Question

How will you connect three resistors of $3\Omega$, $4\Omega$ and $7\Omega$ respectively so as to obtain a resultant resistance of $3.5\Omega$?

• A. $3\Omega$, $4\Omega$ and $7\Omega$ in series
• B. $3\Omega$, $4\Omega$ and $7\Omega$ in parallel.
• C. $3\Omega$, and $4\Omega$ in series and then parallel with $7\Omega$.
• D. $3\Omega$, and $4\Omega$ in parallel and then series with $7\Omega$.

Answer 1

The correct option is C

$3\Omega$, and $4\Omega$ in series and then parallel with $7\Omega$.

When $3\Omega$ and $4\Omega$ are in series, we get total resistance, $R_{total}=3+4=7\Omega$
Now $R_{total}$ and $7\Omega$ has to be connected in parallel.

i.e, $\frac{1}{R}=\frac{1}{7}+\frac{1}{7}$ $=3.5\Omega$