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Physics 9702 Theory > Magnetic fields > Flashcards

Magnetic fields Flashcards

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1
Q

Definition

Magnetic field

A

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

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2
Q

Seperation between field lines is an indication of?

A

the field’s strength

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3
Q

Direction of field line at any point shows?

A

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

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4
Q

What are magnetic fields created by?

A

Moving Charges

wire- free electrons
magnet- movement of electrons within atoms

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5
Q

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

A

right hand grip rule

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6
Q

Similarities of electric, gravitational and magnetic fields

2

A
  • decreasing strength with distance from source of the field
  • representation by field lines- direction of which show direction of force
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7
Q

Out of page

A

circle

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8
Q

Into page

A

cross

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9
Q

Force formula

A

BIL sin(θ)

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10
Q

Magnetic force on a moving charged particle formula

A

F=BQv

or Bev

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11
Q

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

A

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

known as motor effect

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12
Q

Magnetic flux density def

A

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

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13
Q

Hall effect

A

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

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14
Q

Hall voltage formula

A

BI/ ntq

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15
Q

Derive hall voltage formula

A
  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

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16
Q

What is the purpose of a hall probe

A

To measure the magnetic flux density

17
Q

How is a hall probe used (3)

A
  • 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
18
Q

How to increase magnetic field due to current in a solenoid

A

Using a ferrous core

19
Q

making reference to transformers

why are the coils wound on a core made of iron

A

To concentrate the magnetic flux

20
Q

making reference to transformers

Why is thermal energy generated in the core

2

A

changing flux increases current
current in core causes a heating effect

21
Q

Magnetic flux definition

A

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

22
Q

Magnetic flux formula

A

BA

23
Q

Magnetic flux linkage definintion

A

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

24
Q

Magnetic flux linkage formula

A

NBA
N= number of turns

25
Q

Faraday’s law

A

Magnetic field of the induced emf is directly proportional to the rate
of change of magnetic flux linkage

E= ΔNΦ/ Δt

26
Q

Lenz’s law

A

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

27
Q

Define the tesla

3 marks

A
  • Newton per ampere
  • Newton per metre
  • Magnetic field normal to current
28
Q

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

A

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

29
Q

Gravitational and electric force mentionned

Similarities between electric force, magnetic force and gravitational force

3

A
  • 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
30
Q

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

A

B

31
Q

Formula to calculate momentum of a particle

A

By equating mv^2/ r and Bev

P=mv
P= Ber

32
Q

Regarding induced emf when a magnetic field cuts the field of a current

for a straight wire, factors affecting induced emf?

3

A
  • magnitude of magnetic flux density, B
  • length of wire in field
  • speed of wire moving across the magnetic field
33
Q

Regarding induced emf when a magnetic field cuts the field of a current

for a coil of wire, induced emf depends on

3

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

Physics 9702 Theory (13 decks)

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