7.8 - Magnetic Fields

Question 1

What is a magnetic field?

Answer 1

A region where a force is exerted on magnetic materials.

Question 2

What direction are field lines?

Answer 2

North to south.

Question 3

How do field lines show if a magnetic field is strong or not?

Answer 3

The field lines (or flux lines) will be closer together if the field is stronger.

Question 4

When a current flows through a wire, what is produced around it?

Answer 4

A magnetic field.

Question 5

What do the field lines around a current-carrying conductor look like?

Answer 5

Concentric circles centred on the wire.

Question 6

How do you figure out the direction of a magnetic field around a current carrying wire?

Answer 6

The right-hand rule.
- thumb in direction of current
- way the hand curls around = direction of magnetic field

Question 7

What is a solenoid?

Answer 7

A coil with length (multiple loops in a row).

Question 8

What do the magnetic field lines of a solenoid look like?

Answer 8

Search it up

Question 9

When will a current-carrying conductor experience maximum magnetic force?

Answer 9

When the current through the conductor is perpendicular to the direction of the magnetic field lines.

Question 10

What happens when you put a current carrying wire into the magnetic field of 2 magnets facing each other?

Answer 10

A resultant force upwards is going to be produced. This is because the magnetic fields of both the magnets and the wire are added together, this causes a resultant field.
(can be shown via Fleming’s left hand rule).

Question 11

What is magnetic flux density?

Answer 11

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

Question 12

What is the equation to calculate the force on a current-carrying wire?

Answer 12

F = BILsinθ
F = force on current carrying wire in a B field
B = magnetic flux density of external field
I = current in the wire
L = length of wire
θ = angle between the conductor and external B field

Question 13

Is flux density a scalar or vector?

Answer 13

A vector

Question 14

If the current carrying wire is parallel to the external field, what would the force be?

Answer 14

0, NO FORCE.

Question 15

What represents magnetic field lines coming out the the page?

Answer 15

Dots

Question 16

What represents magnetic field lines going into the the page?

Answer 16

Crosses.

Question 17

What is the derivation of the equation used to find the force on a charged particle?

Answer 17

F = BIL
F = B Q/t x vt
F = BQv

Question 18

In what direction do charged particles move in a magnetic field?

Answer 18

In a circular path.

Question 19

How would you find the radius of a charged particle’s orbit in a magnetic field?

Answer 19

F = mv²/r = BQv
r = mv/BQ

Question 20

What does the circular path of a charged particle in a magnetic field show?

Answer 20

• The radius increases if the mass or velocity of the particle increases
• The radius decreases if the strength of the magnetic field or the charge of the particle increases

Question 21

What are cyclotrons?

Answer 21

A type of particle accelerator that accelerates charged particles from their centre along a spiral path.

Question 22

What are 2 uses of cyclotrons?

Answer 22

• producing medical isotopes (tracers)
• Creating high-energy beams of radiation for radiotherapy.

Question 23

What is the structure of a cyclotron?

Answer 23

• 2 hollow semi-circular electrodes (called dees)
• A Uniform magnetic field applied perpendicular to the electrodes
• An alternating potential difference applied between the electrodes which creates an electric field between them

Question 24

Why is an alternating potential difference used in cyclotrons?

Answer 24

Because the charged particle goes through the gap and is accelerated. It is then on the other semi-circle and the p.d must switch so it is accelerated in the other direction (increasing the path).

Question 25

What is the top-pan balance experiment used for?

Answer 25

To investigate the flux density.

Question 26

How is the top-pan balance experiment manipulated to have to force pushing down onto the top-pan?

Answer 26

The field of the magnets is set and then the current must be facing the direction which makes the force go up. (Fleming’s left hand rule). This is the force on the wire. So as this goes up there is an equal force pushing down on the top-pan (by the magnets).

Question 27

What is the difference in direction of travel for a positive and negative particle in a magnetic field?

Answer 27

If the particle is positive, it moves with the direction of the force (in circular motion)
If the particle is negative, your current finger must point in the opposite direction.