be used1

00

14. In alternating current circuit at resonance, the angle of lead or lag is

A.Â Ï€ ​​ ​​ ​​​​ B.Â Ï€/2 ​​ ​​ ​​ ​​ ​​​​ C.Â Ï€/3 ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D.Â 0

15. The p-n junction diodes can act as rectifiers because they

A.Â conduct current when forward-biased

B.Â conduct current when reverse-biased

C.Â block current when forward-biased

D.Â conduct current in both directions

3

16. If a reverse-biased voltage is applied across a p-n junction, the depletion layer width is

A.Â increased

B.Â decreased

C.Â constant

D.Â halved

17. Determine the inductive reactance when a 30.0mH inductor with a negligible resistance is connected to a 1.3 x 103Hz oscillator.

A.Â 39.0Î© ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B.Â 122.5Î©

C.Â 245.0Î© ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D.Â 39000.0Î©

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17

18. High Tension (H.T.) transmission means

A.Â to transmit a given amount of power, the tension in the conducting wire must be high

B.Â heat is not lost when current is passed through a conductor

C.Â heat is gained when a given power is transmitted

D.Â a big transformer is required to transmit power

E.Â transmission of power at low current and high voltage

19.​​ I. Small size.
II. Low power requirement

III. Not easily damaged by high temperature

IV. Highly durable.​​

Which of the above are the advantages of semiconductors?

A.Â I, II and​​ III​​ only

B.Â II,​​ III​​ and​​ IV​​ only

C.Â I, II and​​ IV only

D.Â I,​​ II,​​ III​​ and IV

20. The r.m.s value of a supply voltage is quoted at 200V. What is the approximate peak value of the voltage?

A.Â 200volts ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B.Â 300volts

C.Â 283volts ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D.Â 250volts

1. A

2. D

3. B

4. A

5. B

6. B

7. A

8. B

9. B

11. B

12. A

13. A

14. D

15. A

16. A

17. C

18. E

19. D

20. C

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