What shape are the magnetic field lines around a long straight current-carrying wire?

They are circles centred on the wire.

In which plane do the field lines around a straight current-carrying wire lie?

In a plane at right angles to the wire.

How is the direction of the magnetic field around a straight wire worked out?

By the right-hand grip rule: point the right thumb along the conventional current and the curled fingers give the direction the field circles the wire.

How could iron filings be used to show the field around a vertical current-carrying wire?

Pass the wire through a hole in a horizontal card, sprinkle filings on the card and tap it, and they settle into circles around the wire.

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, and calculating efficiency Reducing unwanted energy transfer, and the rate of cooling

Forces

Topic overview Measuring distance and time, and calculating speed Converting units, and rates Vectors and scalars in motion Distance-time and velocity-time graphs Average speed, and the equations of uniform motion How objects interact, and forces as vectors Newton's first law Newton's second law Work done, and stored energy Power, and Newton's third law Stretching, bending and compressing; elastic and plastic Force and extension, linear and non-linear The spring constant, and work done in stretching Gravitational fields, weight and free fall Calculations with weight and gravitational field strength

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

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 Investigating reflection and refraction of light

Magnetism and Magnetic Fields

The magnetic effect of a current, and solenoids

3 things to know
Paper 5 (Physics)

Overview

Showing that a current has a magnetic effect, the circular field around a straight wire and the right-hand grip rule, how current and distance change the field strength, the field inside and outside a solenoid, ways of making a solenoid stronger, and electromagnets.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Evaluation

What is a solenoid, why is the field stronger than a single wire's, how is the field strengthened, and why does an iron core help?

Key term

Describe a simple demonstration showing that an electric current produces a magnetic effect.

Key term

What happens to the direction of the magnetic field if the current in a wire is reversed?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe a simple demonstration showing that an electric current produces a magnetic effect.
Model answer
Place a plotting compass beside a straight wire, and the needle is deflected as soon as the current is switched on.
2
What shape are the magnetic field lines around a long straight current-carrying wire?
Model answer
They are circles centred on the wire.
3
In which plane do the field lines around a straight current-carrying wire lie?
Model answer
In a plane at right angles to the wire.
4
How is the direction of the magnetic field around a straight wire worked out?
Model answer
By the right-hand grip rule: point the right thumb along the conventional current and the curled fingers give the direction the field circles the wire.
5
What happens to the direction of the magnetic field if the current in a wire is reversed?
Model answer
The field circles the wire the opposite way round.
6
How could iron filings be used to show the field around a vertical current-carrying wire?
Model answer
Pass the wire through a hole in a horizontal card, sprinkle filings on the card and tap it, and they settle into circles around the wire.

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Electricity

Energy

Forces

Global Challenges

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