Physics Aqa - Unit 4 - Magnetic Fields

Front 1

Magnetic Fields can be formed around?

Back 1

A magnetic field is formed around a current carrying wire. (Use Right Hand Grip Rule)

Front 2

What do you use Fleming's Left Hand Rule for?

Back 2

A current carrying wire experiences a force in a magnetic field. Use Fleming’s Left Hand Rule.The magnitude of the force is : F = B I l

Front 3

What does a moving charge in a magnetic field feel? And what is this the same as?

Back 3

A charge moving in a magnetic field experiences a force. A moving charge is the same as a current. Use Fleming’s Left Hand Rule. The magnitude of the force is given by: F = B q v

Front 4

What do cyclotrons use magnetic fields for?

Back 4

Cyclotrons use magnetic fields to keep charged particles in circular orbits

Front 5

When a wire moves in a magnetic field what happens?

Back 5

A current is induced in a wire if it moves in a magnetic field. (Use Fleming’s Right Hand Rule)

Front 6

What is Faraday's law?

Back 6

The induced e.m.f. is directly proportional to the rate of change of magneticflux linkage

Front 7

What is Lenz's law?

Back 7

The direction of the induced e.m.f. is such as to oppose the change that inducesit

Front 8

What do step-up transformers do?

Back 8

Step-up transformers increase the voltage

Front 9

Why is a high voltage used in the national grid?

Back 9

High voltage is used in the National Grid to reduce power loss to resistance of cables

Front 10

What causes inefficiency?

Back 10

Causes of inefficiency:o Eddy currentso Resistance in coilso Not all of magnetic flux though coil one passes through coil two

Front 11

What can magnetic fields be represented by?

Back 11

Magnetic fields can be represented by field lines, field lines go from north to south and the closer together the lines, the stronger the field

Front 12

What is the difference in field lines of looping into a coil or solenoid (lots of coils)?

Back 12

If you loop a wire into a coil, the field line is doughnut shaped.
If you have lots of coils, it forms a field like a bar magnet

Front 13

What happens if you put a current-carrying wire into an external magnetic field?

Back 13

If you put a current carrying wire into an external magnetic field, the field around the wire and the magnetic field interact. The magnetic field lines contract to form a 'stretched catapult' effect, where the flux lines are closer together

Front 14

What is magnetic field strength defined as for a current-carrying wire in a magnetic field?

Back 14

The force on one metre of wire carrying a current of one amp at right angles to the magnetic field

Front 15

What is magnetic field strength/flux density measured in?

Back 15

Magnetic field strength/flux density is measured in Tesla's (T)

Front 16

What path do charged particles in a magnetic field follow?

Back 16

Charged particles in a magnetic field follow a circular path - you can identify different particles by how they are deflected as you can gain information on their charge and mass (due to the path they take)

Front 17

What is magnetic flux density?

Back 17

Magnetic flux density a measure of strength of a magnetic field per unit area

Front 18

How does a conducting rod induce an EMF in a magnetic field?

Back 18

When moving through the magnetic field, the electrons within it will experience a force, meaning they will accumulate at one side of the rod. This will induce an EMF across the ends of the rod, if attached to a circuit this can be used to induce a current - electromagnetic induction

Front 19

Flux cutting always induces an ____ but will only induce a ____ if the circuit is complete?

Back 19

Flux cutting always induces an EMF but will only induce a CURRENT if the circuit is complete

Front 20

What is flux linking?

Back 20

Flux linking is when an EMF is induced by changing the magnitude or direction of the magnetic flux

Front 21

What does the area under a graph of EMF against time give?

Back 21

The area under the graph of EMF against time gives the flux change