Electromagnetism Flashcards

1
Q

Are magnetic forces contact or non-contact?

A

Non-contact

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2
Q

What is a magnet?

A

An object capable of exerting a magnetic force.

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3
Q

What is the difference between a permanent and an induced magnet?

A

Permanent is always magnetic whilst induced only becomes a magnet when it’s in a magnetic field. Induced can only attract.

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4
Q

Describe magnetic field lines?

A

They point from the North Pole to the South Pole and don’t cross each other. It is strongest where they are closest.

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5
Q

What is the Earth’s magnetic field caused by?

A

The iron and nickel core.

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6
Q

What is a magnetic field?

A

Area surrounding a magnet that can exert a force on magnetic materials.

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7
Q

What is a solenoid?

A

A coil of wire carrying an electrical current - its shape causes a stronger magnetic field.

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8
Q

What does an electromagnet consist of? What is an example of where they are used?

A

A solenoid with an iron core.
An electric door bell.

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9
Q

What is Flemings left hand rule used for?

A

To find the direction of a force on a conductor in a magnetic field.

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10
Q

Fleming’s left hand rule:
Thumb
Forefinger
Second finger

A

Thumb - movement
Forefinger - field
Second finger - current

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11
Q

What is a dc motor?

A

An electrical device that uses direct current to produce a turning effect.

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12
Q

What is a split ring commutator’s purpose?

A

To keep the motor rotating in the same direction by allowing the current in the coil to change direction each half-turn as the coil rotates.

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13
Q

What will increase the strength of the magnetic field around a wire carrying a current?

A

Increasing the current.

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14
Q

What is the effect of putting an iron core inside a solenoid?

A

The electromagnet becomes stronger.

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15
Q

What are poles?

A

Ends of a magnet where the magnetic forces are strongest.

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16
Q

Describe how a material becomes a magnet?

A

When a magnetic material is placed in a magnetic field, a magnetic field is induced and the material becomes a temporary magnet. When the material is removed from the magnetic fields the induced magnet loses all its magnetism.

17
Q

List some magnetic materials.

A

Iron
Cobalt
Nickel
Steel

18
Q

How can it be shown that a magnetic material is a permanent magnet?

A

It will attract and repel another magnet.

19
Q

What do the strengths and directions of magnetic fields depend on?

A

Strength - distance from the magnet
Direction - the direction of the force that would act on another north pole places at that point

20
Q

Describe how to plot the field line pattern of a bar magnet.

A
  1. Place the compass near the n pole of the magnet
    2.. Mark a small cross where the compass needle is pointing
  2. Move the compass so the South Pole of the needle touches this cross
  3. Repeat this until the South Pole if the magnet is reached
  4. Join the crosses to show the field lines
  5. Repeat for different positions from the n pole of the magnet
21
Q

Electromagnetism

A

The effect where a magnetic field is produced by result of an electric current flowing through a wire.

22
Q

Current flows from … to …

A

Positive to negative

23
Q

Magnetic field is directly proportional to …
It is inversely proportional to …

A

Current in the wire
Distance from the wire

24
Q

Describe the right hand grip rule for a wire.

A

Thumb points in the direction of the current
Fingers point in the direction of the field

25
Q

Describe the magnetic field inside and around a solenoid.

A

Inside - strong and uniform
Around - similar shape to a bar magnet’s magnetic field

26
Q

How can the strength of the magnetic field of a solenoid be increased?

A

Increasing the current
Increasing the number of turns of wire in the coil
Add an iron core inside the coil

27
Q

Describe the right hand grip rule for a solenoid.

A

Fingers curl in the direction of the current
Thumb points in the direction of the North Pole.

28
Q

What are the advantages of using an electromagnet instead of a permanent magnet?

A

They can be switched on and off which is useful for moving magnetic items
Their strength can be altered by varying the current

29
Q

How can the magnetic effect of a current be demonstrated?

A

Iron fillings can be placed near a current carrying wire. The effect on the pattern made by them gives evidence for a magnetic field.

30
Q

What willl happen when a wire carrying a current is placed south to north ina magnetic field?

A

Nothing because the current is parallel to the magnetic field and so they will not interact as they are not at right angles to each other.

31
Q

What is magnetic flux density?

A

A measure of the strength of the magnetic field. Tesla.

32
Q

Describe how an electric motor works.

A
  • when the current flows, the force acts upwards on the left side and downwards on the right side of the loop
  • this produces a clockwise movement as the left side moves up and the right moves down
  • when the loop is vertical, the force on the loop is zero and there is no movement
  • the loop has momentum and keeps moving. The split ring commutator swaps the connections with the battery so the current starts flowing again, but in the opposite direction
33
Q

Explain how a force on a wire causes a coil to rotate.

A

The current travels in opposite directions on each side of the coil of wire so the force acting in each side will be in opposite directions producing a moment on the coil.