Question

A 2W carbon resistor is color coded with green, black, red and brown respectively. The maximum current which can be passed through this resistor is:-
(1) 63mA
(2) 0.4mA
(3) 100mA
(4) 20mA

Answer 1

Hint: To find the maximum current which can be passed through this resistor find we have to find the value of resistance. It can be determined by using the color code of the resistor. Then we have to apply the formula of power which is the product of the square of current and resistance.

Formula used:
We know that the formula for power is,
$P={{I}^{2}}R$
Where I is the current flowing through the resistor
R is the resistance

Complete step by step answer:
Given that the carbon resistor is color coded with green, black, red and brown.
Hence the value of resistor using color coding is,
$R=50\times {{10}^{2}}\Omega $
Then by using the relation,
$P={{I}^{2}}R$
Therefore rearranging the equation we get,
${{I}^{2}}=\dfrac{P}{R}$
$\Rightarrow {{I}_{\max }}=\sqrt{\dfrac{P}{R}}$
Given that power,
$P=2W$
Thus by substituting the values we get,
${{I}_{\max }}=\sqrt{\dfrac{2}{50\times {{10}^{2}}}}$
And simplifying the equation becomes,
${{I}_{\max }}=20mA$
Thus the maximum current which can be passed through this resistor is 20mA.
Therefore the correct option is option (D).

Note: While calculating the value of resistance using the color code the last or the fourth ring indicates the tolerance of the material. And the color of the first three rings indicates the value of resistance of the resistor.