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A 2W carbon resistor is colour-coded with green, black, red and brown respectively. The maximum current which can be passed through this resistor is
(A) 63mA
(B) 0.4mA
(C) 100mA
(D) 20mA

Answer
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Hint
To find the maximum current passing through the resistor, we need to first calculate the value of the resistance using the colour codes. Then, we have to apply the formula P=I2R we can get the value of current.
Formula used: In this solution we will be using the following formula,
P=I2R
Where, P is power, I is the current flowing, and R is the resistance.

Complete step by step answer
The table for the colour codes for carbon is:

LETTERS COLOURFIGUREMULTIPLIER
BBlack 0100
BBrown1101
RRed2102
OOrange3103
YYellow4104
GGreen5105
BBlue6106
VViolet7107
GGrey8108
Wwhite9109

Now, it is given in the question that the power of the carbon resistor is 2W. It is colour coded with green, black, red, and brown.
According to the table, green is 5, black is 0, red is 102
So we get the resistance as R=50×102Ω
In the relation,
P=I2R
From here we can rearrange this formula as,
I2=PR
On taking root, I=PR
If I is maximum, then the resistance should be minimum. Thus,
Rmin=50×102Ω ,
Thus, when we apply the values of R and P in the given formula,
We get,
Imax=PR
Substituting the values we get
Imax=250×102
When we simplify, we get
Imax=2×102A
We can write this in milli-ampere as,
Imax=20mA
Thus, we get the maximum current which can be passed through the resistor is 20mA.
Hence, the correct answer is option (D).

Note
In the colour code for the resistor, we are given four colours. The fourth colour given as brown indicates the tolerance of the material. The colour brown means that the tolerance of that resistor is ±1%.
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