Chapter 12 - Electromagnetism Flashcards

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1
Q

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

A

From North to south

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2
Q

How can you increase the strength of a magnetic field ?

A
  • increase the number of turns in the coil

- increase the current through the coil

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3
Q

What is a long coil of wire referred to as ?

A

solenoid (a long coil with many turns)

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4
Q

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

A

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

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5
Q

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

A
  • 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.
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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

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

A

loudspeakers and electric motors

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9
Q

How can the turning affect on a coil be increased ?

A
  • 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
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10
Q

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

A

A constant straight line

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11
Q

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

A

Regular waves from +325v to -325v

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12
Q

What’s the definition of electromagnetic induction ?

A

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

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13
Q

Who discovered induction ?

A

Michael Faraday

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14
Q

How would you demonstrate EMI ?

A

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

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15
Q

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

A

a) - one or the other has to be moving

b) - when they both are stationary

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16
Q

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

A
  • moving the magnet faster
  • using a stronger magnet
  • using a coil with a greater amount of turns
17
Q

What did Faraday conclude from his iron ring experiment ?

A
  • 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
18
Q

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

A

an alternator

19
Q

Look at the graph on page 176

A

It could be a potential Q !!!!

20
Q

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

A
  • rotating the coil faster
  • using stronger magnets
  • using a coil with more turns
  • wrapping the coil around a soft iron core
21
Q

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

A

Less in its primary. More in its secondary.

22
Q

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

A

More in its primary. Less in its secondary

23
Q

What are the three parts all transformers have ?

A
  • primary coil (Vp)
  • secondary coil (Vs)
  • laminated iron core
24
Q

What is the transformer equation ?

A

Ns / Np = Vs / Vp

25
Q

Why is electricity carried at very high voltages ?

A

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

26
Q

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

A

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