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Electricity & Magnetism — Homi Bhabha Exam Physics MCQs with Solutions
Free Homi Bhabha Exam Physics Electricity & Magnetism MCQs with step-by-step solutions covering Electric Charge & Potential Difference, Ohm's Law, Series & Parallel Resistors, Heating Effects of Current, Domestic Circuits, Magnetic Lines of Force. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Electric Charge & Potential Difference · hard · numerical
If 20 J of work is done in moving 4 C of charge between two points, the potential difference between them is:
A. 80 V
B. 5 V ✓ Correct
C. 24 V
D. 0.2 V
Solution: $V = \dfrac{W}{Q} = \dfrac{20}{4} = 5$ V.
Q2 — Ohm's Law · hard · numerical
A current of 0.5 A flows through a 20 Ω resistor. The potential difference across it is:
A. 10 V ✓ Correct
B. 20.5 V
C. 0.025 V
D. 40 V
Solution: $V = IR = 0.5 \times 20 = 10$ V.
Q3 — Ohm's Law · hard · theory
On a graph of potential difference (V) against current (I) for an ohmic conductor, the slope of the straight line gives the:
A. current
B. resistance ✓ Correct
C. charge
D. power
Solution: Since $V = IR$, the V–I graph is a straight line whose slope equals the resistance R.
Q4 — Series & Parallel Resistors · hard · numerical
Two 6 Ω resistors are connected in parallel. Their equivalent resistance is:
A. 6 Ω
B. 12 Ω
C. 36 Ω
D. 3 Ω ✓ Correct
Solution: For two equal parallel resistors, $R = \dfrac{6}{2} = 3$ Ω.
Q5 — Series & Parallel Resistors · hard · numerical
A 2 Ω and a 3 Ω resistor are connected in parallel. The equivalent resistance is:
A. 1.2 Ω ✓ Correct
B. 2.5 Ω
C. 5 Ω
D. 6 Ω
Solution: $\dfrac{1}{R} = \dfrac{1}{2} + \dfrac{1}{3} = \dfrac{5}{6} \Rightarrow R = \dfrac{6}{5} = 1.2$ Ω.
Q6 — Series & Parallel Resistors · hard · numerical
Three 2 Ω resistors are connected in series across a 12 V battery. The current in the circuit is:
A. 18 A
B. 6 A
C. 2 A ✓ Correct
D. 0.5 A
Solution: Total resistance $= 2 + 2 + 2 = 6$ Ω; current $= \dfrac{12}{6} = 2$ A.
Q7 — Heating Effects of Current · hard · numerical
An electric device draws a current of 0.5 A at 220 V. Its power consumption is:
A. 110 W ✓ Correct
B. 55 W
C. 220.5 W
D. 440 W
Solution: Power $= V \times I = 220 \times 0.5 = 110$ W.
Q8 — Heating Effects of Current · hard · theory
An electric fuse protects a circuit because, when the current becomes too large, the fuse wire:
A. cools the circuit
B. stores the charge
C. melts and breaks the circuit ✓ Correct
D. increases the current
Solution: Excess current heats the low-melting fuse wire until it melts, breaking the circuit and preventing damage.
Q9 — Domestic Circuits · hard · theory
The earth wire in a domestic circuit is provided mainly for:
A. safety, by carrying leakage current to the ground ✓ Correct
B. supplying current to appliances
C. increasing the voltage
D. reducing the bill
Solution: The earth wire safely diverts any leakage current to the ground, protecting the user from shock.
Q10 — Domestic Circuits · hard · theory
For safety, the fuse (or MCB) in a household circuit is always connected in the:
A. neutral wire
B. appliance body
C. earth wire
D. live wire ✓ Correct
Solution: The fuse is placed in the live wire so that, when it blows, the appliance is disconnected from the live supply.
Q11 — Magnetic Lines of Force · hard · theory
Two magnetic field lines can never intersect each other because:
A. field lines are straight
B. at the point of intersection there would be two directions of the field, which is impossible ✓ Correct
C. they repel each other
D. the field is zero there
Solution: A single point can have only one net field direction, so field lines cannot cross.
Q12 — Motors & Generators · hard · theory
The working of an electric generator is based on the principle of:
A. conservation of charge
B. electromagnetic induction ✓ Correct
C. Ohm's law
D. the heating effect of current
Solution: A changing magnetic flux through the coil induces an EMF — electromagnetic induction (Faraday's law).
Q13 — Electric Charge & Potential Difference · medium · theory
The SI unit of electric charge is the:
A. volt
B. ampere
C. ohm
D. coulomb ✓ Correct
Solution: Charge is measured in coulombs (C); 1 C = 1 ampere × 1 second.
Q14 — Electric Charge & Potential Difference · medium · numerical
If a current of 2 A flows through a wire for 5 s, the charge that passes through it is:
A. 10 C ✓ Correct
B. 2.5 C
C. 0.4 C
D. 7 C
Solution: Charge $Q = I \times t = 2 \times 5 = 10$ C.
