Question 1

What is the force on a current-carrying conductor in a magnetic field?

Accepted Answer

The force on a current-carrying conductor in a magnetic field is described by the Lorentz force law. It states that a conductor carrying an electric current experiences a force when placed in a magnetic field. This force is perpendicular to both the direction of the current and the magnetic field, and its magnitude is given by the equation F = BIL sin(θ), where F is the force, B is the magnetic flux density, I is the current, L is the length of the conductor, and θ is the angle between the current and the magnetic field.

Question 2

How does the direction of the force on a current-carrying conductor relate to the magnetic field and current direction?

Accepted Answer

The direction of the force on a current-carrying conductor in a magnetic field is determined by the right-hand rule. According to this rule, if you point your thumb in the direction of the current and your fingers in the direction of the magnetic field, your palm will face the direction of the force. This means the force is perpendicular to both the current and the magnetic field, forming a right angle with them.

Question 3

What factors affect the magnitude of the force on a current-carrying conductor?

Accepted Answer

The magnitude of the force on a current-carrying conductor in a magnetic field is affected by several factors: the strength of the magnetic field (B), the amount of current (I) flowing through the conductor, the length of the conductor (L) within the magnetic field, and the angle (θ) between the conductor and the magnetic field. The relationship is given by the formula F = BIL sin(θ), indicating that the force increases with stronger magnetic fields, higher currents, longer conductors, and when the angle approaches 90 degrees.

Question 4

Why is the angle between the conductor and the magnetic field important in determining the force?

Accepted Answer

The angle between the conductor and the magnetic field is crucial because it determines the component of the magnetic field that interacts with the current. The force is maximized when the conductor is perpendicular to the magnetic field (θ = 90°), as sin(90°) = 1. If the conductor is parallel to the magnetic field (θ = 0°), the force is zero because sin(0°) = 0. Thus, the angle affects the effective interaction between the magnetic field and the current.

Question 5

How is the concept of force on a current-carrying conductor applied in real-world devices?

Accepted Answer

The concept of force on a current-carrying conductor is fundamental in the operation of many electrical devices, such as electric motors and loudspeakers. In electric motors, the force on the current-carrying coils within a magnetic field causes rotation, converting electrical energy into mechanical energy. In loudspeakers, the force causes the diaphragm to move, producing sound. Understanding this concept is essential for designing and optimizing such devices, which are integral to modern technology.

Question 6

Why is "Using right hand for current force" a common mistake in Force on a current-carrying conductor ?

Accepted Answer

Why it happens: Confusion with generator rule. How to avoid it: Force on MOTOR (current): LEFT hand. INDUCED current (generator): RIGHT hand. Source: 9702 Examiner Reports 2022-2024

Force on a current-carrying conductor

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Force on Wire Study Notes — Cambridge International A Level Physics 9702 (2025-2027 syllabus)

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Force on current

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1Force on wire (5 marks)

2Direction of force (5 marks)

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Force on current-carrying conductor

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✕Using right hand for current force

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