Magnetic Fields

Question 1

Motor effect

Answer 1

Current makes force

Question 2

Dynamo effect

Answer 2

Force makes current

Question 3

Dynamo effect and motor effect link

Answer 3

Dynano effect tried to stop motor effect

Apply force
1.creates current
2. motor effect
3. This current creates force in opposite direction

Question 4

Lenz Law

Answer 4

The direction of an induced current is such that it would oppose the change that caused it

Question 5

If the top of the solenoid is North Pole what direction does current rotate

Answer 5

Anticlockwise ( N )

Question 6

Mass spectroscopy purpose

Answer 6

Finding the mass of a particle

Question 7

What’s the similarities/ difference of Grwvitation and electrostatic forces

Answer 7

Similar = inverse square law
-use of field lines, use of potential, equipotential surfsced

Mass always attracts, charges may attract or repel

Question 8

Mass spectroscopy

Answer 8

-

Question 9

Cyclotrons

Answer 9

• to increase radius, polarity of electric field switches, accelerating the proton

r = mv / (BQ)

F = BQ/2pim T = 2pir/v

F = frequency of the alternating voltage
Q = charge of the particle (C),
B = magnetic field strength (T),
M = mass of the particle (kg).

Question 10

When flux increases from 0 to 2 linearly,what happens to emf …and back from 2 0

Answer 10

EMF instantly increases to a value = gradient and stays there as flux increases linearly so emf remains constant..
when it’s fully entered the coil, the flux stays the same so emf induced = 0
- when exiting, the flux reduces from 2 to 0 linearly, so the gradient is negative and emf induced is a maximum but in opposite direction and then when the conductor has left the coil emf instantly goes to zero.

Question 11

Back EMF

Answer 11

When motor spins, produces dynamo effect due to lenz law
-supply same V to motor
-opposing emf is high when spinning fast
-unloaded
-opposing emf is small
-heavy load

Question 12

EMF induced entering a coil

Answer 12

-Eo = BANw

E = Eocos(wt)

E = BANwcos(wt)

Question 13

Half wave rectification

Answer 13

-so a normal sin wave but the negative y values are removed so there’s a gap inbetween

Question 14

Full wave rectification

Answer 14

Modulus of a sin graph

Question 15

Power for AC

Answer 15

Vrms x Irms

Question 16

What is permitivity

Answer 16

Permittivity is the measure of how easy it is to generate an electric field in a certain material

Question 17

If the polar molecules align and their opposing electric field increases what happens to permitivity

Answer 17

Increases

Question 18

Why do polar molecules increase capacitance

Answer 18

-oppose electric field produced by the plates
-reduces overall electric field
-decrease potential between the plates
-Capacitance increases

Question 19

What happens during charging

Answer 19

-power supply pushes electrons from positive to negative plate
-does work on the electrons so electrical energy becomes stored on the plates
-as more charge builds up on negative plate. Repulsion increases
-more work needed to push electron so voltage increases

Question 20

What does time constant mean for a charging capacitor

Answer 20

The time taken for the charge or voltage of a charging capacitor to rise to 63% of its maximum value

Question 21

What does time constant mean for a discharging capacitor

Answer 21

The time taken for the charge, current or voltage of a discharging capacitor to decrease to 37% of its original value

Question 22

Why does a conductor cutting field lines Create an EMF

Answer 22

-The upwards motion of the wire as it cuts across the magnetic field lines gives rise to an emf within a wire
E = BLV

Question 23

How can you explain Lenz law when cutting field lines

Answer 23

• so when the electron moves to one side and the other side of the conductor becomes positive. An emf is created
  -However current would flow from the electron to positive side which creates a force downwards.. this means you have to do work to move the wire upwards to oppose the downwards force