A complete series circuit consists of a 11.9V battery, a 4.73ohm resistor, and a

Question

A complete series circuit consists of a 11.9V battery, a 4.73ohm resistor, and a switch. The internal resistance of the battery is 0.340 ohms.
1. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is open.
2. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is now closed. A complete series circuit consists of a 11.9V battery, a 4.73ohm resistor, and a switch. The internal resistance of the battery is 0.340 ohms.
1. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is open.
2. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is now closed.
1. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is open.
2. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is now closed. 2. What does the ideal voltmeter read when place accross A. the terminals of the battery, B. the resistor, C. The switch when the switch is now closed.

Explanation / Answer

Ideal voltmeter is the device which does not draw any current from the battery
for its function . Ideal voltmeter has very large resistance.
1)
A :
When switch is open ideal voltmeter measures the emf of the battery when placed across the terminals of the battery .
So the answer is 11.9 V

B :
When the switch is open no current passes through the circuit . Hence no potential drop across the resistor .Hence it shows 0 volts and the answer is 0 V

C :
When the switch is open and the leads are kept at the switch then the volt meter reads the emf of the battery.
So the answer is 11.9 V

2)

When the switch is closed , current passes through the circuit given by
I = E/R+r
I = 11.9/(4.73+0.34)=11.9/5.07 = 2.347 A

A :
When the switch is closed , then the volt meter reads the terminal potential difference of the circuit given by
V = E - Ir where r is the internal resistance of the battery .
Hence V = 11.9-(2.347)(0.34) = 11.10 V
Hence the answer is 11.10 V

B :
When the switch is closed , the ideal voltmeter reads the potential difference across the resistor 4.73 V is given by
V = IR = (2.347)(4.73) = 11.10 V
Hence the answer is 11.10 V

C :
When the switch is closed , and if the leads of the ideal volt meter are placed at the ends the switch , then the volt meter shows 0 V
Hence the answer is 0 V

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