Chapter: Magnetic Effect of Electric Current

3. What happens to the magnetic field inside a solenoid if the current through it is doubled?

a) It remains the same

b) It is doubled

c) It is halved

d) It becomes zero

Answer: b) It is doubled
Explanation: The magnetic field inside a solenoid is directly proportional to the current passing through it.



4. The force on a current-carrying conductor placed in a uniform magnetic field is zero when:

a) The conductor is parallel to the field

b) The conductor is perpendicular to the field

c) The angle between the conductor and field is 45°

d) The field is non-uniform

Answer: a) The conductor is parallel to the field
Explanation: When the conductor is parallel to the magnetic field, the force experienced by the conductor is zero as the sine of the angle is zero (F = BIL sinθ).



5. Two long, straight, parallel wires carry currents in the same direction. The magnetic field produced at a point midway between the wires will be:

a) Zero

b) Maximum

c) In the direction of current

d) Opposite to the current

Answer: a) Zero
Explanation: The magnetic fields due to the currents in the two wires will cancel each other out midway between the wires.



6. A proton moving perpendicularly to a uniform magnetic field experiences a force. The direction of the force can be determined using:

a) Fleming’s left-hand rule

b) Fleming’s right-hand rule

c) Right-hand thumb rule

d) Ampere’s law

Answer: a) Fleming’s left-hand rule
Explanation: Fleming’s left-hand rule helps to determine the direction of force on a charged particle moving in a magnetic field.



7. A loop of wire is moved parallel to a magnetic field. What happens to the induced current in the loop?

a) Current is induced

b) No current is induced

c) Current is maximum

d) Current changes direction

Answer: b) No current is induced
Explanation: According to Faraday’s law, no current is induced when the loop moves parallel to the field lines since there is no change in magnetic flux.



8. The magnetic field inside a long, straight current-carrying wire is:

a) Zero

b) Uniform and radial

c) Strong and uniform

d) Circular

Answer: a) Zero
Explanation: Inside a current-carrying wire, there is no enclosed current to produce a magnetic field.



9. A circular loop of wire lies in the plane of the paper. A magnetic field is directed into the plane of the paper. If the current in the loop is in the clockwise direction, the direction of the force on the loop is:

a) Into the paper

b) Out of the paper

c) Radially inward

d) Radially outward

Answer: d) Radially outward
Explanation: The force due to the interaction of the current with the magnetic field causes the loop to experience a radially outward force.



10. The device that converts electrical energy into mechanical energy is:

a) Galvanometer

b) Electric motor

c) Electric generator

d) Ammeter

Answer: b) Electric motor
Explanation: An electric motor works on the principle of the magnetic effect of current to convert electrical energy into mechanical energy.



11. In an electromagnetic wave, the direction of propagation is:

a) Parallel to the electric field

b) Parallel to the magnetic field

c) Perpendicular to both the electric and magnetic fields

d) Opposite to the magnetic field

Answer: c) Perpendicular to both the electric and magnetic fields
Explanation: In an electromagnetic wave, the electric field, magnetic field, and direction of propagation are mutually perpendicular.



12. The frequency of electromagnetic induction is directly proportional to:

a) The strength of the magnetic field

b) The rate of change of magnetic flux

c) The length of the conductor

d) The angle between the field and the conductor

Answer: b) The rate of change of magnetic flux
Explanation: According to Faraday’s law, induced emf depends on the rate of change of magnetic flux.



13. What is the nature of the magnetic field inside a toroidal solenoid?

a) Uniform outside, zero inside

b) Circular inside, zero outside

c) Uniform both inside and outside

d) Radially inward

Answer: b) Circular inside, zero outside
Explanation: The magnetic field in a toroidal solenoid is confined within the core and is circular inside, with zero field outside.



14. A magnetic field exerts a force on a charged particle. For maximum force, the particle must move:

a) Parallel to the field

b) Anti-parallel to the field

c) Perpendicular to the field

d) At an angle of 45°

Answer: c) Perpendicular to the field
Explanation: The force on a charged particle is maximum when it moves perpendicular to the magnetic field (F = qvB sinθ).



15. The direction of the magnetic field in a current-carrying circular loop is:

a) Along the plane of the loop

b) Radially inward

c) Perpendicular to the plane of the loop

d) Radially outward

Answer: c) Perpendicular to the plane of the loop
Explanation: The magnetic field around a current-carrying loop is perpendicular to the plane of the loop.



