Magnetic fields (C23)

Question 1

What is a B field

Answer 1

A region in which a magnetic material experiences a force

Question 2

Symbol for a magnetic field

Answer 2

B (vector)

Question 3

Which way do field lines point

Answer 3

Direction North pole would move (N–>S)

Question 4

What do equally spaced field lines mean

Answer 4

uniform field strength

Question 5

Why are materials magnetic

Answer 5

Electrons have spin, giving a dipole
This can give regions (domains) a net dipole if the spin aligns
Domains with roughly aligned dipoles give a magnetic material

Question 6

what is a soft magnetic material

Answer 6

Loses dipole after magnet is removed

Question 7

What is a hard magnetic material

Answer 7

Domains remain aligned

Question 8

How do current and magnetic field relate

Answer 8

RH rule

Question 9

What does a wire into the page look like

Answer 9

Cross in circle

Question 10

Wire out of the page

Answer 10

dot in circle

Question 11

What is a solenoid

Answer 11

Coil with multiple turns

Question 12

How do you work poles of a solenoid

Answer 12

Draw with dot and cross wires and look at general field

Question 13

What does a iron core do

Answer 13

Reduces leakage, magnetic fields prefers to go through a magnetic field

Question 14

How do you give solenoid stronger field

Answer 14

More turns
More current
Iron core

Question 15

What is current

Answer 15

the movement of positive charge

Question 16

Why does a current in a magnetic field produce a force

Answer 16

Field from wire and magnetic field interract (lines want to straighten) therefore force

Question 17

How to know direction?

Answer 17

Flemings LH rule

Question 18

Describe Flemmings LH rule

Answer 18

thumb motion
1st field
2nd current

Question 19

Describe the relationship between force and magnetic flux density

Answer 19

Force is proportional to the current, magnetic flux density, and the length of the wire WITHIN the field

Question 20

What is magnetic flux density

Answer 20

Strength of magnetic field

Question 21

Symbol and Unit for magnetic flux density

Answer 21

B [Teslas] or [N/m/A]

Question 22

Experiment to determine magnetic flux density

Answer 22

Scales and wire and magnetic

Question 23

What is a Helmholtz coil

Answer 23

Solenoid pulled apart

~ uniform field in middle

Question 24

if a electron is moving through a magnetic field…

Answer 24

Treat current going the other direction

Question 25

When does F=BQv apply

Answer 25

when particle is moving perpendicular to field

Question 26

Describe movement of charged particle in magnetic field

Answer 26

Force is perpendicular Velocity does not change Direction changes Circular motion

Question 27

What can act as a centripetal force

Answer 27

the force due to the magnetic field on a charged particle

Question 28

Describe a velocity selector is like

Answer 28

Magnetic field and electric field with a charged particle going through it

Question 29

How does a velocity selector work

Answer 29

only particles that are in equilibrium travel straight through BQv=EQ

Question 30

What is v in the velocity selector

Answer 30

E/B ratio of electric to magnetic fields

Question 31

what is a potential difference not

Answer 31

a current

Question 32

How does a spectrometer work

Answer 32

velocity is selected go through a magnetic field radius depends on mass of particle as everything else is constant

Question 33

What is the principle of induction

Answer 33

a magnetic field and force can induce a current

Question 34

Why does induction occur

Answer 34

conservation of energy- electrons in wire experience a magnetic force causing them to move a current to be induced

Question 35

What is magnetic flux

Answer 35

product of magnetic flux density (perpendicular) and the cross sectional area of the coil

Question 36

What is the unit and symbol for magnetic flux

Answer 36

phi | Weber (Wb)

Question 37

SI for Wb

Answer 37

T/m^2

Question 38

What is magnetic flux linkage

Answer 38

N*phi - product of the number of turns in the coil and the magnetic flux of each

Question 39

What is Faraday's Law

Answer 39

Magnitude of EMF produced is directly proportional to the rate of change of flux linkage

Question 40

What is lenz's Law

Answer 40

Direction of EMF induced is always in the direction to oppose the change producing it

Question 41

Is it a n or s pole at the end of solenoid if the magnets n-pole is moving away

Answer 41

South

Question 42

Why is the constant of proportionality in Faraday's Law -1

Answer 42

Lenz's Law

Question 43

Why does Lenz's Law occur

Answer 43

to ensure energy is conserived as work is done to move magnet

Question 44

What does EMF look like on graph

Answer 44

Sinusoidal

Question 45

Why is there alternating current from induction

Answer 45

As flux linkage = BAN cos(theta) | angle changes as inserted

Question 46

Describe a Transformers

Answer 46

two coils of wire around a soft iron core

Question 47

Why do transformers work

Answer 47

AC produces varying magnetic flux | this induces an EMF which induces a current in the wire

Question 48

Turns on a step up transformer

Answer 48

More turns on secondary

Question 49

Describe a step up transformer

Answer 49

raises voltage

Question 50

turns on a step down transformer

Answer 50

more turns on primary

Question 51

What do you remember about ideal transformers

Answer 51

Power is conserved - VI = VI

Question 52

To improve transformers

Answer 52

laminated soft iron core (reduces eddy currents) | low resistance reduces energy as heat lost