Question

The sequence of bands in carbon resistor are brown, black, brown and gold, the value of resistance is (in $\Omega $)
(A) Exactly $100$
(B) $95$ to $105$
(C) $90$ to $100$
(D) $80$ to $120$

Answer 1

Hint: Here, you are given a set of four colours and you are asked to find the value of resistance that this resistor will have. In order to proceed, you should use the resistor colour code. The table consists of colours and it tells you the value of resistance. Use the significant digits, multiplier and tolerance columns to find the resistance.

Complete answer:
The first two colours belong to the significant digit column. These colour bands give you the first two digits of the resistance. The third colour band consists of the multiplier. The multiplier shifts the decimal place to change the value representation of the resistor. The fourth colour belongs to the tolerance column. It gives you the tolerance of the resistor, meaning that the value of resistance may vary from that particular given tolerance.

For brown colour, the significant value is $1$, so, the first digit at the left of the value of the resistance will be $1$. For black colour, the significant value is $0$, so, the second digit from left of the value of the resistance will be $0$. Now, for multiplier, we are given the colour brown. The multiplier for brown colour is $10$.

Now, you will multiply the obtained value of resistance from the first two colours by $10$. Finally, the tolerance is given to be gold colour which is $ \pm 5\% $. Therefore, the obtained resistance will be $\left( {10 \times 10} \right) \pm 5\% = 100 \pm 5\% $. So, the value range of resistance will be $95$ to $105$.Therefore, the value of resistance is $95$ to $105$.

Hence,option B is correct.

Note: You should keep in mind the whole resistance colour code table. Remember that the first two colours will give you the first two digits of the value of resistance. Note that if the fourth colour is not given, that is, the tolerance band is not given, then the default tolerance is $ \pm 20\% $. Also do not miss the multiplier, else you will get the wrong value of resistance.