Magnetic fields

Question 1

Definition

Magnetic field

Answer 1

Region of space where a force is experienced by a moving charge

Question 2

Seperation between field lines is an indication of?

Answer 2

the field’s strength

Question 3

Direction of field line at any point shows?

Answer 3

direction of force that a ‘free’ magnetic north pole would experience at thtat point

Question 4

What are magnetic fields created by?

Answer 4

Moving Charges

wire- free electrons
magnet- movement of electrons within atoms

Question 5

Direction of field lines in coil/ wire can be found using

Answer 5

right hand grip rule

Question 6

Similarities of electric, gravitational and magnetic fields

2

Answer 6

• decreasing strength with distance from source of the field
• representation by field lines- direction of which show direction of force

Question 7

Out of page

Answer 7

circle

Question 8

Into page

Answer 8

cross

Question 9

Force formula

Answer 9

BIL sin(θ)

Question 10

Magnetic force on a moving charged particle formula

Answer 10

F=BQv

or Bev

Question 11

Explain the origin of magnetic force on current carrying conductor when in magnet`

Answer 11

the combined fields of the current carrying conductor and the fields of the magnet interact, creating a magnetic force

known as motor effect

Question 12

Magnetic flux density def

Answer 12

force acting per unit current per unit length on a wire placed at right angles to a magnetic field

Question 13

Hall effect

Answer 13

the production of p.d across an electrical conductor when an external magnetic field is connected perpendicular to the direction of current

Question 14

Hall voltage formula

Answer 14

BI/ ntq

Question 15

Derive hall voltage formula

Answer 15

1. Equate the two formulas
   F=Bev
   F=Ee, E= V/d. to get Bev= hall Ve/d
2. Substitute I= nave , v= I/nae
3. Substitute A=dt

final formula:
hall V= BI/ ntq

Question 16

What is the purpose of a hall probe

Answer 16

To measure the magnetic flux density

Question 17

How is a hall probe used (3)

Answer 17

• place flat surface of probe between the magnet
• ensure that the surface is perpendicular to the magnetic field (or else reading will be reduced)
• value on connected voltmeter will show hall voltage

Question 18

How to increase magnetic field due to current in a solenoid

Answer 18

Using a ferrous core

Question 19

making reference to transformers

why are the coils wound on a core made of iron

Answer 19

To concentrate the magnetic flux

Question 20

making reference to transformers

Why is thermal energy generated in the core

2

Answer 20

changing flux increases current
current in core causes a heating effect

Question 21

Magnetic flux definition

Answer 21

Magnetic flux is the product of magnetic flux density and the cross sectional area
where area is perpendicular to the magnetic field

Question 22

Magnetic flux formula

Answer 22

BA

Question 23

Magnetic flux linkage definintion

Answer 23

(magnetic) flux density × area × number of turns M1
area is perpendicular to (magnetic) field A1

Question 24

Magnetic flux linkage formula

Answer 24

NBA
N= number of turns

Question 25

Faraday's law

Answer 25

Magnetic field of the induced emf is directly proportional to the rate of change of magnetic flux linkage | E= ΔNΦ/ Δt

Question 26

Lenz's law

Answer 26

induced emf is in the direction so as to produce effects that oppose the change producing it | E= - ΔNΦ/ Δt the minus sign shows the law

Question 27

Define the tesla | 3 marks

Answer 27

- Newton per ampere - Newton per metre - Magnetic field normal to current

Question 28

Why do electrons follow a circular path when inside the region of the magnetic field 3

Answer 28

Force is always perpendicular to velocity Magnetic force provides centripetal force Magnitude of force is constant

Question 29

# Gravitational and electric force mentionned Similarities between electric force, magnetic force and gravitational force | 3

Answer 29

- all defined in terms of a force on a unit mass, charge or current - decreaseing strenght with distance from the source of the field - represented by field lines whose direction show the direction of force

Question 30

The magnetic force acting on a moving charge through a magnetic field is either: A in direction of velocity B perpendicular to direction of velocity

Answer 30

B

Question 31

Formula to calculate momentum of a particle

Answer 31

By equating mv^2/ r and Bev P=mv P= Ber

Question 32

# Regarding induced emf when a magnetic field cuts the field of a current for a straight wire, factors affecting induced emf? | 3

Answer 32

- magnitude of magnetic flux density, B - length of wire in field - speed of wire moving across the magnetic field

Question 33

# Regarding induced emf when a magnetic field cuts the field of a current for a coil of wire, induced emf depends on | 3

Answer 33

- magnetic flux density, B - number of turns of wire - cross-sectional area of coil