HSSC-II (Class-12) Solved Physics MCQs; Unit-15: Alternating Current; (New Book/KPK Text Board, Peshawar) With Verified Answers

1. The r.m.s. value of a sine wave is 100 A. Its peak value is

A. 70.7 A
B. 141.4 A
C. 150 A
D. 282.8 A

... Answer is B. 141.4 A
--------------------------

2. A sine wave has a frequency of 50 Hz. Its angular frequency is ___________________ radian/second.

A. 100 ㄫ
B. 50 ㄫ
C. 25 ㄫ
D. 5 ㄫ

... Answer is A. 100 ㄫ
----------------------

3. The power factor of a purely resistive circuit is

A. zero
B. unity
C. lagging
D. leading

... Answer is B. unity
---------------------------

4. A capacitor is perfectly insulator for

A. Direct current
B. Alternating current
C. Direct as well as alternating current
D. Induced e.m.f

... Answer is A. Direct current
--------------------------------

5.  The peak value of alternating current is 5√2 A. The mean square value of the current will be

A. 5 A
B. 2.5 A
C. 5√2 A
D. 5² A

... Answer is D. 5² A
------------------------

6. In the choke coil the reactance `\X_L` and resistance R are related as

A. `\X_L` = R
B. `\X_L` ≪ R
C. `\X_L` ≫ R
D. `\X_L` = ∞

... Answer is C. `\X_L` ≫ R
------------------------------

7. The phase difference between the current and voltage at resonance is :

A. 0
B. ㄫ
C. -ㄫ
D. ㄫ/2

... Answer is A. 0
--------------------------

8. In the AC system we generate a sine waveform because

A. It can be easily draw
B. It produces the least disturbance in electrical circuits
C. It is a nature standard
D. Other waves cannot be produced easily.

... Answer is B. It produces the least disturbance in electrical circuits
-------------------------

9. An alternating voltage is given by 20sin 157t. The frequency of alternating voltage is

A. 50 Hz
B. 25 Hz
C. 100 Hz
D. 75 Hz

... Answer is B. 25 Hz
------------------------

10. In LR current which one of the following statements is correct?

A. L and R oppose each other
B. R-value increases with frequency
C. The inductive reactance increases with frequency
D. The inductive reactance decreases with frequency.

... Answer is D. The inductive reactance decreases with frequency.
----------------------

11. An alternating quantity (voltage or current) is completely known if we know it's

A. maximum value
B. frequency and phase.
C. effective value
D. both (a) and (b)

... Answer is B. both (a) and (b)
------------------------------

12. For electromagnetic waves, Maxwell generalized

A. gausses law for magnetism
B. gausses law for electricity
C. faradays law
D. amperes law

... Answer is D. amperes law
-------------------------

13. An electromagnetic wave goes from air to glass which of the following does not change?

A. Radio waves
B. X-rays
C. Ultraviolet radiation
D. Ultrasound waves

... Answer is D. Ultrasound waves
-------------------------

14.  The circuit in which current and voltage are in phase, the power factor

A. Zero
B. 1
C. -1
D. 2

... Answer is B. 1
----------------------------

15. with an increase in the frequency of an AC supply, the impedance of an RLC series circuit

A. remains constant
B. increases
C. decreases
D. capacitive reactance `\X_C` decreases only.

... Answer is B. increases
-----------------------------

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