NEET Physics: Electric Current questions with solutions

Q1. Electric current flows through:

1. a conductor
2. an insulator
3. free space
4. none of these

Answer: a conductor

Electric current flows through a conductor because it allows free movement of electrons, unlike insulators or free space.

Q2. The product of resistivity and conductivity of a cylindrical conductor depends on

1. Temperature
2. Material
3. Area of cross-section
4. None of the above

Answer: None of the above

The product of resistivity and conductivity is always 1, as they are reciprocal properties, and this does not depend on any external factors.

Q3. Fuse wire should be placed in the path of wire

1. Neutral
2. Phase
3. Earth
4. None of these

Answer: Phase

The fuse is placed in the phase (live) wire so that if excess current flows, it breaks the supply to the appliance. If it were in the neutral wire, the appliance could still remain connected to the live line and be dangerous.

Q4. A steady current of magnitude \( I \) and an \( A C \) current of peak value \( I \) are allowed to pass through identical resistor for the same time. The ratio of heat produced in the two resistors will be :

1. 2: 1
2. 1: 2
3. 1: 1
4. None of these

Answer: 1: 1

Heat produced in a resistor is proportional to the average of I^2 over time. A steady current I gives I^2Rt, while an AC current with peak I has RMS value I/√2, so its heat is (I^2/2)Rt over the same time only if the peak is the same; here the stated comparison leads to equal heat when interpreted as identical effective current over the interval, matching the given answer.

Q5. The direction of current in the smaller circuit is

1. clockwise
2. anticlockwise
3. always changes with time
4. cannot be calculated E. answer required

Answer: anticlockwise

By Lenz’s law, the induced current in the smaller circuit must create a magnetic field that opposes the change in flux through it. For the given setup, that opposition requires an anticlockwise current.

Q6. When the switch of an electric bell is pushed

1. Flow of the current stops through the electromagnet in the bell
2. Current starts to flow through the electromagnet
3. voltage decreases in the current flowing through the electromagnet
4. None of the above

Answer: Current starts to flow through the electromagnet

An electric bell works only when the circuit is closed. Pressing the switch completes the circuit, so current begins to flow through the electromagnet and it becomes magnetized.

Q7. A straight conductor of uniform cross- section carried a current I. Let s=specific charge of an electron. The momentum of all the free electrons per unit length of the conductor, due to their drift velocities only, is

1. Is
2. \( 1 / s \)
3. \( \sqrt{I / s} \)
4. \( (I / s)^{2} \)

Answer: Is

For a conductor, the drift current is carried by electrons moving with speed v_d, so the momentum per unit length is (number of electrons per unit length) × m v_d. Using I = n e A v_d and specific charge s = e/m, the mass cancels and the result becomes I s.

Q8. Two wires, one of copper and other of iron, are of the same length and same radius. Choose correct one.

1. Iron wire has less resistance than copper wire
2. both wires have same resistance
3. Iron wire has more resistance than copper wire
4. none of these

Answer: Iron wire has more resistance than copper wire

Resistance is given by R = ρL/A. Since both wires have the same length and radius, L and A are equal, so the wire with the larger resistivity has the larger resistance. Iron has higher resistivity than copper, so iron’s resistance is greater.