# 6.3 Electromagnatism Flashcards

1
Q

Magnetic Field

A

A region where a force will act on a magnetic or charged material

2
Q

What the closeness of field lines represents

A

The magnetic flux density

3
Q

Direction of a magnetic field around a wire

A

Use right hand rule

4
Q

A circle with a dot vs cross

A

dot - out of plane

cross - into plane

5
Q

Solenoid

A

A long coil of current carrying wire

6
Q

What causes a magnetic field

A

Moving charges or permanent magnets

7
Q

When a force is induced by a magnetic field

A

When a current is perpendicular to a uniform field

8
Q

Flemings left hand rule

A

First finger - field
seCond finger - current
thuMb - motion

9
Q

Causes of a magnetic field (2)

A
• Moving charges

- Permanent magnets

10
Q

Force on a current carrying conductor

A

F = BILsinθ

11
Q

Experiment to determine magnetic flux density

A

Set up a wire between two permanent magnets and place the setup on some digital scales. Set the scales to 0. The circuit should contain a variable resistor and ammeter. Turn on the circuit and a downwards force will be produced causing a reading on the scales, note this down along with the current. Vary the resistance and repeat this. Plot a graph of F(=mg) against I and the gradient will be Bl so divide by l (length of magnets) to obtain the flux density

12
Q

Force on a charged particle in a magnetic field

A

F = BQv

13
Q

Motion of charged particles inside a uniform magnetic field

A

They will move in a circular path

14
Q

How to calculate the radius of the circular path of a charged particle in a magnetic field

A

Equate centripetal force to the force from the magnetic field

15
Q

How velocity selectors work

A

There is a magnetic field acting in an opposite direction to an electric field and charged particles are projected perpendicular to the direction of the fields. There is a small gap directly ahead and therefore to make it through the gap the force of the magnetic field must equal the force of the electric field.
EQ = BQv
E = Bv
v = E/B
Therefore only particles with a velocity of E/B will make it through

16
Q

Magnetic flux

A

Magnetic flux density * perpendicular area

17
Q

A

Magnetic flux * number of coils

18
Q

A

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

19
Q

A

negative e.m.f.

20
Q

Area under a e.m.f. - time graph

A

21
Q

Lenz’s law

A

Induced e.m.f. will be in a direction to oppose the change that caused it

22
Q

So whats the big idea with why you can move straight wires in a field and get emf but when you move a coil you dont

A

Perhaps because its round so the emf would go both ways and cancel itself out who knows

23
Q

A

Place a search coil between two magnets. The search coil should be connected to a data recorder which will record the induced e.m.f. with a very small time interval. Move the coil out of the field and look at the graph. The area under the e.m.f-time graph should be equal to the magnetic flux linkage. So you can then find B from this (youll need to measure area and number of coils e.t.c.)

24
Q

Components of an A.C. generator (4)

A
• Magnets
• Coil
• Slip rings
• Brushes
25
Q

How an A.C. generator works

A

A coil is forced to rotate inside a magnetic field. The relative change in flux linkage induces an e.m.f.

26
Q

How transformers work

A

The alternating current in the primary coil causes the magnetic field in the iron core to change. This change in the magnetic field induces an e.m.f. in the secondary coil.

27
Q

Experiment to investigate transformer

A

Set up a transformer with a voltmeter on both coils. Run a current through the primary coil and record both voltages, repeat for different currents. n1/n2 should equal v1/v2