Question

An ideal ammeter (zero resistance) and an ideal voltmeter (infinite resistance) are connected as shown in fig. The ammeter and the voltmeter readings are

• A. 6.25 A, 3.75 V
• B. 0.00 A, 20 V
• C. 3.00 A, 3.75 V
• D. 6.00 A, 6.25 V

Answer 1

Answer: (B)

0.00 A, 20 V

From given figure the equivalent resistance R of the combination is
$R=(\frac{5\times 15}{5+15}+1.25)$
$R=\frac{75}{20}+1.25$
$R=3.75+1.25$
$\therefore R=5\Omega$
Hence the current I through the circuit is
$I=\frac{20}{5}A=4A$
Now, current through $5\Omega$ resistance is
$\frac{15}{20}\times 4=3A$
Also reading of voltmeter $V_r$(say) is equal to the potential drop across $1.25\Omega$ resistance
$V_r=4\times 1.25V=5V$