Question

Find equivalent resistance between A & B in the circuit is

• A. 18 $\Omega$
• B. 8.5 $\Omega$
• C. 16.5 $\Omega$
• D. 49 $\Omega$

Answer 1

The correct option is C

16.5 $\Omega$

Since $12\Omega \&18\Omega$ are in series & we know,
For series connection, $R_{eq}=R_1+R_2+R_3+........+R_n$
$\therefore$ We can substitute $(12\Omega +18\Omega )as30\Omega .$
Now, $30\Omega \&10\Omega$ are in parallel & we know,
For parallel $\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+........+\frac{1}{R_n}$
$\therefore \frac{1}{R}=\frac{1}{30}+\frac{1}{10}=\left(\frac{1+3}{30}\right)\frac{1}{R}=\frac{4}{30}R=\frac{30}{4}=7.5$
Now $9\Omega \&7.5\Omega$ are in series & we know,
for series $R_{eq}=R_1+R_2+R_3+........+R_n$
$\therefore R_{eq}=9+7.5=16.5$