Magnetism And Electromagnetism

Question 1

How many poles do magnetic have

Answer 1

• 2
• north (north seeking) and south (south seeking

Question 2

What is a magnetic field

Answer 2

• a region where other magnets or other magnetic materials experience non contact forces

Question 3

How to show magnetic field

Answer 3

• drawing magnetic field lines

Question 4

What do magnetic field lines show

Answer 4

• the closer the lines are, the stronger the magnetic field and vice versa

Question 5

Where is the strongest point in a magnetic field

Answer 5

• strongest at the poles
• this mean the magnetic forces are also strongest at the poles

Question 6

4 main magnetic metals

Answer 6

Iron
Steel
Nickel
Cobalt

Question 7

What happens when 2 poles of a magnet are put near each other

Answer 7

• they will each exert a force on each other
• this force can be attractive or repulsive

Question 8

Are magnetic materials an magnets always attracted to eachother

Answer 8

Yes, the forces are always attractive no matter the pole

Question 9

What happens when a compass is next to a bar magnet

Answer 9

• inside the compass is a tiny bar magnet
• the North Pole of the compass magnet points along the field line towards the South Pole of the bar magnet

Question 10

Where do compasses point when they’re NOT near a magnet

Answer 10

• they always point to magnetic north
• this is because the earth generates its own magnetic field, which shows the inside of earth must be magnetic

Question 11

What is a permanent magnet

Answer 11

• magnets that produce their own magnetic field

Question 12

What is an induced magnet

Answer 12

• magnetic materials that turn into a magnet when they’re put into a magnetic field
• when you take away the magnetic field, induced magnets quickly lose their magnetism and stop producing a magnetic field

Question 13

What is the force between permanent and induced magnets like

Answer 13

They’re always attracted to each other

Question 14

What happens when current flows through a wire

Answer 14

• a magnetic field is created around the wire
• the field is made up of concentric circles perpendicular to the wire, with the wire in the centre

Question 15

How to you see magnetic field around a wire

Answer 15

• by placing a compass near a wire that is carrying current
• as you move the compass, it will trace the direction of the magnetic field

Question 16

What happens when you change direction of current of a wire with a magnetic field

Answer 16

• changing the direction of the current changes the direction of the magnetic field
• use right hand thumb rule to work out what way it goes

Question 17

What is right-hand thumb rule

Answer 17

Using right hand, point thumb in the direction of current and curl your gingers
The direction of your fingers is the direction of the field

Question 18

In a field crated by current, how does strength of field change

Answer 18

• the strength of the magnetic field produced changes with current and distance from wire
• the larger the current through the wire, or closer to the wire, the stronger the field is

Question 19

Why does magnetic field strength that a wire produces increase when wrapped into a coil called a solenoid

Answer 19

• because field lines around each loop of wire line up with each other
• this results in lots of field lines pointing in the same direction that are very close to each other

Question 20

Magnetic field inside a solenoid

Answer 20

• its strong and uniform (has same strength and direction at every point in that region)

Question 21

What is a solenoid

Answer 21

A coil of wire

Question 22

Magnetic field outside of solenoid

Answer 22

• the magnetic field is just like the one around a bar magnet
• this means the ends of the solenoid act like the north and South Pole of a bar magnet

Question 23

How to increase magnetic field of a solenoid

Answer 23

• by putting a block of iron in the centre of the coil
• the iron core becomes an induced magnet whenever current is flowing

Question 24

What happens when current of solenoid is stopped

Answer 24

• the magnetic field is appears
• solenoid with an iron core is called an electromagnet

Question 25

What is the motor effect

Answer 25

- when a current-carrying wire (or any other conductor) is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in - this causes the magnet and conductor to exert a force on each other - it can cause the wire to move

Question 26

How to experience full force of motor effect

Answer 26

- wire has to be at 90° to the magnetic field - if the wire is parallel to the ,magnetic field, it wont experience any force at all - at angles in between it’ll feel some force

Question 27

What way does the force of motor effect act in

Answer 27

- force always acts at right angles to the magnetic field of the magnets and the direction of the current in the wire

Question 28

Good way to show the direction of force in motor effect

Answer 28

- apply a current to a set of rails inside a horseshoe magnet - a bar is placed on the rails, which completes the circuit - this generates a force that rolls the bar along the rails

Question 29

How does force increase in motor effect

Answer 29

- amount of current passing through the conductor - strength of magnetic field

Question 30

What does force acting on a conductor in a magnetic field depend on

Answer 30

1. The magnetic flux density - how many field (flux) lines there are in a region. This shows the strength of the magnetic field 2. The size of the current through the conductor 3. The length of the conductor thats in the magnetic field

Question 31

When can F=BIL be used

Answer 31

When the current is at 90 degrees to the magnetic field it is in

Question 32

What is magnetic flux density and what is it measured in

Answer 32

- how many field (flux) lines there are in a region - T, tesla

Question 33

Flemings left hand rule

Answer 33

- thumb: direction of force (always north to south) - index finger: direction of magnetic field - middle finger: direction of current

Question 34

What does Flemings left hand rule demonstrate

Answer 34

- if either current or the magnetic field is reversed, then the direction of the force will also be reversed

Question 35

Explain the coil of wire rotating

Answer 35

- forces act on the two side arms of a coil of wire thats carrying a current - these forces are just the usually forces which act on any current in a magnetic field - because the coil is on a spindle and the forces act one up and one down, it rotates - the split-ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction

Question 36

How can direction of motor in rotating wire situation be reversed

Answer 36

- direction of motor can be reversed either by swapping the polarity of the dc supply (reversing the current) - or swapping the magnetic poles over (reversing the field)

Question 37

How to increase speed of motor in rotating wire situation

Answer 37

- increased speed of motor by increasing current - adding more turns to the coil - increasing the magnetic flux density