Aqa Physics A Level Magnetic Fields

Front 1

What is the difference between a step up and step down transformer?

Back 1

step up: Ns>Np Vs>Vp

step down: Nsp Vsp

Front 2

How does kinetic energy change around a non-circular orbit?

Back 2

When closer, PE is smaller and KE is bigger due to bigger attractions and small radius

When further away PE is greater, the force of attraction is less, so velocity and therefore KE is smaller

Front 3

What is a couple?

Back 3

A coil of wire in a magnetic field, the coil rotates and each side feels an equal but opposite force

Front 4

How do you work out torque on a couple in a magnetic field?

Back 4

Torque is the turning force

Torque = Fwcos_alpha_

Fwcos_alpha_= BILnwcos_alpha_BILnA

Front 5

How do you work out force on a moving charge in a magnetic field?

Back 5

F=BQvsin_theta_ when velocity at angle _theta_ to magnetic field

Front 6

How do you work out the radius of the orbit of a moving charge in a magnetic field?

Back 6

r= mv/BQ

(remember specific charge is Q/m)

Front 7

How do you work out the time period of the orbit of a moving charge in a magnetic field?

Back 7

t=2_pi_m/BQ

(remember specific charge is Q/m)

Front 8

How does a cyclotron work?

Back 8

A cyclotron is 2 semicircle electrodes with a gap. Particles are accelerated across the gap, which makes speed and radius increase. An alternating current is used to make the particles cross the gap. The time period stays the same. Uses include medical imaging and cancer therapy.

Front 9

What is magnetic flux?

Back 9

symbol _phi_

the number of magnetic field lines in an area

phi=BA

units: weber (wb) 1wb=1Tm^2

Area and magnetic flux are perpendicular

Front 10

What is magnetic flux linkage?

Back 10

A measure g the magnetic flux of a coil of wire

N_phi_=BANcos_theta_

Front 11

What is electromagnetic induction?

Back 11

If there is relative motion between a wire and magnetic field, an emf is induced in the wire

Front 12

How does electromagnetic induction work?

Back 12

The electrons in the wire experience a force which causes them to move to one end of the wire. A current is induced if the wire is part of the circuit. No emf is induced if the wire is parallel to the magnetic field

Front 13

How do you increase the end induced in electromagnetic induction?

Back 13

Move the wire or magnetic field faster

Use a stronger magnet

Use a coil of wire and increase the number of turns

Front 14

What is Lenz’s law?

Back 14

The direction of the induced current opposes the change that caused it

Front 15

What is Farraday’s law?

Back 15

The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit

epsilon=-N_deltatheta_/_delta_t

Front 16

What is the difference between AC and DC?

Back 16

AC uses a slip ring commutator- current leaving changes every 180 degrees

DC uses a split ring commutator- the current leaving is always in the same direction

Front 17

What is the peak voltage on an oscillator?

Back 17

Distance between the peak and equilibrium

Front 18

What is the peak voltage on an oscillator?

Back 18

Distance between the peak and equilibrium

Front 19

What is Irms?

Back 19

The current in DC that would give the same hearing effect as AC (same for Vrms)

Front 20

What are transformers?

Back 20

Used in the National Grid, they are used to change pd (peak value of alternating current). Flux is the same as the iron core is the same all the way round.