Q15 — Electric Charge & Potential Difference · medium · theory
The potential difference between two points is defined as the work done in moving a unit charge between them, and its SI unit is the:
A. coulomb
B. watt
C. ampere
D. volt ✓ Correct
Solution: Potential difference $V = \dfrac{W}{Q}$; its unit is the volt (1 V = 1 J/C).
Q16 — Electric Charge & Potential Difference · medium · theory
A material through which electric charge flows easily is called a:
A. insulator
B. conductor ✓ Correct
C. dielectric
D. semiconductor only
Solution: Conductors (e.g. metals) allow charge to flow; insulators (e.g. rubber) resist it.
Q17 — Ohm's Law · medium · theory
Ohm's law states that, at constant temperature, the current through a conductor is:
A. independent of the potential difference
B. inversely proportional to the potential difference
C. proportional to the square of the voltage
D. directly proportional to the potential difference across it ✓ Correct
Solution: $V = IR$, so $I \propto V$ at constant temperature and resistance.
Q18 — Ohm's Law · medium · numerical
A potential difference of 12 V is applied across a 4 Ω resistor. The current through it is:
A. 48 A
B. 0.33 A
C. 3 A ✓ Correct
D. 16 A
Solution: $I = \dfrac{V}{R} = \dfrac{12}{4} = 3$ A.
Q19 — Ohm's Law · medium · numerical
A current of 2 A flows through a resistor when 10 V is applied across it. Its resistance is:
A. 5 Ω ✓ Correct
B. 12 Ω
C. 0.2 Ω
D. 20 Ω
Solution: $R = \dfrac{V}{I} = \dfrac{10}{2} = 5$ Ω.
Q20 — Series & Parallel Resistors · medium · numerical
Three resistors of 2 Ω, 3 Ω and 5 Ω are joined in series. Their combined resistance is:
A. 10 Ω ✓ Correct
B. 1 Ω
C. 0.97 Ω
D. 30 Ω
Solution: In series, resistances add: $2 + 3 + 5 = 10$ Ω.
Q21 — Series & Parallel Resistors · medium · theory
In a series circuit, the quantity that is the same through every component is the:
A. potential difference
B. resistance
C. current ✓ Correct
D. power
Solution: In series the same current flows through all components, while the voltage divides among them.
Q22 — Heating Effects of Current · medium · theory
The heat produced in a resistor carrying a current is given by Joule's law of heating:
A. $H = I^2 R$
B. $H = I R t$
C. $H = I^2 R t$ ✓ Correct
D. $H = \dfrac{I t}{R}$
Solution: Joule's law: $H = I^2 R t$ — heat depends on the square of the current.
Q23 — Heating Effects of Current · medium · theory
Which of the following appliances works mainly on the heating effect of electric current?
A. Loudspeaker
B. Electric bell
C. Electric iron ✓ Correct
D. Electric fan
Solution: An electric iron (like heaters and geysers) uses the heat produced when current passes through a resistance wire.
Q24 — Domestic Circuits · medium · theory
The voltage of the domestic electricity supply in India is about:
A. 220 V ✓ Correct
B. 1000 V
C. 12 V
D. 5 V
Solution: Indian household supply is about 220 V AC at 50 Hz.
Q25 — Domestic Circuits · medium · theory
Electrical appliances in a house are connected in parallel so that:
A. each gets the full supply voltage and can be switched on/off independently ✓ Correct
B. only one can work at a time
C. they share the voltage
D. the current is the same in all
Solution: Parallel connection gives every appliance the full 220 V and independent operation.
Q26 — Magnetic Lines of Force · medium · theory
Outside a bar magnet, the magnetic field lines are directed from the:
A. north pole to the north pole
B. south pole to the north pole
C. north pole to the south pole ✓ Correct
D. centre to the poles
Solution: By convention, field lines emerge from the north pole and enter the south pole outside the magnet.
Q27 — Magnetic Lines of Force · medium · theory
The magnetic field is strongest where the field lines are:
A. farthest apart
B. straight
C. parallel
D. closest together (most crowded) ✓ Correct
Solution: The density of field lines indicates field strength; crowded lines mean a stronger field.
Q28 — Magnetic Lines of Force · medium · theory
A small compass needle placed in a magnetic field comes to rest:
A. in a random direction
B. along the direction of the field ✓ Correct
C. perpendicular to the field
D. pointing vertically down
Solution: The compass needle aligns itself along the local direction of the magnetic field.
Q29 — Motors & Generators · medium · theory
An electric motor converts:
A. electrical energy into mechanical energy ✓ Correct
B. electrical energy into chemical energy
C. mechanical energy into electrical energy
D. heat into electrical energy
Solution: A motor uses the force on a current-carrying coil in a magnetic field to produce rotation (mechanical energy).
Q30 — Motors & Generators · medium · theory
An electric generator (dynamo) converts:
A. chemical energy into heat
B. light into electricity
C. electrical energy into mechanical energy
D. mechanical energy into electrical energy ✓ Correct
Solution: A generator rotates a coil in a magnetic field to induce a current — mechanical to electrical energy.