Electromagnetism - Magnets

Question 1

Magnets

Answer 1

Magents are always dipolar, always drawn from north to south

Question 2

Direction of magnetic field

Answer 2

x - current flowing into the page
. - current flowing out of the page

Question 3

Strength of magnetic field

Answer 3

B = μI/2pir

Question 4

Solenoids Magnetic Field Strength

Answer 4

B = μnL

Question 5

Right hand thumb rule - current carrying wire with magnetic field

Answer 5

Thumb pointing in direction of current
Finger pointing in direction of magnetic field

Question 6

Right hand grip rule - solenoids

Answer 6

Finger curl in the direction of the current
Thumb points in the direction of B field (North)

Question 7

Magnetic Force Parallel Wires

Answer 7

Parallel - The wires are futher way so weak fields between wires forces them inwards
Series - The wires are closer so strong fields between wires forces them outwards

Question 8

Magnetic Force - Current carrying wire in B field

Answer 8

When a current carrying wire is put in a external B field. The south side of the wire attaches to the north side of the B field and vica versa

Question 9

Right hand rule - magnetic force of current carrying wire in B field

Answer 9

Thumb points in the direction of positive charge
Palm points in the direction of the force
Fingers point in the direction of the field

Question 10

Equation of magnetic force of current carying wire

Answer 10

F = BILsintheta
where F is the force (N)
I is the current through the wire (A)
L is the length of the wire in the B field (m)
sintheta - the angle of the wire in the B field

Question 11

Magnetic force on a single charge

Answer 11

Derived from F = BIL and I = q/t
F = qvb
F = qvbsintheta

Question 12

Rigth hand palm rule - magnetic force on a single charge

Answer 12

Thumb is direction of positive charge (opposite if charge in negative)
Palm is direction of force F
Fingers are the direction of the B field

Question 13

Negative charged particle in a magnetic field

Answer 13

Follows a circular path where v = square root of 2qV/m
1/2mv2 = qv

Question 14

Magnetic Flux

Answer 14

The amount of magnetic field (scalar) that flows through a particular area

Φ = BAcostheta
costheta is the angel from the normal of the field

Question 15

Faradays Experiment

Answer 15

Oersted said a current should induce a B field
Faradays expected the magnetic field to induce a current, but instead proved only a changing flux induces a current known as electromagnetic induction
A change in flux produces an induced electromotive force (EMF) and hence an induced current

Question 16

Induced EMF equation

Answer 16

E = IvB
emf = -n x change in flux/change in time

Question 17

Faradays Law

Answer 17

When magnetic flux linking a circuit changes, an EMF is induced proportional to the rate of change of the flux linkage

Question 18

Lenz’s Law

Answer 18

The direction of an induced current is such that it will always oppose the change in flux that created it, so induced magnetic field will be opposite to existing one. Use right hand grip rule to find current

Question 19

Transformers

Answer 19

Use an alternating current supply to constantly change magnetic flux and induced an EMF in a secondary nearby coil

Question 20

Alternating current

Answer 20

where electrons flow from both directions, alternating every 50th second

Question 21

Transformers Equations

Answer 21

V(primary)/ V(secondary) = n(primary)/n(secondary
I(secondary)/I(primary) = n(primary)/n(secondary)
Step down tranformer when Vp is larger than Vs
Step up transformer when Vs is larger than Vp

Vp = magnetic flux

Question 22

What angle does a current have to be from the magnetic field to produce the greatest strength?

Answer 22

90 degrees or 270 (perpendicular)
180 and 0 provide the least (parallel)