Q#804: [Current of Electricity] (Past Exam Paper – November 2010 Paper 12 Q32)
A high-resistance voltmeter connected across battery reads 6.0 V.
When battery is connected in series with a lamp of resistance of 10 Ω, the voltmeter reading falls to 5.6 V.
Which statement explains this observation?
A The electromotive force (e.m.f.) of the battery decreases because more work is done across its internal resistance.
B The e.m.f. of the battery decreases because work is done across the lamp.
C The potential difference (p.d.) across the battery decreases because more work is done across its internal resistance.
D The p.d. across the battery decreases because work is done across the lamp.
Solution 804:
Answer: C.
‘A high-resistance voltmeter connected across battery reads 6.0 V.’
This gives the e.m.f. of the battery. e.m.f. = 6.0V. The e.m.f. is a property of the battery – it does not increase or decrease. [A and B are incorrect]
The potential difference across a battery (difference in potential between the 2 terminals of the battery) is equal to its e.m.f. if its internal resistance is zero.
‘When battery is connected in series with a lamp of resistance of 10 Ω, the voltmeter reading falls to 5.6 V.’
This means that there is some lost volts in the battery, which is due to its internal resistance. Since there is some internal resistance, the p.d. across the battery is not equal to its e.m.f. The potential difference (p.d.) across the battery decreases because more work is done across its internal resistance.
Post a Comment for "A high-resistance voltmeter connected across battery reads 6.0 V. When battery is"