When the ammeter reads 7 A, the voltmeter reads
A) 2.8 V with Y at the higher potential.
B) 2.8 V with X at the higher potential.
C) 34 V with Y at the higher potential.
D) 34 V with X at the higher potential.
E) 60 V with X at the higher potential.

Question

When the ammeter  reads 7 A, the voltmeter  reads
A) 2.8 V with Y at the higher potential. 
B) 2.8 V with X at the higher potential. 
C) 34 V with Y at the higher potential. 
D) 34 V with X at the higher potential. 
E) 60 V with X at the higher potential.

Quizplus · Accepted Answer

Using Kirchhoff's laws, the voltage drop across the 10 ohm resistor must equal the voltage drop across the 5 ohm resistor. Let V be the voltage at point X with respect to Y. Then, the voltage across the 10 ohm resistor is 7A*10ohms = 70 V and the voltage across the 5 ohm resistor is 7A*5ohms = 35V. Therefore, we get:
70V - V = V - 35V
Solving for V gives V = 52.5V. 
Now, since the voltmeter is connected from X to Y, it will read the potential difference between these points, which is 52.5V - 18.5V = 34V. The voltmeter will show the higher potential point, which is point Y. Therefore, the answer is C.

When the Ammeter Reads 7 A, the Voltmeter