A wire of 5Ω resistance is drawn out so that its ne...
A wire of 5Ω resistance is drawn out so that its new length is two times the original length. If the resistivity of the wire remains the same and the cross-sectional area is halved, the new resistance is
40Ω
20Ω
10Ω
5Ω
Correct answer is B
Let the original length = L1
Let the original resistance = R1 = 5Ω
Let the original resistivity = P1
Let the original area = a1
Let the new length = L2 = 2L1
let the new area = a2 = 1/(2a2)
Let the new resistance = R2
Let the new resistivity = P2
But since the resistivity remains the same,
=> P1 = P2
| ∴ P1 = | R1 a1 |
| _L1 |
| = P2 = | R2 a2 |
| _L2 |
| ∴ | R1 a1 |
| _L1 |
| = | R2 2a1/2 |
| _2L1 |
| => | 5 x a1 |
| _L1 |
| = | R2 x a1 |
| _4L1 |
| ∴R2 = | 5 x a1 x 4L1 |
| _a1 x L1 |
A device that converts mechanical energy into electrical energy is ...
A block of ice of mass 10kg at 0°C absorbs heat energy from its surroundings and changes to wate...
Which of the following operations does not represent an action of a force field? ...
Which of the following are contact forces? I. Force of tension II. Force of fiction, III. Magne...
The main reason why rice cooks faster in a pressure cooker than in cooking pot is that ...
At different locations on the earth's surface, the earth's magnetic field is ...