NEET Physics: Magnetic effects of current and magnetism Practice Questions

Correct answer: B — Magnetic Flux

Magnetic field strength (B) or Magnetic Flux Density is measured in Tesla (T). Magnetic Flux (Φ) is measured in Weber (Wb). Magnetic Field Intensity is often used interchangeably with Magnetic Field strength. Magnetic Inductance (self-inductance) is measured in Henry (H). The unit of magnetic field strength (Tesla) is equivalent to the unit of magnetic flux density, which is related to the magnetic field concept.

Correct answer: B — Perpendicular to the magnetic field line

The magnetic force (Lorentz force on a current element) is proportional to the cross product of the current direction and the magnetic field direction. For a simple straight wire segment, the force is maximum and acts perpendicular to both the current and the magnetic field (if the field is uniform).

Correct answer: B — No force

A magnetic dipole placed in a uniform magnetic field experiences a torque, but no net translational force, as the force depends on the change in magnetic dipole moment (which is zero in a uniform field).

Correct answer: A — Tesla (T)

The SI unit for magnetic field strength (magnetic flux density) is the Tesla (T).

Correct answer: B — F = p × B

The force on a magnetic dipole moment (m⃗) in a magnetic field (B⃗) is given by the cross product F = mB sin θ, which is often represented as F⃗ = ∇ (m⃗ · B⃗) or related forms, but the concept relies on the interaction of magnetic moments. (For conceptual simplicity in an easy setting, focusing on interaction is key).

Correct answer: B — Downwards

The magnetic force is given by F = q(v × B). If the velocity (v) is horizontal and the magnetic field (B) is vertical, the force will be perpendicular to both, resulting in a force directed either left or right, depending on the direction of motion. However, if we consider the standard definition where q is positive (proton), the force is perpendicular to both v and B. Since v is horizontal and B is vertical, the force is horizontal. If the proton moves right, the force is upward (if B is into the page) or downward (if B is out of the page). For a general perpendicular configuration, the force is always perpendicular to both vectors. In this basic setup, the force is perpendicular to both motion and the field direction. Since the specific direction of motion is not given, we rely on the right-hand rule for the force direction: F ∝ vB sin θ. Since the geometry is not specified (e.g., velocity direction), we focus on the directionality relative to the field vector. Assuming the standard setup where motion and B are perpendicular, the force is perpendicular to both.

Correct answer: C — Parallel

Magnetic field lines are always parallel to each other and are always perpendicular to the surface of the magnet or the current-carrying wire.

Correct answer: A — South-West

Using the Right-Hand Rule for magnetic force (F⃗ = I (l⃗ × B⃗)), if the current is North and the field is East, the resulting force direction will be South-West (or vice versa depending on the precise vector interpretation, but the key is the perpendicular relationship). For simplicity and focusing on the conceptual application, the force will be perpendicular to both directions. (Note: A more direct conceptual test might involve force directionality based on the rule).

Correct answer: D — To be perpendicular to both the current and the magnetic field lines

The magnetic force experienced by a current-carrying conductor in a magnetic field is always perpendicular to both the direction of the current and the magnetic field direction (Fleming's Left-Hand Rule).

Correct answer: D — Below the wire

The magnetic field lines from a long straight wire form concentric circles around the wire. The direction is tangential to the circle, which is perpendicular to the wire itself, moving away from it (if we consider the field direction at a point). If the current flows upwards, the field lines circle around it.

Correct answer: C — Repulsive

Parallel currents flowing in the same direction attract each other. If they flow in opposite directions, they repel each other.

Correct answer: C — Tesla (T)

The unit of magnetic field intensity (or magnetic flux density, B) in the SI system is the Tesla (T).

Correct answer: A — BIL

The magnetic force experienced by a current-carrying conductor of length L placed in a uniform magnetic field B is given by the formula F = BIL sin θ. Since the conductor is assumed to be perpendicular to the field for maximum effect (or we consider the magnitude), the basic formula for the force is F = BIL (assuming θ= 90°).

Correct answer: B — Φ= B × A

Magnetic flux (Φ) is defined as the product of the magnetic field strength (B) and the area (A) through which the field is measured, assuming the field is perpendicular to the area (Φ= B A cos θ). If the field is perpendicular (θ=0°), cos 0° = 1, so Φ= B A.

Correct answer: B — The current, the length of the conductor, and the magnetic field strength, and the angle between them.

The magnetic force on a current-carrying wire is given by F = BIL sin θ, where I is current, L is length, B is magnetic field strength, and θ is the angle between B⃗ and L⃗.