12th class (Fsc) Physics unit 5 MCQs
chapter 5 MCQs 12th Class physics
Alternating Current:
1. In RLC series circuit, the condition for resonance is:
a. Z>Xc
b. XL <Xc
c. XL =Xc
d. XL >Xc
2. When an inductor comes close to a metallic object, its inductance is:
a. Becomes half
b. Decreased
c. Becomes 4 times
d. Increased
3. The combined effect of resistance and reactance is known as:
a. Resistance
b. Inductance
c. Impedance
d. Conductance
4. The slope of q-t curve at any instant of time gives:
a. Current
b. Voltage
c. Charge
d. Both A and B
5. Main reason for worldwide use of A.C is:
a. It is cheaper
b. Transmitted
c. Both A and B
d. Reaches in short time
6. The highest value reached by the voltage or current in one cycle is called:
a. Instantaneous value
b. Peak to peak value
c. Root mean square value
d. Peak value
7. During each cycle A.C voltage reaches a park value:
a. Thrice
b. Once
c. Four time
d. Twice
8. The impedance of RLC series circuit at resonance is given by:
a. Z=R
b. Z= √R2 (X1-Xc)2
c. Z= √R2 + X2c
d. Z= √R2 + X21
9. The impedance Z can be expressed as:
a. Z=I+V
b. Z = Vrms / lrms
c. Z=I-V
d. Z = Vrms / lrms
10. The mean value of A.C in a cycle is:
a. Io
b. 1
c. Io / √2
d. 0
11. When 10V are supplied to an A.C circuit, the current flowing in it is 100mA. It impedance is:
a. 1000Ω
b. 100Ω
c. 1Ω
d. 10Ω
12. The phase angle of a series RLC circuit at resonant frequency is:
a. Zero
b. π/2
c. π/4
d. π
13. The main use of A.C is:
a. Stepping up to required voltage only
b. Minimum line losses
c. Stepping down to required voltage only
d. Long distance transmission
14. During each cycle, the alternate voltage reaches a peak value:
a. Thrice
b. Once
c. Four times
d. Twice
15. The waveform of alternating voltage is a :
a. Tangent curve
b. Cotangent curve
c. Sine cure
d. Cosine cure
16. In R.L series circuit phase angle is given by:
a. θ = tan-1 R/ꞷL
b. θ = tan-1 1/ꞷLR
c. θ = tan-1 ꞷL/R
d. θ = tan-1 ꞷLR
17. Power dissipated in a pure inductor is:
a. Infinite
b. Large
c. Zero
d. Small
18. The frequency of A.C sources used in Pakistan is:
a. 45HZ
b. 50HZ
c. 70HZ
d. 60HZ
19. Average value of current and voltage over a complete cycle is:
a. Zero
b. Positive
c. Infinite
d. Negative
20. The power factor in A.C circuit is:
a. tanΦ
b. sinΦ
c. cotΦ
d. cosΦ
21. The expression P=VI holds only when current and voltage are:
a. At right angle to each other
b. In phase
c. At angle of 120o
d. Out of phase
22. The most common source of an A.C voltage is:
a. Generator
b. Motor
c. Thermocouple
d. Cell
23. The reactance Xc of capacitor is given by:
a. Xc = 1/2πfC
b. Xc2πfC
c. Xc = 1/2πf
d. XcπfC
24. The peak value of A.C source is 20A, then its rms value will be:
a. 20A
b. 14.1A
c. 28.2A
d. 10A
25. Which consumes small power?
a. Resistor
b. Inductor
c. Inductor
d. All of them