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Physics > Topic 10 - Magnetism and Electromagnetism > Flashcards

Topic 10 - Magnetism and Electromagnetism Flashcards

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1
Q

Split-ring commutator

A

A movable device that is used to swap contacts/reverse direction of current every half turn to keep the motor rotating in the same direction

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2
Q

How to reverse direction of motor

A
  • Swapping the polarity of the d.c. supply
  • Swapping the magnetic poles over
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3
Q

How to increase speed of motor

A
  • Adding more turns to the coil
  • increasing the current
  • increasing the strength of the magnetic field
  • adding a soft iron core
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4
Q

How a loudspeaker works

A
  1. alternating current changes direction
  2. current in the coil produces alternating magnetic field
  3. this produces a force on the cone
  4. reversing direction of current
  5. hence the cone oscillates
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5
Q

Dynamo effect

A

Using electromagnetic induction to generate electricity using energy from kinetic energy stores

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6
Q

Electromagnetic induction

A

The creation of a voltage (and maybe current) in a wire which is experiencing a change in magnetic field.

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7
Q

A.C. generators key points (electromagnetic induction)

A
  • power stations use a.c. generators to produce electricity
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8
Q

Transformers key points

A
  • only work with an alternating current

Mains electricity
- voltage produced by power stations is too low to be transmitted efficiently
- high current causes wires to heat up
- step-up transformer used to boost voltage before transmission
- step-down transformer used at the end of journey to reduce voltage to make it more useful and safe

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9
Q

Magnetic field line

A

A region of space where magnetic materials can experience a force. Magnetic field lines should always point from north to south.

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10
Q

Experiments to investigate magnetic field pattern

A

Experiment 1

iron filings

Experiment 2

  1. Place magnet in the centre of page and draw around
  2. Place compass at one pole of the magnet
  3. Draw a dot to show where the compass is pointing
  4. Move the compass so the opposite end of the needle is pointing to the dot
  5. Repeat steps 3 and 4 until you reach the other pole of the magnet.
  6. Join up your dots to create the field line plots
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11
Q

Describe how to use two permanent magnets to produce a uniform magnetic field pattern.

A

A uniform magnetic field is comprised of straight, parallel lines which are evenly spaced. Between two opposite charges on flat magnets, a uniform magnetic field is formed.

REFER TO DIAGRAMS TO KNOW HOW TO DRAW THE SHAPE OF B-FIELD LINES BETWEEN LIKE AND OPPOSITE POLES

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12
Q

Describe the construction of electromagnets

A

A soft iron core wrapped in wire. When current flows through the coil of wire it becomes magnetic

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13
Q

How a motor works

A
  1. Current flows in the solenoid
  2. This creates a magnetic field around the solenoid
  3. This magnetic field interacts with the field from the permanent magnet
  4. This produces a force on the solenoid, making it move
  5. The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning
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14
Q

Induced voltage and current size can be increased by

A
  • Moving the wire more quickly
  • Using a stronger magnet
  • Wrapping wire in a coil so more pieces move through the magnetic field
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15
Q

Generate voltage and current by pushing magnet into a coil (how to make faster)

A
  • Moving a magnet more quickly
  • Using a stronger magnet
  • Using a coil with more turns
  • Using a coil with larger cross-sectional area
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16
Q

How a generator works

A
  • Coil is rotated within a magnetic field
  • As it turns the coil cuts the magnetic field lines.
  • This induces a voltage (or current) in the coil.
  • This can then be connected to an existing circuit.
  • In a generator, energy is being converted from kinetic energy into electrical energy.
17
Q

How a generator (rotating magnet) works

A

magnet is dynamo
coil is generator

18
Q

Calculating magnetic force

A

F = BIL

B = magnetic field (T)
I = current (A)
L = length (m)

19
Q

How to calculate change in voltage vs number of turns on coils

A

Vp/Vs = np/ns

20
Q

P = IV modification

A

VpIp = VsIs

Physics (8 decks)

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