First slide

Electrical power

Question

A 5 watt, 10 volt bulb is connected to a cell of emf 10 volt and internal resistance $5 Ω$ . Then power consumed by the bulb is

Moderate

A

4 W
B

2.5 W
C

3.2 W`
D

4.25 W

Solution

R = resistance of bulb $= \frac{10^{2}}{5} Ω = 20 Ω$
Current through the bulb, $i = \frac{10}{20 + 5} A = \frac{2}{5} A$
$∴$ Power consumed by the bulb, $P = {(\frac{2}{5})}^{2} \times 20 W = 3.2 W$

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