Test Index

JAMB Physics 2014 Paper

Question : 31

Total: 41

Solution:

Concept:

To reduce the total resistance of an existing resistor, an additional resistor must be connected in parallel.

Explanation:

Let the unknown resistor be

R

. For parallel combination with the

200\,\Omega

resistor:

\frac{1}{120} = \frac{1}{200} + \frac{1}{R}

\frac{1}{R} = \frac{1}{120} - \frac{1}{200} = \frac{200 - 120}{24000} = \frac{80}{24000}

R = 300\,\Omega

So a

300\,\Omega

resistor must be connected in parallel.

Answer:

A. A 300Ω resistor is connected to it in parallel

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