First slide

Electrical measuring instruments

Question

The length of a potentiometer wire is 1200cm and it carries a current of 60mA. For a cell of emf 5V and internal resistance of 20 $Ω$ , the null point on it is found to be at 1000cm. the resistance of whole wire is:

Moderate

A

80 $Ω$
B

120 $Ω$
C

60 $Ω$
D

100 $Ω$

Solution

Null point at 1000 cm means , potential across 1000 cm is 5V.
Let say potential across 1200 cm is $V_{p}$
Thus, potential gradient = $\frac{5}{1000} = \frac{V_{p}}{1200}$ $\Rightarrow V_{P} = 6 V$
Now, use Ohm's Law across the whole wire,
$R_{P} = \frac{V_{P}}{I} = \frac{6}{60 \times 10^{- 3}} = 100 Ω$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App