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:

  1. 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, $P=i^{2} R$

$$ \text { we get, } \quad \begin{aligned} i & =\sqrt{\frac{P}{R}}=\sqrt{\frac{2}{50.2 \times 10^{2}}} \\ & \simeq 20 \times 10^{-3} A=20 mA . \end{aligned} $$



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