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Colour Coding of Resistors

In a potentio...

Question

In a potentiometer, the balance length with standard cadmium cell is 509 cm. The emf of a cell which when connected in the place of the standard cell gave a balanced length of 750 cm is (emf of the standard cell is 1.018V):

A

1.5V

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B

0.5V

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C

1.08V

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D

1.2V

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Solution

The correct option is A 1.5V
Let the Emf of cell be E

$\Rightarrow E_{c} = I \times r \times l_{1} [I_{1} = 509 c m]$

r - resistance per unit length of wire

$E = I \times r \times l_{2} [I_{2} = 750 c m]$

$\Rightarrow \frac{E_{c}}{E} = \frac{l_{1}}{l_{2}} = \frac{509}{750}$

$\Rightarrow \frac{1.018}{E} = \frac{509}{750}$

$E = 1.018 \times \frac{750}{509} = 1.5 V$

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