Basic Electrical Engineering MCQs Part 4
Basic Electrical Engineering MCQs Part 4
Contents
If a piece of wire is melted and recast to half of its original length, the new resistance is
If a piece of wire is melted and recast to half of its original length, the new resistance is:
- R
- R/2
- R/4
- 2R
Correct answer: 3. R/4
Explanation:
Suppose R = ρl/A is original resistance
And R’ = ρl’/A’ is new resistance
Since volume of wire remains same
lA = l’A’
A/A’ = l’/l
l’ = 0.5l
Now A/A’ = l’/l = 0.5 = ½
R’R = l’/l * A/A’ = ½ * ½ = ¼
R’ = R/4
The resistance of human body is about:
The resistance of human body is about:
- 1 Ω
- 10 Ω
- 100 Ω
- 1000 Ω
Correct answer: 4. 1000 Ω
A current flow of 10 A for 1 hour will transfer how much charge
A current flow of 10 A for 1 hour will transfer how much charge:
- 3.8 * 10^3 C
- 2.2 * 10^3 C
- 1.5 * 10^2 C
- 3.6 * 10^4 C
Correct answer: 4. 3.6 * 10^4 C
Solution: q = It = 10 A * 3600 s = 36000 As = 3.6 * 10^4 C
The thermal speed of electrons is of the order of
The thermal speed of electrons is of the order of
- 10^-3 m/s
- 10^6 m/s
- 10^8 m/s
- None of these
Correct answer: 2. 10^6 m/s
Due to drop of current by 3%, the percentage by which incandescence of lamp decreases is
Due to drop of current by 3%, the percentage by which incandescence of lamp decreases is:
- 3%
- 6%
- 9%
- 12%
Correct answer: 2. 6%
Explanation:
P = I²R or ΔP = 2I(ΔI)R
ΔP/P = 2ΔI/I = 2 * 3% = 6%