Internal Resistance

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A cell of EMF 12 V and internal resistance 2 Ω is connected to an external resistance of 10 Ω. What is the terminal voltage?

RankGuru · Accepted Answer

1. **Determine Total Current ($I$)**: The circuit consists of the external resistor $R$ and internal resistor $r$ in series.
   - $I = \frac{E}{R + r} = \frac{12}{10 + 2} = \frac{12}{12} = 1 	ext{ A}$.
2. **Voltage Drop across Internal Resistance**: $v = I 	imes r = 1 	ext{ A} 	imes 2 	ext{ } \Omega = 2 	ext{ V}$.
3. **Calculate Terminal Voltage ($V$)**: This is the potential difference that reaches the outside circuit.
   - $V = E - Ir = 12 - 2 = 10 	ext{ V}$.
4. **Alternative Method**: $V = I 	imes R = 1 	ext{ A} 	imes 10 	ext{ } \Omega = 10 	ext{ V}$.

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Terminal voltage V of cell with emf E and internal resistance r delivering current I?

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