Basic Electrical Engineering MCQs Part 13
Contents
- 1 EMF in a circuit
- 2 A copper wire of resistance Ro is stretched till its length is increased n times of its original length. Its resistance will become
- 3 Certain resistor develops 1000 J of thermal energy in 10 s when a current of 10 A is passed through it. The resistance of resistor is
- 4 A copper wire having area of cross section 5 mm² is 5 meters long and carries a current of 5 A. The number density of free electrons is 8E+28. The time required by an electron to travel the length of wire is
- 5 Two electric bulbs rated for same voltage have powers of 100 W and 200 W. If their resistances are R1 and R2, then which of following relationship is correct
EMF in a circuit
EMF in a circuit:
- Maintains the potential difference
- Decreases resistance of circuit
- Increases resistance of circuit
- None of these
Correct answer: 1. Maintains the potential difference
A copper wire of resistance Ro is stretched till its length is increased n times of its original length. Its resistance will become
A copper wire of resistance Ro is stretched till its length is increased n times of its original length. Its resistance will become:
- nRo
- n^2Ro
- Ro/n
- Ro/n^2
Correct answer: 2. n^2Ro
Certain resistor develops 1000 J of thermal energy in 10 s when a current of 10 A is passed through it. The resistance of resistor is
Certain resistor develops 1000 J of thermal energy in 10 s when a current of 10 A is passed through it. The resistance of resistor is:
- 0.5 Ω
- 1 Ω
- 2 Ω
- 5 Ω
Correct answer: 2. 1 Ω
Solution:
Energy = I² Rt
R = Energy/I²t
R = 1000 J /(10² * 10 ) = 1 Ω
A copper wire having area of cross section 5 mm² is 5 meters long and carries a current of 5 A. The number density of free electrons is 8E+28. The time required by an electron to travel the length of wire is
A copper wire having area of cross section 5 mm² is 5 meters long and carries a current of 5 A. The number density of free electrons is 8E+28. The time required by an electron to travel the length of wire is:
- 14.32 h
- 17.77 h
- 25.96 h
- 32.33 h
Correct answer: 2. 17.77 h
Solution:
Charge on electron = 1.6*10^-19
Drift velocity = I/nAe = 0.000078125 m/s
Time taken by electron to travel length of wire
t = Length/Drift velocity = 64000 s = 17.77 h
Two electric bulbs rated for same voltage have powers of 100 W and 200 W. If their resistances are R1 and R2, then which of following relationship is correct
Two electric bulbs rated for same voltage have powers of 100 W and 200 W. If their resistances are R1 and R2, then which of following relationship is correct:
- R1 = R2
- R1 = 2R2
- R1 = 0.5 R2
- None of these
Correct answer: 2. R1 = 2R2
Solution:
R1 = V^2 / 100
R2 = V^2 / 200
R2/R1 = 100/200 = 0.5
Or R1 = 2R2