A magnet pushes on a current-carrying wire. What force acts on the magnet?

An equal and opposite force acts on the magnet.

How must a wire be placed in a magnetic field for the force on it to be as large as possible?

At right angles to the magnetic field lines.

How big is the force on a current-carrying wire that lies along the magnetic field lines?

There is no force on it at all.

Give two ways of increasing the force on a current-carrying wire in a magnetic field.

Increase the current in the wire, or use a stronger magnetic field.

OCR GCSE Combined Science Physics J250

Electricity

Topic overview Charge, and producing static electricity Transfer of electrons in charging and discharging Current as a rate of flow of charge Charge, current and time Series and parallel circuits, and circuit symbols Current, potential difference and resistance Resistors whose resistance changes, and investigating them Linear and non-linear circuit elements from graphs Net resistance in series and parallel Circuits for measurement, and electrical power

Energy

Topic overview Conservation of energy, and energy stores Energy changes on heating, and calculating them Energy of a moving body, a spring and a raised object Dissipation, and energy transfer in domestic devices Power ratings, efficiency, and increasing it Reducing unwanted energy transfer, and the rate of cooling

Forces

Global Challenges

Topic overview Typical speeds and everyday accelerations Reaction time, stopping distance and the dangers of large decelerations Stopping distance, acceleration and collision force calculations Energy resources, and trends in their use The national grid, and step-up and step-down transformers Why the national grid is efficient, and power in a transformer Mains electricity: a.c., d.c. and the domestic supply Live, neutral and earth wires, and electrical danger

Magnetism and Magnetic Fields

Topic overview Permanent and induced magnets, and magnetic poles Magnetic fields, and the dipping compass The magnetic effect of a current, and solenoids The motor effect and Fleming's left-hand rule The force on a conductor, and how a motor turns

Matter

Topic overview How the atomic model changed, and the structure of the atom The size of atoms, and defining density Density of the states of matter, and density calculations Conservation of mass in changes of state Heating a system, and specific heat capacity Calculations with specific heat capacity and latent heat Gas molecules, temperature and pressure

Radioactivity

Topic overview Protons, neutrons and isotopes Unstable nuclei and the emissions they give out Balancing nuclear equations Electron energy levels, and radiation from atoms Half-life and the randomness of decay Penetration of alpha, beta and gamma Contamination and irradiation, and reducing the hazard

Waves in Matter

Topic overview Amplitude, wavelength, frequency and period The wave equation Transverse and longitudinal waves Modelling waves with ripples and sound Electromagnetic waves as transverse, and energy transfer Frequency and wavelength across the spectrum What our eyes detect, and light as an electromagnetic wave Uses of electromagnetic waves Hazards of ultraviolet, X-rays and gamma rays Producing and receiving radio waves Absorption, transmission, refraction and reflection Investigating reflection and refraction of light

Magnetism and Magnetic Fields

The motor effect and Fleming's left-hand rule

3 things to know
Paper 11 (Physics)

Overview

The force on a current-carrying wire in a magnetic field and the equal force on the magnet, how the angle to the field, the current and the field strength change the force, what reversing the current or field does, and Fleming's left-hand rule with worked directions.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

In Fleming's left-hand rule, what do the first finger, the second finger and the thumb each represent?

Key term

What is the motor effect?

Key term

Explain why a current-carrying wire placed in a magnetic field experiences a force.

Questions from this subtopic

Each one with the model answer underneath.

1
What is the motor effect?
Model answer
The force felt by a current-carrying conductor placed in a magnetic field.
2
Explain why a current-carrying wire placed in a magnetic field experiences a force.
Model answer
The field made by the current interacts with the field of the magnet, and the two fields together push the wire.
3
A magnet pushes on a current-carrying wire. What force acts on the magnet?
Model answer
An equal and opposite force acts on the magnet.
4
How must a wire be placed in a magnetic field for the force on it to be as large as possible?
Model answer
At right angles to the magnetic field lines.
5
How big is the force on a current-carrying wire that lies along the magnetic field lines?
Model answer
There is no force on it at all.
6
Give two ways of increasing the force on a current-carrying wire in a magnetic field.
Model answer
Increase the current in the wire, or use a stronger magnetic field.

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