Chapter 12 - Electromagnetism

Question 1

Which way do the magnetic waves travel in a magnetic field ?

Answer 1

From North to south

Question 2

How can you increase the strength of a magnetic field ?

Answer 2

• increase the number of turns in the coil

- increase the current through the coil

Question 3

What is a long coil of wire referred to as ?

Answer 3

solenoid (a long coil with many turns)

Question 4

What feature does a magnetic field produce by a solenoid have ?

Answer 4

-the shape of the field is similar to that around a bar magnet and there are magnetic fields around the poles of the solenoid

Question 5

How do you carry out the right hand grip rule and what does it help you to show ?

Answer 5

• helps to show which way the poles are around on the solenoid
• grip the solenoid with your fingers going the way of conventional current. Your thumb will point towards the north pole.

Question 6

What happens when the direction of current changes in a wire ?

Answer 6

The polarity of the magnet is reversed, then the direction of the force on the wire is reversed.

Question 7

What does each finger in Fleming’s left hand rule show us ?

Answer 7

Thumb - direction of the force
Index finger - direction of the field
second finger - direction of the current

Question 8

Name two devices that use the fact that there is a force on a current-carrying wire .

Answer 8

loudspeakers and electric motors

Question 9

How can the turning affect on a coil be increased ?

Answer 9

• increasing the current in the coil
• increasing the number of turns in the coil
• increasing the strength of the magnetic field
• increasing the area of the coil

Question 10

What does the graph of voltage against time look like for a dc circuit ?

Answer 10

A constant straight line

Question 11

What does the graph of voltage against time look like for a ac circuit ?

Answer 11

Regular waves from +325v to -325v

Question 12

What’s the definition of electromagnetic induction ?

Answer 12

Producing an electrical voltage by charging the magnetic field near a conductor

Question 13

Who discovered induction ?

Answer 13

Michael Faraday

Question 14

How would you demonstrate EMI ?

Answer 14

passing a magnet through a coil of wire and placing a centre zero ammeter to measure the current

Question 15

What conditions do the magnet and solenoid need to have to a) create a current b) create no current

Answer 15

a) - one or the other has to be moving

b) - when they both are stationary

Question 16

How can you increase the size of the induced current in EMI ?

Answer 16

• moving the magnet faster
• using a stronger magnet
• using a coil with a greater amount of turns

Question 17

What did Faraday conclude from his iron ring experiment ?

Answer 17

• Closing the switch caused an increase in the current in the right-hand coil.
• this caused an increased magnetic field in the RH coil
• since the iron core links the coils magnetically the magnetic field is also increased on the LH coil
• this cause increased current to flow through the ammeter

Question 18

What is the other name for an a.c. generator ?

Answer 18

an alternator

Question 19

Look at the graph on page 176

Answer 19

It could be a potential Q !!!!

Question 20

How can you increase the size of the induced voltage of in an a.c generator ?

Answer 20

• rotating the coil faster
• using stronger magnets
• using a coil with more turns
• wrapping the coil around a soft iron core

Question 21

How many coils does a step up transformer have in it’s primary and secondary coils ?

Answer 21

Less in its primary. More in its secondary.

Question 22

How many coils does a step down transformer have in it’s primary and secondary coils ?

Answer 22

More in its primary. Less in its secondary

Question 23

What are the three parts all transformers have ?

Answer 23

• primary coil (Vp)
• secondary coil (Vs)
• laminated iron core

Question 24

What is the transformer equation ?

Answer 24

Ns / Np = Vs / Vp

Question 25

Why is electricity carried at very high voltages ?

Answer 25

It means that there is a low current in the cable and so less energy is wasted

Question 26

What must happen to the electricity before it reaches our homes?

Answer 26

It must be stepped down to 230V (much safer)