DSE Physics: Electricity and Magnetism — Practice Questions & Answers
Electrostatics, current, voltage, resistance and Ohm's law, circuits and power, domestic electricity and safety, magnetic fields and forces, and electromagnetic induction.
384 practice questions available for this topic — here are 10 with full answers and explanations.
A 3 ohm resistor and a 6 ohm resistor are connected in parallel. The equivalent resistance is
2 ohm
9 ohm
4.5 ohm
18 ohm
Tap an answer to check it.
Why1/R = 1/3 + 1/6 = 1/2, so R = 2 ohm.
2Multiple choice · Medium
A cell of e.m.f. 12 V and internal resistance 2 ohm is connected to a 3 ohm resistor and a 6 ohm resistor in parallel. The current in the 6 ohm resistor is
1.0 A
0.5 A
1.5 A
2.0 A
Tap an answer to check it.
WhyParallel = 2 ohm; total = 4 ohm; total current = 3 A; terminal p.d. = 6 V; I(6 ohm) = 6/6 = 1.0 A.
3Multiple choice · Hard
For the same cell (e.m.f. 12 V, internal resistance 2 ohm) with the 3 ohm and 6 ohm resistors in parallel, the power dissipated inside the cell is
18 W
6 W
36 W
12 W
Tap an answer to check it.
WhyTotal current 3 A; internal power = I^2 r = 3^2 x 2 = 18 W.
4Fill in the blank · Easy
The voltage available at the terminals of a cell, after the internal resistance drop, is the voltage.
Answer:
terminal
WhyV = emf - I r is the terminal voltage.
5Fill in the blank · Medium
A cell of e.m.f. 12 V with internal resistance 2 ohm supplies a total current of 3 A. Its terminal voltage is V.
Answer:
6 / 6.0
WhyV = 12 - 3 x 2 = 6 V.
6Fill in the blank · Hard
A cell of e.m.f. 6.0 V and internal resistance 0.5 ohm is connected to an external resistance of 2.5 ohm. The current in the circuit is A.
Answer:
2 / 2.0
WhyI = emf/(R + r) = 6.0/(2.5 + 0.5) = 2.0 A.
7Multiple choice · Easy
An e.m.f. is induced in a circuit whenever
the magnetic flux linking the circuit changes
a constant flux links the circuit
a steady current already flows
the circuit is open
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WhyFaraday's law: a changing magnetic flux linkage induces an e.m.f.
8Multiple choice · Medium
A square metal frame of side L moves at constant velocity v completely through a region of uniform magnetic field of width 5L. The total time during which a current is induced in the frame is
2L/v
L/v
3L/v
4L/v
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WhyFlux changes only as the frame enters (L/v) and leaves (L/v); the total is 2L/v.
9Multiple choice · Hard
A copper rod falls vertically and cuts the horizontal component of a magnetic field, but it is NOT part of a closed circuit. Which statement is correct?
A voltage is induced across the rod but it still falls with acceleration g
A steady current flows in the rod
The rod falls with an acceleration less than g
No voltage is induced across the rod
Tap an answer to check it.
WhyWith no closed circuit no current flows, so there is no opposing force; a voltage is still induced across the ends and the rod falls with acceleration g.
10Fill in the blank · Easy
The induced e.m.f. of a moving straight conductor is given by e.m.f. = B L .
Answer:
v / velocity / speed
WhyMotional e.m.f. = B L v.
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