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Physics Unit 4 > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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1
Q

What is a Magnetic field (b-field)?

A

A field that exerts a force on magnetised materials

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2
Q

What is the direction of magnetic field lines?

A

They go from the North pole to the South pole

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3
Q

What is the rule used to identify the magnetic field direction around a current carrying wire?

A

Right hand grip rule:

Where Thumb is direction of conventional current
Fingers is direction of magnetic field

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4
Q

What is the magnetic field around a solenoid?

A

Magnetic Field lines will go from the north pole face to the south pole face around the solenoid.
Within the solenoid it is assumed to be uniform and goes south pole to north pole.

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5
Q

How do you increase the magnetic field strength in a solenoid?

A
  1. Increase Current
  2. Increase the number of turns per unit metre
  3. Inserting a magnetic material such as iron into the middle of the solenoid
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6
Q

What happens to a current carrying wire when it is placed within a magnetic field?

A

A force is exerted onto the current carrying wire.

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7
Q

What is the rule used to identify the direction of the force acting on the current carrying wire? and what else does it show?

A

Fleming’s Left Hand Rule:

F - Force direction Thumb
B - B-field index finger
I - Current direction middle finger

Force is always perpendicular to the direction of the B-field and the direction of the conventional current

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8
Q

How do you calculate the force acting on a current carrying wire?

A

F = BILsinθ

B = Magnetic Flux Density
I = Current
L = Length of wire
θ = The angle between the wire and the b-field

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9
Q

What happens to a charged particle that is injected into a magnetic field?

A

A charged particle will follow a circular path when inside a magnetic field due to a centripetal force acting onto the charged particle. This is true only if the charged particle is injected perpendicularly.
If the charged particle is injected at an angle θ then it will travel in a helical path.

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10
Q

How do you calculate the magnetic field strength of a current carrying wire?

A

B = μ₀I/2πx

Where:
μ₀ = permeability of free space
I = Current
x = radial distance from the wire

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11
Q

How do you calculate the magnetic field strength of a current carrying solenoid?

A

B = μ₀nI

Where:
μ₀ = permeability of free space
I = Current
n = number of coils

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12
Q

How does the force act around 2 current carrying wires?

A

When the current is travelling in the same directions the wires attract.
When the current is travelling in opposite directions the wires repel.

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13
Q

How do you derive the equation for the force acting on the charged particle?

A

F = BILsinθ

I = q/t
L = vt

q/t . vt = qv

F = Bqv.sinθ

θ = 0 when injected perpendicular

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14
Q

As charged particles in a magnetic field, follow a circular path, how can you find the radius of the circle motion taken by the particle?

A

F = Bqv = mv^2/r (circular motion)

Bqv = mv^2/r

Bqr = mv

r = mv/Bq

Where:
m = mass
v = velocity
B = Magnetic Flux Density
q = charge of the particle

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15
Q

What is the hall voltage?

A

The hall voltage is the voltage that develops when a magnetic field is applied perpendicularly to a current carrying conductor.

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16
Q

How can you derive the equation for Hall Voltage?

A

Electric Field Strength is given with the equation:

E = V/d

Where d is the width of the conductor.

The electric field will produce a force onto the electrons which is given by:

F=Eq

F = Vq/d

Once the magnetic and electric fields are equal movement of electrons will stop giving us the equation:

Bqv = Vq/d
Bv = V/d

To remove velocity we can use
I = nAve

B(I/nAe) = V/d

V = B.(Id/nAe)

17
Q

How does a Linear Accelerator work?

A

The ions are accelerated in a straight line by an alternating p.d.

The acceleration occurs in the gaps between the drift tubes.

The drift tubes must increase in length as the speed of the ions increases

18
Q

What are the different types of particle accelerators?

A

Linear Accelerators
Cyclotrons
Synchrotrons

19
Q

How does a Cyclotron work?

A

In a cyclotron a uniform magnetic field provides a centripetal force.

An electric field accelerates the charged particle as they cross between the Ds.

The resulting motion is a spiral.

20
Q

How does a Synchrotron work?

A

The synchrotron accelerates ions by passing them through an alternating p.d, this alternating p.d can become increased overcoming the increase in relativistic mass of the particle as it increase due to its increase in speed. The ion is kept in circular motion due to the magnetic field which increases as the speed of the protons increases

21
Q

What does an Iron Core do within a solenoid?

A

Increase the strength of the magnetic field

Physics Unit 4 (7 decks)

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