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iGCSE Physics > Magnetism and Electromagnetism > Flashcards

Magnetism and Electromagnetism Flashcards

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1
Q

Define Magnetic field

A

Region where magnetic materials experience a force

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2
Q

In which direction do the magnetic field lines go?

A

From north to south

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3
Q

Define uniform field

A

Where the field strength (or the force experienced by an object) is the same at every point in the field.

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4
Q

Practical with magnetic fields

A

Place a magnet underneath a piece of paper and scatter iron filings on top to reveal a magnetic field pattern. Tap the paper gently.
Place compass needles tip-to-tail near a magnet. Record their orientations, to plot the magnet’s field as continuous field lines.

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5
Q

How can magnetism be induced?

A

If a magnetic material is brought near a magnet, it will act as a magnet. The closer they are, the stronger the induced magnetism will be.

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6
Q

Does electricity create magnetism?

A

Yes. When an electric current flows through wire it will be magnetic.

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7
Q

2 facts about currents in wires

A

-The larger the electric current, the stronger the magnetic field
-The direction of the magnetic field depends on the direction of the current.

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8
Q

Magnetism in a straight wire

A

Concentric circles

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9
Q

Magnetic field around a flat circular coil.

A

-The magnetic field in the centre is similar to a bar magnet
-Concentric ellipses of magnetic field lines around the coil.

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10
Q

Magnetic field around a solenoid

A

-Strong and uniform
-Outside of the coil, the field is like the one around a bar magnet.
-The ends of a solenoid act like the north pole and south pole.
-Electromagnet.

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11
Q

What makes a magnetic material soft or hard?

A

Soft- loses its induced magnetism quickly
Hard- keeps it permanently
-You can increase the strength of a magnetic field around a solenoid by adding a magnetically soft iron core through the middle of the coil.

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12
Q

Define the motor effect

A

It can happen when you put a current-carrying wire in a magnetic field.

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13
Q

Why does the motor effect occur?

A

When a current-carrying wire is put between magnetic poles, the two magnetic fields affect one another. The result is a force on a wire (it may move. The charged particles moving through a magnetic field will experience a force, as long as they’re not moving parallel to the filed lines.

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14
Q

What happens when you reverse the direction of the current or magnetic field?

A

It reverses the direction of the force.

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15
Q

In the left hand rule, what does each finger represent

A

Thumb=Direction of force
Index=Field
Middle=Current

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16
Q

Define Electromagnetic induction

A

Creation of voltage in a wire which is experiencing a change in magnetic field

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17
Q

Define the dynamo effect

A

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

18
Q

What are 2 ways in which you can get EM induction?

A
  1. Electrical conductor moves through magnetic field.
  2. Magnetic field through an electrical field changes.
19
Q

What does each part of the hand represent in the right-hand rule

A

Thumb=Direction of current
Hand= Magnetic field

20
Q

What ‘types’ of energy does the chemical energy stores in Power Stations.

A

Chemical energy store→Thermal energy store→Kinetic energy store→Kinetic energy store. Then transferred away electrically.

21
Q

Explain the process of creating electricity in power stations.

A
  1. Fossil fuel burns in oxygen.
  2. The energy in its chemical energy store is transferred to the thermal energy store of the water by heating.
  3. Water boils and forms steam, turns the turbine, transferring energy mechanically to the kinetic energy store of the turbine.
  4. Turbine revolves, so does the generator. Produces an electric current. The generator transfers energy electrically away from the station via the national grid.
22
Q

What type of current do transformers use?

A

Alternating current, so it is constant.

23
Q

Describe a transformer

A

They have two coils, the primary and the secondary, joined with an iron core.

24
Q

Describe the ratio between the voltages and the number of turns

A

The ratio between the primary and secondary voltages is the same as the ratio between the number of turns on the primary and secondary coils.

25
Q

What are step up transformers like? What do they do?

A

They increase the voltage. They have more turns on the secondary coil that the primary coil.

26
Q

What are step down transformers like? What do they do?

A

Decrease the voltage. They have more turns on the primary than the secondary.

27
Q

What’s the difference between the primary and secondary coils.

A

Primary= Connected to power source
Secondary= Induced electromagnetism.

28
Q

Transformer equation

A

V1/V2=N1/N2
(Input Prim voltage/Output sec voltage = number of turns on prim/Number of turns on sec).

29
Q

Power supply formula

A

P=IV

30
Q

Input power=Outfut power formula.

A

V1I1=V2I2

31
Q

What happens to the electricity before reaching your house?

A

A step down transformer reduce voltage so its more useful and safer.

32
Q

What is a hard magnet?

A

They get magnetised when an external magnetic field is applied and stay magnetised permanently when the external field is removed

33
Q

What is soft magnetic material?

A

They get magnetised when an external magnetic field is applied but they get demagnetised when the external field is removed

34
Q

What is the relationshin (directionwise), between current, magnetic field and force?

A

They all act perpendicular to eachother

35
Q

How do loudspeakers work?

A

-Coil inside a magnet
-AC is in the coil causes a magnetic field
-When the field interacts with the magnet, the motor effect happens
-Force pushes and pulled the wire/cone of the speaker, causing it to move in diff directions
-Due to AC, the force causes the cone to vibrate
-This causes pressure variations in the air

36
Q

How do microphones convert sound into electrical signals?

A

-When sound is produced, the pressure vibrations in the waves cause the diaphragm to vibrate
-A coil of wire is connected to the diaphragm, so as the diaphragm moves, so does the coil of the wire
-The coil of wire is in a magnet so when it moves a voltage is induced.
-As there is a complete circuit a current is also created

37
Q

How are electric motors kept rotating

A

Commutator. Switches the direction every half turn which ensures that the coil keeps spinning.

38
Q

How is electromagnetic induction used in alternators to generate alternating current?

A

A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means ac is produced.

39
Q

What is a solenoid

A

A coil of wire which turns into an electromagnet when there is a current flowing through it

40
Q

How can you make a magnetic field in a solenoid stronger

A

-Increase current
-More turns of wire
-Use iron core

41
Q

Importance of step up transformers

A

Increase efficiency as it decreases the head loss in transmission lines. This is because for the same power, a higher voltage will lead to a lower current (P=IV). The lover the current, the less energy that is lost since P=IR

iGCSE Physics (8 decks)

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