6.3 - Particles - Electromagnetism

Question 1

What is a magnetic field

Answer 1

A region of space in which moving charged particles are subject to a magnetic force

Question 2

What is a magnetic field line

Answer 2

The path which a north pole would take when placed in a magnetic field

Field lines go from north to south

Question 3

How can you map field lines around a magnet

Answer 3

Use iron filings on paper then put the magnet on the paper

or

use a compass and plot the direction when placed in different places around the magnet then connect them in the direction that the arrow faced

Question 4

How do you represent the strength of a magnetic field on a diagram

Answer 4

How close together the lines are

Question 5

What unit is magnetic flux density

Answer 5

Telsa

Question 6

What does the right hand thumb rule do

Answer 6

Work out the shape of the field around a current carrying wire

Question 7

How do you work out the shape of a field around a solenoid

Answer 7

Where the current is going anticlockwise around the coil is the north pole

Question 8

What is Fleming’s left hand rule

Answer 8

First finger = Field
seCond = Current
thuMb = motion

Thumb
I
I________ First
\
\ Second

Question 9

What is the formula relating magnetic force and the angle between the field and the conductor

Answer 9

F = BILsinθ

B = Magnetic flux density

Question 10

How do you measure flux density (experiment)

Answer 10

Put a current carrying wire in place and then through magnets on either side on top of a top pan balance the force downwards is the weight which can then be found with the length of the wire between the magnets then plot a graph of current against mass
Gradient = BL/g
L and g can be found so B can be calculated

Question 11

What is the equation for magnetic force on a moving charge

Answer 11

F = BQv

Question 12

What is the unit for magnetic flux (Φ)

Answer 12

Weber (Wb)

Question 13

What is the formula for Magnetic Flux

Answer 13

Φ = BAcosθ

Question 14

What is magnetic flux linkage equation

Answer 14

NΦ = BANcosθ

N = number of coils

Question 15

State Lenz’s law

Answer 15

Induced emf is always in a direction so as to oppose the change that caused it

Question 16

State Faraday’s Law

Answer 16

The induced emf in a circuit is proportional to the rate of change of flux linkage throughout the circuit

Question 17

What is the formula that links Lenz’s and Faraday’s law

Answer 17

ε = - (ΔNΦ) / Δt

ΔNΦ = change of flux linkage
ε = induced emf

Question 18

How does a simple AC generator work

Answer 18

The flux linkage in the coil changes continuously inducing an alternating current in the coil

Question 19

How can the peak emf of an ac generator be increased

Answer 19

Increase speed of rotation and increase cross sectional are of the coil

Question 20

How does a transformer work

Answer 20

An ac is run through the primary coil which induces an alternating magnetic field in the iron core this induces an alternating emf in the secondary coil

Question 21

What formula relates the number of turns with the potential difference of each coil

Answer 21

Vs / Vp = Ns / Np

s = secondary coil
p = primary coil

Question 22

What are the conditions for an ideal transformer

Answer 22

100% efficiency , no energy loss

Question 23

How is efficiency calculated for a transformer

Answer 23

Efficiency = Power out / Power in x 100%

Question 24

Define magnetic flux density

Answer 24

The strength of a magnetic field

Question 25

What is the equation for the force on a charged particle in a magnetic field

Answer 25

F = BQvsinθ

Question 26

What is the purpose of a step up and down transformer

Answer 26

Step up increases voltage (reduces current) for transmission
Step down reduce voltage for safe domestic use