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PHYSICS > Magnetism and electromagnetism > Flashcards

Magnetism and electromagnetism Flashcards

(52 cards)

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1
Q

Unlike poles

A

Attract

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2
Q

Like poles

A

Repel

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3
Q

Magnetic materials are only attracted to….

A

Magnetics

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4
Q

Hard magnetic materials

A
  • Steel (and other alloys of iron)
  • Hard to magnetise but do not lose their magnetism easily (hard to demagnetise)
  • Used to make permanent magnets
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5
Q

Soft magnetic materials

A
  • Soft iron
  • Easy to magnetise but are only temporarily magnetic
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6
Q

Magnetic field line

A
  • The area around a magnet that affects magnetic materials
  • Points from North to South
  • The field lines are strongest when close together
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7
Q

Uniform field

A

The strength & direction of the field is the same at all points of the field

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8
Q

Examples of magnetic materials:

A

Iron, cobalt & nickel are all attracted to magnets.

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9
Q

A permanent magnet…

A

behaves like a magnet all the time

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10
Q

When is magnetism induced in some materials

A

When they are placed in a magnetic field

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11
Q

PRACTICAL: investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets

A

To plot the shape & direction of a magnetic field

  1. Put a bar magnet in the middle of a piece of paper & draw around it
  2. Put a plotting compass on the paper so that its tail is near the end of the magnet
  3. Mark the direction the plotting compass is pointing
  4. Move the compass to the points drawn in Step 3 and repeat step 3
  5. Join the points drawn on the paper to show the shape & direction
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12
Q

To produce a uniform magnetic field

A
  • Place 2 flat magnets parallel to one another..
  • ..with opposite poles facing…
  • …close to one another, but not touching.
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13
Q

PAPER 2 When electric current flows through a long straight wire, a ………….. is produced which rotates in ………. around the wire.

A

When electric current flows through a long straight wire, a magnetic field is produced which rotates in circles around the wire

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14
Q

PAPER 2 Describe the construction of electromagnets

A

To make an electromagnet:
1. Wrap a coil of wire

  1. around an iron core
  2. Pass a current through the wire
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15
Q

Right hand thumb rule

A
  • Point the thumb of your right hand in the direction of the current
  • & the direction your fingers curl is the direction of the field
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16
Q

PAPER 2 What happens when electric current flows through a long, straight wire?

A

a magnetic field is produced which rotates in circles around the wire

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17
Q

PAPER 2 The larger the current, the ………… the field

A

Stronger

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18
Q

PAPER 2 The closer you go to the wire, the …….. the field will be

A

Stronger

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19
Q

PAPER 2 How are most electromagnets made?

A

Most electromagnets are made by passing current through a coil of wire, called a solenoid.
- The magnetic field inside the solenoid is almost uniform near the centre of the coil

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20
Q

PAPER 2 What is the magnetic field shape outside a solenoid?

A

Outside the solenoid, the fields cancel out, creating a shape similar to a bar magnet.

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21
Q

PAPER 2 What happens to the magnetic field inside a solenoid?

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A

Inside the solenoid, the magnetic fields add up, to make a strong, uniform magnetic field.

22
Q

PAPER 2 What kind of magnetic field does a moving charged particle produce?

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A

A moving charged particle produces a circular magnetic field around it.

23
Q

PAPER 2 What happens when this circular field is placed perpendicular to a uniform magnetic field?

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A

The two fields interact, creating a sideways force on both the wire and the magnet.

24
Q

What does a wire carrying current produce?

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A

a circular magnetic field around it.

25
What happens when the circular magnetic field is placed in a uniform magnetic field?
The two fields interact, and a force is applied on the opposite sides of the coil in opposite directions.
26
What happens to the coil when the two magnetic fields interact?
The coil starts to rotate due to the opposing forces on each side.
27
Explain why a force is exerted on a current-carrying wire in a magnetic field (Loudspeakers)
1. Current in coil produces magnetic field 2. field of coil interacts with field of magnet 3. producing a force on cone 4. direct of current is constantly changing because current is constantly changing because current is a.c. 5. direction of this magnetic field is (continuously) changing; 6. direction of the force changes; 7. cone vibrates; 8. air particles (next to the cone) are made to vibrate;
28
Fleming's Left Hand Rule
- If a current carrying wire is placed at 90 degrees to the field between two magnets, the wire will experience a force - The force will be at 90 degrees to the current & 90 degrees to the field of the magnets - The direction of the force can be found using ‘FLHR’, as shown in the diagram
29
Motion
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30
Field
First finger
31
Current
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32
What happens to a current-carrying wire in a magnetic field?
experiences a force
33
How can you increase the force on the wire?
- Increase the magnitude of the current. - Increase the magnetic field strength of the wire
34
What happens if you reverse the current or magnetic field?
- Reversing the direction of the current or the magnetic field reverses the direction of the force on the wire.
35
How is voltage induced in a wire?
By moving a wire through a magnetic field or changing the magnetic field around it 1. magnet (and magnetic field) moving to the right 2. potential difference induced in wire causes current to flow 3. magnetic field around wire in opposite direction to original change
36
What happens when a wire cuts a changing magnetic field?
An alternating voltage is induced
37
How do you increase the voltage induced?
- Increasing the speed of the movement - Increasing the number of turns of wire on the coil - Increasing the strength of the magnetic field
38
How is a potential difference induced in a wire?
A changing magnetic field induces a potential difference across the wire.
39
How can induced voltage be demonstrated in a lab?
By moving a bar magnet through a coil of wire.
40
How is electricity generated on a large scale?
A turbine turns a coil of wire around a magnet, inducing electricity.
41
PAPER 2 What does a transformer consist of?
A transformer consists of two coils: - A primary coil, where an AC voltage creates an oscillating magnetic field (50 Hz). - A secondary coil, where the changing magnetic field induces a voltage.
42
PAPER 2 How does a transformer induce voltage in the secondary coil?
The changing magnetic field from the primary coil passes through the secondary coil, inducing a voltage.
43
PAPER 2 What happens to the induced voltage in the secondary coil?
The induced voltage flows away from the transformer to be used in a circuit.
44
PAPER 2 How does the number of turns in the secondary coil affect voltage?
If the secondary coil has more turns, the voltage steps up (increases). If the secondary coil has fewer turns, the voltage steps down (decreases).
45
PAPER 2 What is the national grid?
A network of underground & overhead cables and transformers that connect towns to large power stations across the country.
46
PAPER 2 What is the function of a step-up transformer?
increases the voltage of electricity before it is sent through the grid
47
PAPER 2 Why does increasing voltage improve efficiency in the national grid?
Higher voltage reduces energy wasted as heat in transmission cables, making the grid more efficient.
48
PAPER 2 What is the function of a step-down transformer?
lowers the voltage to make it safe for household and consumer use.
49
PAPER 2 What is the voltage at power stations?
25 kV
50
PAPER 2 What is the voltage for household use?
230V
51
PAPER 2 What is the formula for the voltage and turns ratio in a transformer?
(Voltage across the primary coil / Voltage across the secondary coil = Number of turns in the primary coil / Number of turns in the secondary coil)
52
PAPER 2 What is the power equation for a 100% efficient transformer?
(Primary voltage × Primary current = Secondary voltage × Secondary current)

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