3- Keeping Things Moving

Question 1

What is a magnetic field?

Answer 1

The region around the magnet which will attract a piece of iron or steel

Question 2

What is a magnetic field line/line of force?

Answer 2

Iron fillings placed near a magnet form a pattern of lines that loop from one pole to the other.
Compasses point along the field line

Question 3

What is an electromagnet?

Answer 3

Insulated wire wrapped around a piece of iron (the core)
When a current flows through the wire, the iron becomes strongly magnetised because of the magnetic field produced by the wire

Question 4

Why are electromagnets useful and give examples?

Answer 4

Their magnetism can be controlled - temporary magnetism

Examples include: scrapyard cranes, circuit breakers, electric bells, relays

Question 5

What is the motor effect?

Answer 5

The force experienced by the wire when it carries an electric current in a magnetic field - at maximum of the wire is at 90* to the magnetic field (does not work when parallel)

Question 6

What does Flemings left hand rule determine and what does each finger mean?

Answer 6

The direction of the force.
The first finger: the magnetic fields direction
The second finger: the currents direction (swearing finger)
The thumb: the direction of the force

Question 7

How can the size of the motor effect force be increased?

Answer 7

Increasing the magnetic fields strength

Increasing the size of the current

Question 8

How can the direction of the motor be reversed?

Answer 8

Reversing the direction of the current

Question 9

Why does the coil spin in a motor when the current passes through it?

Answer 9

A force acts on each side of the coil (motor effect)

The force on one side of the coil is opposite to the force on the other

Question 10

What does a split ring commutator do in a motor?

Answer 10

Reverses the direction of the current around the coil every half term because of the sides swapping

Question 11

What are magnetic poles?

Answer 11

The ends of the magnet, one is North, one is South

Opposites attract and like poles repel

Question 12

What happens if an electrical conductor cuts though magnetic field lines?

Answer 12

Potential difference is induced across the ends of the conductor

Question 13

What is electromagnetic induction?

Answer 13

A magnet moves into a coil of wire inducing potential difference across the ends of the coil

Question 14

How do you reverse the direction of the induced potential difference?

Answer 14

Reverse the direction of movement of the wire

Reverse the polarity of the magnet

Question 15

How do you increase the induced potential difference?

Answer 15

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

Question 16

Describe a transformer?

Answer 16

Two coils of insulated wire (one primary and one secondary) wound onto an iron core which produces an alternating magnetic field when a current passes through it which continually expands and collapses

Question 17

What happens to the alternating magnetic field lines in a transformer?

Answer 17

They pass through the secondary coil and induce an alternating potential difference across the ends. If it is part of a complete circuit then an alternating current is produced

Question 18

Why are the coils of wire insulated in a transformer?

Answer 18

So the current does not short across either the iron core or adjacent turns of wire

Question 19

What’s the difference between a step up and step down transformer?

Answer 19

Step up makes the potential difference across the secondary coil greater than that of the primary because it’s secondary has more turns. Whereas a step down makes the potential difference greater across the primary because it has more turns

Question 20

What’s a switch mode transformer?

Answer 20

With a ferrite core, it operates at a higher frequency, it is lighter and smaller and uses very little power when decides are not connected to it

Question 21

What and why does the national grid use transformers?

Answer 21

They use them to step up the potential difference from power stations because the higher the potential difference, the less energy wasted
They use them to step down the potential difference so it is safe for consumers

Question 22

Examples of when physics is used in hospitals?

Answer 22

Blood pressure measuring
ECG recordings
Endoscopes
Scanners