Using Magnetic Fields To Keep Things Moving

Question 1

What is the magnetic field

Answer 1

The region around the magnet in which a piece of iron or steel will be attracted to it

Question 2

What are the lines formed when iron fillings placed near a magnet form a pattern called

Answer 2

Lines of force or magnetic field lines

Question 3

A plotting compass placed in the magnetic field will always point ……

Answer 3

Along a field line

Question 4

What happens when like poles are brought together

Answer 4

The repeal each other

Question 5

What happens if unlike poles are brought together

Answer 5

The attract each other

Question 6

What is produced when a current flows through a wire

Answer 6

A magnetic field is produced around the wire

Question 7

How is an electromagnet made

Answer 7

By wrapping insulated wire around a piece of iron called the core

Question 8

What happens to the iron when a current flows through the wire

Answer 8

The iron becomes slowly magnetised

Question 9

When the current is turned off what happens to the iron

Answer 9

It loses its magnetism

Question 10

Where are electromagnets used

Answer 10

Scrapyard cranes, circuit breakers, electric bells and relays

Question 11

What is the motor effect

Answer 11

When a current is passed along a wire in a magnetic field and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by a magnetic field

Question 12

When is the force from the motor effects a maximum

Answer 12

If the wire is at 90 to the magnetic field and zero if the wire is parallel to the magnetic field

Question 13

What is Flemings left hand rule used for

Answer 13

To determine the direction of the force

Question 14

Explain the fingers in Flemings left hand rule

Answer 14

The first finger represents the magnetic field (north to south)
The second finger represents the current (pointing poz to neg)
The thumb is the direction of force

Question 15

What is the size of the force increased by

Answer 15

Increasing the strength of the magnetic field

Increasing the size of the current

Question 16

When is the direction of the force reversed

Answer 16

If either the direction of the current or the direction of the magnetic field is reversed

Question 17

How is the speed of a motor increased

Answer 17

Increasing the current

Question 18

How can the direction of the motor be reversed

Answer 18

By reversing the direction of the current

Question 19

Why does a coil spin when a current passes through the coil

Answer 19

A force acts on each side of the coil due to the motor effect
The force on one side of the coil is in the opposite direction to the force on the other side

Question 20

What does the split ring commutator do

Answer 20

Reversed the direction of the current around the coil every half turn.

Question 21

Why is the coil always pushed in the same direction in a split ring commutator

Answer 21

Because the sides swap over each half turn

Question 22

What happens if an electrical conductor cuts through magnetic field lines,

Answer 22

a potential difference is induced across the ends of the conductor

Question 23

What is electromagnetic induction

Answer 23

if a magnet is mov into a coil of wire A PD is induced across the ends of the coil. If the wire or coil is part of a complete circuit a current passes through it

Question 24

What happens if the direction of movement of the wire or polarity of the magnet is reversed

Answer 24

The direction of the induced PD is also reversed. A PD is only induced while there is movement

Question 25

How is the size of the induced PD increased

Answer 25

The speed of the movement The strength of the magnetic field The number of turns on the coil

Question 26

What does a transformer consist of

Answer 26

2 coils of insulated wire, called the primary coil and the secondary coil, which are wound into an iron core

Question 27

What happens when an ac passes through the primary coil in a transformer

Answer 27

It produces an alternating magnetic field in the core, this field continues to collapse and expand

Question 28

What happens when the alternating magnetic field lines pass through the secondary coil

Answer 28

It induces an alternating PD across its ends

Question 29

What happens if the secondary coil is part of a complete circuit and the alternating magnetic field lines pass through it

Answer 29

An alternating current is produced

Question 30

Why are the coils of wire insulated

Answer 30

So the current does not short across either the iron core adjacent turns of wire but flows around the whole coil

Question 31

What do step up transformers do

Answer 31

Make the PD across the secondary coil greater than the PD across the primary coil. It's secondary coil had more turns than its primary coil

Question 32

What do step down transformers do

Answer 32

Make the PD across the secondary coil less than the PD across the primary coil. It's secondary coil has fewer turns that it's primary coils

Question 33

What does a switch mode transformed have

Answer 33

A ferrite core

Question 34

What does a switch mode transformer do differently to traditional transformers

Answer 34

Operates at a much higher frequency Is lighter and smaller Uses very little power when there is no device connected across its output terminals

Question 35

What would happen if if transformers work with dc not ac

Answer 35

It do passes through the primary core a magnetic field is produced in the core but it would not be continually expanding and collapsing so no PD would be induced in the secondary coil

Question 36

Why does Ypres national grid use step up transformer

Answer 36

The higher the PD at which electrical energy is tenasmitted across the grid, the smaller the energy wasted in the cables

Question 37

Why are step down transformers used

Answer 37

To make the PD safe for household use

Question 38

A step down transformer has less .....

Answer 38

Turns on the secondary coil that the primary

Question 39

A step up transformer has .......

Answer 39

More turns on the secondary coil than on the primary coil

Question 40

What efficiency do transformers have

Answer 40

Almost 100%

Question 41

What does an electrocardiograph measure

Answer 41

The PD generated by the heart

Question 42

What do digital thermometers measure

Answer 42

Temperature

Question 43

What do mr scanmers do

Answer 43

Use mpradio waves to produce detailed pictures of the body

Question 44

What is endoscopy for

Answer 44

Seeing inside the body without incisions

Question 45

What are X-rays for

Answer 45

To take pictures of suspected Brocken bones

Question 46

What are cut scanners used for

Answer 46

To build up digital pictures of a cross section through the body

Question 47

What are the ends of magnets called

Answer 47

Magnetic poles