Question

Seven identical lamps of resistance 220 $\Omega$ each are connected to a 220 V line as shown in Fig. Then the reading in the ammeter will be

• A. $\frac{1}{10}A$
• B. $\frac{2}{3}A$
• C. $\frac{3}{10}A$
• D. none of these

Answer 1

The correct option is D none of these

All lamps are in parallel. So equivalent resistance

$\frac{1}{R}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\frac{1}{R_4}+\frac{1}{R_5}+\frac{1}{R_6}+\frac{1}{R_7}C{R}_1=R_2=R_3=R_4=R_5=R_6=R_7{R}_{eq}=\frac{R}{7}$

Total current=$\frac{V}{R_{eq}}=\frac{220}{220}\times 7A=7A$

So 7A passes through the whole circuit then each resistance suffers 1A of current.

Then resistance that are away from ammeter are 5 from which current goes to the ammeter

Then the reading will be 5A.

Hence answer is 5A

Option D is correct.