Question Guide – DC Circuit

This question is related to the topic “DC Circuit” in O Level Physics tuition.

Question:
A resistor of resistance 2.0 Ω is connected across a series of cells of e.m.f. 9.0 V by wires of negligible resistance. A current 4.0 A passes through the resistor. Calculate
(a) The power dissipated in the resistor,
(b) The total power produced by the cells,
(c) State a reason for the difference in values in (a) and (b).
(a) The power dissipated in the resistor,
Solution:
O Level Physics DC Circuit Power is I square R
(b) The total power produced by the cells,
Solution:
O Level Physics DC Circuit Power is IV
(c) State a reason for the difference in values in (a) and (b).
Observation:
If total resistance is just 2 Ω, circuit current
O Level Physics DC Circuit Current
But the actual current is lower i.e. 4.0 A. This shows that the

total circuit resistance is actually higher than 2 Ω.

Typically, the cells have significant internal resistance. Thus, the higher circuit resistance.
Solution:
Some power is dissipated in the internal resistance of the cells.

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Sample Question and Solution on DC Circuit ultima modifica: 2017-10-18T07:10:35+00:00 da LearningForKeeps