Question

What resistance must be connected in parallel to a $8\Omega$ resistance to make the effective resistance equal to $4.8\Omega$?

• A. $6\Omega$
• B. $7\Omega$
• C. $5\Omega$
• D. $12\Omega$

Answer 1

The correct option is D $12\Omega$

Given:
Value of resistance, $R_1$ = $8\Omega$
Equivalent resistance to be obtained, $R_{eq}$ = $4.8\Omega$
Let the resiatance of the resistor to be connected be $R_2$.
For a parallel combination of resistors,

$R_{eq}=\frac{R_1\times R_2}{R_1+R_2}$

$⟹4.8=\frac{R_2\times 8}{8+R_2}$

$⟹38.4+4.8R_2=8R_2$

$⟹R_2=\frac{38.4}{3.2}=12\Omega$

So, to make an equivalent of $4.8\Omega$, a resistance of $12\Omega$ needs to be connected in parallel to the given resistance.