Current Electricity 5 Question 4
4. A $2 W$ carbon resistor is color coded with green, black, red and brown respectively. The maximum current which can be passed through this resistor is
(2019 Main, 10 Jan I)
(a) $0.4 mA$
(b) $63 mA$
(c) $20 mA$
(d) $100 mA$
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Solution:
- Colour code of carbon resistance is shown in the figure below
So, resistance value of resistor using colour code is
$$ R=502 \times 10=50.2 \times 10^{2} \Omega $$
Here, we must know that for given carbon resistor first three colours give value of resistance and fourth colour gives multiplier value.
Now using power, $P=i^{2} R$
$$ \text { we get, } \quad \begin{aligned} i & =\sqrt{\frac{P}{R}}=\sqrt{\frac{2}{50.2 \times 10^{2}}} \\ & \simeq 20 \times 10^{-3} A=20 mA . \end{aligned} $$
