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Flashcards in Magnetic Fields Deck (20)
1
Q

Right hand rule

A

Used to determine the direction of a magnetic field around a current-carrying wire

Thumb represents direction of current

Curled fingers represent direction of field

Increasing current

Also used to determine the direction of a magnetic field in a solenoid - fingers represent current, thumb for field direction

2
Q

Fleming’s left hand rule

A

Used to determine direction of force when a current-carrying wire has a flow of current parallel to the direction of the external magnetic field

Thumb - force direction

First finger - direction of uniform magnetic field

Second finger - direction of current

3
Q

Magnetic flux density

A

AKA magnetic field strength - increases with current

The strength of the magnetic field that produces a force of 1 N on 1 metre of wire carrying a current of 1 Amp perpendicular to the magnetic field (Tesla definition)

Measures in teslas, T

1 Tesla = 1 Newton per Amp metre

T=N/Am

4
Q

Moving a charged particle in a circular path

A

F=mv^2/r and F=BQv

r = mv/BQ

Radius of curvature increases (less deflection) with increases in mass or velocity

Radius of curvature decreases (more deflection) with increases in field strength or charge

5
Q

Line of force - magnetic field line

A

A line along which a North Pole would move in the field

6
Q

Motor effect

A

The force on a current-carrying conductor due to a magnetic field

7
Q

Investigating flux density

A

Use a wire connected to a mass on a balance going through a magnetic field perpendicular to the field

Record initial mass and length

Record mass for each value of current

Covert mass to force = mg

Plot a graph of force against current - gradient = Bl

8
Q

Magnetic force on a charged particle

A

Results in a circular orbit - force of the magnetic field is at right angles to the motion

Doesn’t change the speed no work is done

F = BQv F = mv^2/r

r = (mv)/BQ

9
Q

Cyclotron

A

Made of two semicircular electrodes with a uniform magnetic field applied perpendicular to the plane of the electrodes

An alternating potential difference is applied between the electrodes

10
Q

How does a cyclotron work?

A

Charged particles are fired into than electrode the magnetic field makes them follow a semicircular path and leave the electrode

P.d accelerated the particles across the gap into the other electrode

This increases the speed so it’s path has a larger radius

P.d reversed and the process repeated increasing speed and spiralling outwards until it leaves the cyclotron

11
Q

Magnetically hard and soft

A

Hard -> Permanent magnets

Soft -> temporary magnets

12
Q

Magnetic materials

A

Iron
Nickel
Cobalt
Steel

13
Q

Inducing magnetism

A

Magnetism can be induced of a material is placed in a magnetic field

14
Q

Increasing field strength of a solenoid

A

Increase the current

Increase the number of turns in the coil

15
Q

Increasing force on a wire in a magnetic field

A

Increase magnetic field strength - flux density

Increase current

Increase length (e.g. More coils)

16
Q

Mass spectrometer

A

Used to analyse the type of atoms present

The atoms are ionised and directed at a narrow beam into a uniform field

Ions are all at the same velocity - a velocity selector ensures this

Each ion is deflected by a different amount onto the detector - allowing them to be identified

17
Q

Velocity selector (for mass spectrometer)

A

Only allows ions through travelling at a certain velocity, v

Same velocity is important when identifying ions as it impacts radius

v must be such that the force from the electric field is equal to the force from the magnetic field

BQv = EQ

18
Q

Alternating current

A

The charge carriers in a circuit repeatedly reverse their direction if an alternating p.d. is applied

Frequency of a.c. = number of cycles per second

Mains electricity has a frequency of 50Hz

Peak value of p.d. or current is maximum value in either direction

Peak to peak value = 2 X peak value

Peak value of mains = 325 V

Root mean square value of mains = 230V

19
Q

Fleming’s left hand rule for a moving electron

A

Remember current direction is in the OPPOSITE direction to the direction of the electrons motion

Then just use the left hand rule to find the direction of the force

20
Q

When is the magnetic force on a charge when in a magnetic field 0?

A

Charge is stationary

Charge is moving parallel to the field