MCQ
The power loss is less in transmission lines, when:
- AVoltage is less but current is more
- BBoth voltage and current are more
- CVoltage is more but current is less
- DBoth voltage and current are less
Explanation:
The power cables have some resistance.
Power lost in the wires can be calculated as P = I2R with R as the resistance of the wires and I as the current that passes through them.
Power at the load is P = VI.
From this one can see that if voltage is increased by say n times, then only $\frac{1}{\text{n}}$ the current is required to deliver the same power. However, if $\frac{1}{\text{n}}$ current is passed
on the same wires, only $\frac{1}{\text{n}^2}$ of the power will be lost.
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Why the current does not rise immediately in a circuit containing inductance
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(a) Because of induced emf |
(b) Because of high voltage drop |
|
(c) Because of low power consumption |
(d) Because of Joule heating |
A potentiometer consists of a wire of length 4 m and resistance 10Ω. It is connected to a cell of e.m.f. 2 V. The potential difference per unit length of the wire will be
|
(a) 0.5 V/m |
(b) 2 V/m |
(c) 5 V/m |
(d) 10 V/m |
The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately
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(a) 0.230 per minute |
(b) 0.461 per minute |
|
(c) 0.691 per minute |
(d) 0.922 per minute |
Two resistors whose value are in ratio 2 : 1 are connected in parallel with one cell. Then ratio of power dissipated is
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(a) 2 : 1 |
(b) 4 : 1 |
(c) 1 : 2 |
(d) 1 : 1 |