Question 1

What is the motor effect in physics?

Accepted Answer

The motor effect is the force experienced by a current-carrying conductor when placed in a magnetic field. This force is perpendicular to both the current and the magnetic field, and its direction can be found using Fleming's left-hand rule. The effect is used in electric motors to convert electrical energy into kinetic energy.

Question 2

How do you use Fleming's left-hand rule?

Accepted Answer

Hold your left hand with thumb, first finger, and second finger all at right angles. Point your First finger in the direction of the magnetic Field (from north to south). Point your seCond finger in the direction of the Current (from positive to negative). Your thuMb then points in the direction of the force (motion). This rule helps determine the direction of the force on a current-carrying wire in a magnetic field.

Question 3

What is the formula for the force on a current-carrying wire?

Accepted Answer

The formula is F = BIL, where F is the force in newtons, B is the magnetic flux density in teslas, I is the current in amperes, and L is the length of wire in the magnetic field in metres. This formula applies when the wire is perpendicular to the magnetic field. If the wire is at an angle θ, use F = BIL sinθ.

Question 4

How does a simple electric motor work?

Accepted Answer

A simple motor has a coil of wire placed between the poles of a magnet. When current flows through the coil, the motor effect produces a force on each side of the coil, causing it to rotate. A split-ring commutator reverses the direction of the current every half turn, so the coil continues rotating in the same direction. The speed can be increased by using a stronger magnet, increasing the current, or adding more turns to the coil.

Question 5

What is magnetic flux density?

Accepted Answer

Magnetic flux density (B) is a measure of the strength of a magnetic field, measured in teslas (T). It is defined as the force per unit length per unit current on a current-carrying conductor placed perpendicular to the field. A field of 1 T exerts a force of 1 N on a 1 m wire carrying 1 A.

Question 6

Why does a current-carrying wire not always experience a force in a magnetic field?

Accepted Answer

The force on a current-carrying wire depends on the angle between the wire and the magnetic field. If the wire is parallel to the field lines, no force is exerted because the current is not cutting across the field. The force is maximum when the wire is perpendicular to the field. This is because the motor effect relies on the interaction between the magnetic field and the magnetic field created by the current.

Topic 12 – Magnetism and the motor effect

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 13 – Electromagnetic induction

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