Draw a labelled circuit diagram of a potentiometer to measure internal resistance of a cell. Write the working formula. (Derivation not required). 

Explanation

### Step-by-Step Solution:

1. **Draw the Circuit Diagram**:
- Start by drawing a battery (E) which represents the cell whose internal resistance (r) we want to measure.
- Connect a key (K1) in series with the battery.
- Next, connect a rheostat (R) in series to control the current.
- Draw a long wire representing the potentiometer, which is connected to the other end of the rheostat.
- At a certain point along the wire, connect a jockey (J) that can slide along the wire.
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