A 3V battery of internal resistance 1 ohm is joined to a sliding wire of length 100cm and resistance 5 ohm. A voltmeter, which takes negligible current, is connected across 60cm length of the wire. What is the reading of the voltmeter? if the resistance of the voltmeter were 150 ohm then what would have been its reading?
Answers
Answer:
1.5 V
1.485 V
Explanation:
A 3V battery of internal resistance 1 ohm is joined to a sliding wire of length 100cm and resistance 5 ohm. A voltmeter, which takes negligible current, is connected across 60cm length of the wire. What is the reading of the voltmeter? if the resistance of the voltmeter were 150 ohm then what would have been its reading?
Battery Voltage = 3 V
Internal Resistance = 1 Ω
100 cm Wire resistance = 5 Ω
So current in Circuit = I
3 - I*1 = I 5
=> 3 = 6I
=> I = 0.5A
60 cm Wire resistance = (60/100) * 5 = 3 Ω
Voltage across 3 Ω = 3 * 0.5 = 1.5 V
reading of the voltmeter = 1.5V
if resistance of the voltmeter were 150 Ω
Parallel resistance between 3 Ω & 150 Ω
= 1/(1/3 + 1/150) = 150/51 Ω
Total Resistance = 1 + 150/51 + 2 = 303/51 Ω
Total current through circuit = 3/(303/51) = 51/101 A
Voltmeter reading = (51/101 ) * (150/51)
= 150/101
= 1.485 V