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Physics > 3. Magnetic Fields and Electromagnetic induction > Flashcards

3. Magnetic Fields and Electromagnetic induction Flashcards

1
Q

B = magnetic flux density
Definition:

A

The strength of the magnetic field

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2
Q

What quantity is B

A

A vector

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3
Q

u⁰ définition

A

The permeability of free space
4(pi) x 10‐⁷

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4
Q

Units of B

A

Teslas (T)

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5
Q

What is needed to use the right hand rule?

A

The distance from the wire is perpendicular

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6
Q

What represents the field INTO the page?

A

Cross

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7
Q

What represents the field OUT of the page?

A

Circle

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8
Q

How can you increase the B of a solenoid?

A

The number of coils
Add an iron core
Increase current

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9
Q

B equation with long straight wire

A

B = u⁰ x I / 2(pi) x a

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10
Q

B equation with a solenoid

A

B = u⁰ x n x I

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11
Q

What does n represent?

A

The number of turns or coils per metre

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12
Q

Force on a current carrying wire

A

F = BIL sinø

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13
Q

What are the conditions for sin ø

A

It is the angle between the magnetic field line

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14
Q

If F = BIL and mv²/r then what can you figure out

A

Centripetal force
Omega
Frequency
Time period

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15
Q

What rule is used for figuring out directions of current

A

Fleming left hand rule

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16
Q

What does the 1st finger represent

A

Magnetic field

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17
Q

What does the 2nd finger represent

A

Current

18
Q

What does the thumb represent

A

Force

19
Q

Force on moving charge equation

A

F = Bqv Sinø

20
Q

What are the three types of particle accelerators

A

Linear accelerator
Cyclotron
Synchrotron

21
Q

What current does a linear accelerator use

A

AC

22
Q

Why do the tubes get longer in a linear accelerator

A

The particle needs to spend the same time period in each tube as the speed increases
The frequency of AC is constant

23
Q

Where is the particle accelerated in a cyclotron or synchrotron

A

In between the gaps and Dees

24
Q

What is the difference between a cyclotron and a synchrotron

A

Synchrotron = circular (2 Dees) = constant radius
Cyclotron = spiral = constant field

25
Q

Why do the protons move in a spiral

A

The electric field accelerates protons across the gaps
The force is towards the centre
As speed increases so does the radius due to mv²/r
The force is centripetal keeping it in circular motion

26
Q

how can the acceleration of a proton increase

A

increase the potential difference

27
Q

what direction do field lines travel in

A

north to south

28
Q

what conditions must there be for f=bvq

A

the magnetic field must be perpendicular to the velocity

29
Q

what are the situations where the magnetic field = 0`

A

when the angle is 0 to moving parallel to the field
when the particle is at rest / velocity = 0

30
Q

if a particle entered a uniform magnetic field and the field then increased what would happen to the path of the particles?

A

they would become more curved and the radius of both particles would decrease

31
Q

What is the hall effect

A

A semiconductor is placed within a magnetic field and a potential difference is created due to the forces on the moving charge carriers

32
Q

how to increase the hall effect

A

use a semi conductor to provide a better voltage
which decreases the uncertainty
also a semiconductor has a smaller n in I=nave so will decrease Vhall

33
Q

Why can devices use the hall effect to measure magnetic fields

A

Vhall is directly proportional to B for a constant current

34
Q

What is the cutting flux

A

when the field lines of a magnetic field are ‘cut’ by a metal

35
Q

what happens when a magnet falls through a metal pipe

A

the magnet slows down and so takes longer to travel through the tube

36
Q

what is lenzs law

A

the direction of any current resulting from an induced emf changes to the oppposite direction to the change in flux linkage

37
Q

what is faradays law

A

the emf induced is proportional to the rate of change in flux linkage
also proportional to the rate of flux cut

38
Q

What equations are used for a velocity selector?

A

F = eq = bvq
Rearrange to solve for a variable

39
Q

how do particles travel in a straight line in a velocity selector

A

the two forces have to be equal to each other

40
Q

Why does increasing the pd between plates increase the velocity

A

E = Bv
E = v / d
bigger pd means bigger electric field and bigger E means bigger velocity

41
Q

How to use a hall probe

A

Place the probe within the magnetic field at right angles

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