Q. 17

# The potential difference between the terminals of a battery of emf 6.0 V and internal resistance 1 Ω drops to 5.8 V when connected across an external resistor. Find the resistance of the external resistor.

Answer :

29Ω

Given,

The emf of the cell, E=6V

The value of internal resistance, r= 1 Ω

The volt meter reading across the setup, V=5.8V

The value of external resistance= R Ω

Formula used:

Figure shows the overview of the setup.

The voltage across the cell will be equal to that across the external resistance. So,

Solution:

The current flowing through the internal and external resistance are the same.

By substituting the given values in the eqn.1, we get i as

Or,

Or,

This current also circulate through the external resistance R. Hence from the eqn.1, we can write its expression as,

By substituting the values of ‘i’ and V, we get

Or,

Hence the resistance of the external resistor is 29Ω.

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The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell?

Physics - Board Papers

Draw a circuit diagram of a potential divider using a cell and a rheostat. Also mark the output terminals.

Physics - ExemplarConsider a capacitor-charging circuit. Let Q_{1} be the charge given to the capacitor in a time interval of 10 ms and Q_{2} be the charge given in the next time interval of 10ms. Let 10μC charge be deposited in a time interval t_{1} and the next 10 μC charge is deposited in the next time interval t_{2}.