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Poppy > Using Magnetic Fields To Keep Things Moving > Flashcards

Using Magnetic Fields To Keep Things Moving Flashcards

1
Q

What is the magnetic field

A

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

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2
Q

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

A

Lines of force or magnetic field lines

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3
Q

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

A

Along a field line

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4
Q

What happens when like poles are brought together

A

The repeal each other

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5
Q

What happens if unlike poles are brought together

A

The attract each other

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6
Q

What is produced when a current flows through a wire

A

A magnetic field is produced around the wire

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7
Q

How is an electromagnet made

A

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

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8
Q

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

A

The iron becomes slowly magnetised

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9
Q

When the current is turned off what happens to the iron

A

It loses its magnetism

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10
Q

Where are electromagnets used

A

Scrapyard cranes, circuit breakers, electric bells and relays

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11
Q

What is the motor effect

A

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

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12
Q

When is the force from the motor effects a maximum

A

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

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13
Q

What is Flemings left hand rule used for

A

To determine the direction of the force

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14
Q

Explain the fingers in Flemings left hand rule

A

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

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15
Q

What is the size of the force increased by

A

Increasing the strength of the magnetic field

Increasing the size of the current

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16
Q

When is the direction of the force reversed

A

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

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17
Q

How is the speed of a motor increased

A

Increasing the current

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18
Q

How can the direction of the motor be reversed

A

By reversing the direction of the current

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19
Q

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

A

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

20
Q

What does the split ring commutator do

A

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

21
Q

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

A

Because the sides swap over each half turn

22
Q

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

A

a potential difference is induced across the ends of the conductor

23
Q

What is electromagnetic induction

A

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

24
Q

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

A

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

25
Q

How is the size of the induced PD increased

A

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

26
Q

What does a transformer consist of

A

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

27
Q

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

A

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

28
Q

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

A

It induces an alternating PD across its ends

29
Q

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

A

An alternating current is produced

30
Q

Why are the coils of wire insulated

A

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

31
Q

What do step up transformers do

A

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

32
Q

What do step down transformers do

A

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

33
Q

What does a switch mode transformed have

A

A ferrite core

34
Q

What does a switch mode transformer do differently to traditional transformers

A

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

35
Q

What would happen if if transformers work with dc not ac

A

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

36
Q

Why does Ypres national grid use step up transformer

A

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

37
Q

Why are step down transformers used

A

To make the PD safe for household use

38
Q

A step down transformer has less …..

A

Turns on the secondary coil that the primary

39
Q

A step up transformer has …….

A

More turns on the secondary coil than on the primary coil

40
Q

What efficiency do transformers have

A

Almost 100%

41
Q

What does an electrocardiograph measure

A

The PD generated by the heart

42
Q

What do digital thermometers measure

A

Temperature

43
Q

What do mr scanmers do

A

Use mpradio waves to produce detailed pictures of the body

44
Q

What is endoscopy for

A

Seeing inside the body without incisions

45
Q

What are X-rays for

A

To take pictures of suspected Brocken bones

46
Q

What are cut scanners used for

A

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

47
Q

What are the ends of magnets called

A

Magnetic poles

Poppy (12 decks)

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