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 |
Emission spectra are caused by ...
The magnification of an object 2cm tall when placed 10cm in front of a plane mirror is ...
A cell can supply current of 0.8A and 0.4A through a 2Ω and a 3Ω resistors respectively....
Which of the following can conduct electricity owing to the presence of free mobile electrons? ...
For semi conductor to have negative temperature coefficient of resistance implies that ...
Which of the following is not a property of longitudinal waves? ...