16. The SI unit of magnetic flux is:

a) Tesla

b) Weber

c) Ampere

d) Henry

Answer: b) Weber
Explanation: The SI unit of magnetic flux is the Weber (Wb).



17. An electron moves with velocity perpendicular to a magnetic field. The path followed by the electron will be:

a) A straight line

b) A circular path

c) A spiral path

d) An elliptical path

Answer: b) A circular path
Explanation: When a charged particle moves perpendicular to a magnetic field, it follows a circular path due to the Lorentz force.



18. The Earth’s magnetic field is due to:

a) Rotation of the Earth

b) Presence of magnetic rocks

c) Currents circulating inside the Earth

d) Gravitational force

Answer: c) Currents circulating inside the Earth
Explanation: The Earth’s magnetic field is believed to be caused by currents of molten iron in its outer core.



19. A current-carrying conductor is placed at an angle of 90° to the magnetic field. The force on the conductor is:

a) Maximum

b) Minimum

c) Zero

d) Equal to its weight

Answer: a) Maximum
Explanation: The force is maximum when the angle between the conductor and the magnetic field is 90° (F = BIL sinθ).



20. Lenz’s law is a consequence of the conservation of:

a) Energy

b) Charge

c) Momentum

d) Mass

Answer: a) Energy
Explanation: Lenz’s law states that the induced emf will oppose the change in magnetic flux, which is a consequence of the conservation of energy.



21. The magnetic field due to a current-carrying wire at a point is inversely proportional to:

a) The current

b) The distance from the wire

c) The length of the wire

d) The strength of the magnetic field

Answer: b) The distance from the wire
Explanation: The magnetic field due to a current-carrying wire decreases with an increase in distance from the wire.



22. In which of the following materials is the magnetic permeability the highest?

a) Air

b) Iron

c) Copper

d) Aluminum

Answer: b)

Answer: b) Iron
Explanation: Magnetic permeability is a property that quantifies a material’s ability to support the formation of a magnetic field. Iron has a very high permeability compared to other materials like air, copper, and aluminum.



23. A rectangular coil carrying current is placed in a uniform magnetic field. The coil will experience maximum torque when:

a) The plane of the coil is perpendicular to the magnetic field

b) The plane of the coil is parallel to the magnetic field

c) The magnetic field is zero

d) The angle between the field and the normal to the coil is 45°

Answer: b) The plane of the coil is parallel to the magnetic field
Explanation: Maximum torque on a current-carrying coil in a magnetic field occurs when the plane of the coil is parallel to the field.



24. What happens to the magnetic field if the number of turns in a solenoid is tripled, while the current remains constant?

a) It becomes one-third

b) It becomes three times as strong

c) It remains unchanged

d) It becomes zero

Answer: b) It becomes three times as strong
Explanation: The magnetic field inside a solenoid is directly proportional to the number of turns, so tripling the number of turns triples the magnetic field strength.



25. A conductor moves through a magnetic field, and an emf is induced across its ends. The magnitude of the induced emf is independent of:

a) The length of the conductor

b) The velocity of the conductor

c) The strength of the magnetic field

d) The resistance of the conductor

Answer: d) The resistance of the conductor
Explanation: The induced emf depends on the length of the conductor, velocity, and the strength of the magnetic field, but not on the resistance of the conductor itself.

26. The magnetic field inside a long straight solenoid -carrying Conductor

a) is zero

b) decreases as we move towards its end

C) increases as we move towards its end.

d) is the same at all points.

Answer: Option(d)

The magnetic field lines inside a solenoid are in the form of parallel straight lines, the reason for this is, the magnetic field inside the solenoid is uniform i.e.option(d).

Explanation:

First, let’s understand some properties of solenoids,

A magnetic field is created when a current is made to flow through a solenoid.
The parallel and even spacing of the magnetic field lines within the solenoid suggests that the magnetic field is of a uniform nature.
Both the density of the current and the number of solenoids turn to affect the magnetic field.
Because the magnetic field inside a solenoid is uniform, the lines that make up its magnetic field are parallel straight lines.
The magnetic field lines inside a solenoid are in the form of parallel straight lines, the reason for this is, that the magnetic field inside the solenoid is uniform i.e.option(d).