Magnetism and Electromagnetism

Question 1

What do magnets produce

Answer 1

Magnetic fields

Question 2

Magnetic field

Answer 2

Region around magnet where other magnets or magnetic material experience a non-contact force of magnetism

Question 3

Direction of magnetic force

Answer 3

North to South

Question 4

Magnetic materials

Answer 4

• iron
• steel
• nickel
• cobalt

Question 5

What do magnetic field lines show

Answer 5

Which way a force would act on a north pole if it was put at that point in the field

Question 6

What do closer magnetic field lines show

Answer 6

Stronger magnetic field

Question 7

What determines strength of magnetic field

Answer 7

Distance from magnet

Question 8

Where is magnetic field strongest

Answer 8

At poles of magnet

Question 9

What is force between magnet and magnetic material always

Answer 9

Attractive

Question 10

How do compasses work

Answer 10

• contain tiny bar magnet inside
• north pole of magnet attracted to south pole of any nearby magnet
• compass needle points in direction of magnetic field

Question 11

How to use compass to trace magnetic field

Answer 11

• move compass around magnet
• trace position of arrow on paper

Question 12

Where/why do compasses point when not near a magnet

Answer 12

• (geographic) North
• needle aligns itself with Earth’s magnetic field

Question 13

What gives Earth its magnetic field

Answer 13

Magnetic core

Question 14

What provides evidence for Earth’s magnetic core

Answer 14

Behaviour of magnetic compass

Question 15

Types of magnet

Answer 15

• permanent
• induced

Question 16

Permanent magnet

Answer 16

• produce own magnetic field, can’t be turned on/off
• can attract or repel

Question 17

Induced magnets

Answer 17

• only produce force of attraction when in magnetic field of another magnet
• when magnetic field removed, loses most/all magnetism quickly
• can only produce force of attraction

Question 18

What creates magnetic field around wire

Answer 18

Current flowing through wire

Question 19

What makes up magnetic field around wire

Answer 19

Concentric circles perpendicular to wire, with wire in centre

Question 20

Effect of changing direction of current

Answer 20

Changes direction of magnetic field

Question 21

Right-hand thumb rule

Answer 21

• thumb points direction of current
• fingers curl direction of magnetic field

Question 22

What affects magnetic field strength around wire

Answer 22

• current size
• distance from wire
• solenoid

Question 23

How does current size affect magnetic field strength

Answer 23

Larger current = stronger

Question 24

How does distance from wire affect magnetic field strength

Answer 24

Closer to wire = stronger

Question 25

Solenoid

Answer 25

Coil of wire

Question 26

How does solenoid affect magnetic field strength

Answer 26

Wrapping wire to form solenoid = stronger

Question 27

Why does solenoid increase magnetic field strength

Answer 27

- field lines around each loop line up with each other - results in lots of field lines pointing in same direction, close together

Question 28

How to increase field strength of solenoid

Answer 28

- turn it into an electromagnet - put block of iron into centre of coil, iron core becomes and induced magnet

Question 29

Electromagnet

Answer 29

Solenoid with an iron core, has magnetic field that can be turned on/off with electric current

Question 30

Motor effect

Answer 30

- current-carrying wire placed between magnetic poles - magnetic field around wire interacts with magnetic field it is placed in - causes magnet and conductor to exert force on each other - causes wire to move

Question 31

How do angles affect force experienced in motor effect

Answer 31

- wire at 90° to magnetic field - experiences full force - wire parallel - experiences no force - wire at angle between - experiences some force

Question 32

What angle does force act at in motor effect

Answer 32

- right angle to magnetic field of magnets - right angle to direction of current in wire

Question 33

How does magnetic field strength affect magnitude of force

Answer 33

As field strength increases, magnitude of force increases

Question 34

How does amount of current passing through conductor affect force

Answer 34

As amount of current increases, force increases

Question 35

What affects force acting on conductor in magnetic field

Answer 35

- magnetic flux density - size of current of conductor - length of conductor in magnetic field

Question 36

Magnetic flux density

Answer 36

How many field (flux) lines there are in a region, showing strength of magnetic field

Question 37

When can FBIL equation be used to find force

Answer 37

When current is at 90° to magnetic field it’s in

Question 38

Unit of magnetic flux density

Answer 38

Tesla (T)

Question 39

Fleming's left hand rule

Answer 39

- thumb and 2 fingers perpendicular to each other - thumb shows direction of force - index finger shows direction of magnetic field - middle finger shows direction of current

Question 40

How does electric motor work

Answer 40

- current flows in opposite directions on each side - magnetic field always acts in same direction (N-S) - causes forces acting up and down - causes coil to spin

Question 41

Split-ring commutator

Answer 41

- swaps contacts every half turn - causes current to reverse every half turn - so motor keeps spinning in same direction

Question 42

How to reverse direction of motor

Answer 42

- swapping polarity of dc supply - reverses current - swapping magnetic poles - reverses field

Question 43

How to increase speed of electric motor

Answer 43

- increase current - add more turns to coil - increase magnetic flux density