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11BT > Magnetism - Paper 2 > Flashcards

Magnetism - Paper 2 Flashcards

To revise magnetism (paper 2)

1
Q

What will two north poles do to each other?

A

Repel

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2
Q

What will two south poles do to each other?

A

Repel

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3
Q

What will a south and north pole do to each other?

A

Attract

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4
Q

Is mangentism an example of a contact or non contact force?

A

Non contact

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5
Q

State some differences between permanent and induced magnets

A

A permanent magnet always has a magnetic field. An induced magnet only becomes magnetic when placed in a magnetic field. Induced magnets always causes force of attraction. Permanent magnets can attract or repel.

Permanent magnets have north and south poles

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6
Q

State the magnetic materials

A

Iron, steel, cobalt, nickel

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7
Q

What do we call the region around a magnet where a force acts on another magnetic material?

A

Magnetic field

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8
Q

What do magnetic fields line show?

A

The closer the fields lines the stronger the field. The arrows show the direction of force a north pole would feel.

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9
Q

Which direction do magnetic field lines point in?

A

North to South

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10
Q

What is the relationship between the size of attraction/repulsion and distance from a magnet

A

As distance increase the force or field gets weaker

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11
Q

Where is the strength of a magnetic field the strongest?

A

The poles of a magnet

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12
Q

Why do magnetic field lines always need arrows on them?

A

The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south(seeking) pole of the magnet.

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13
Q

Describe how a magnetic compass works

A

A magnetic compass contains a small bar magnet. The Earth has a magnetic field. The compass needle points in the direction of the Earth’s magnetic field.

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14
Q

Describe how a magnetic compass can be used to find the pattern around a bar magnet.

A

Put the magnet in the middle of the piece of paper and draw around it. Draw nine dots around the north end of the magnet. Put a plotting compass on the paper so that its tail is over one of the dots. Draw a dot on the paper near to the point of the compass. Join the two dots and mark the line with an arrow. Then move the compass so that its tail is over your new dot. Make another dot next to the point. Repeat until you come to the edge of the paper or loop back round to the south pole.

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15
Q

When a current flows what is always created?

A

A magnetic field

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16
Q

What factors affect the strength of the magnetic field produced by a current?

A
  1. Size of the current 2. Distance from the wire
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17
Q

What is a solenoid?

A

When a current carrying wire is turned into a coil. this will increase the strength of the magnetic field.

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18
Q

Describe the magnetic field inside a solenoid

A

The magnetic field inside a solenoid is strong and uniform.

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19
Q

Describe the magnetic field around a solenoid

A

The magnetic field around a solenoid has a similar shape to that of a bar magnet.

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20
Q

How can a solenoid be turned into an electromagnet?

A

Adding an iron core, this again increases the strength of the magnetic field.

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21
Q

Describe the magnetic field of an electromagnet

A

Its the same as a bar magnet

22
Q

How can the strength of an electromagnet be increased?

A

Larger current More turns Using an iron core

23
Q

Describe the magnetic field produced by a straight wire carrying a current

A

circular rings around the wire. the right hand rule shows the direction of the magnetic field

24
Q

Describe the right hand rule for a straight wire carrying a current

A

Thumb points in the direction of the current, fingers curl around in the direction of the magnetic field

25
Q

What is the motor effect?

A

When a conductor carrying a current is placed in a permanet magnetic field the magnet the two magnetic fields exert a force on each other.

26
Q

Describe Fleming’s left hand rule.

A

Thumb, first finger and second finger are put at right angles to each other. Thumb - direction of force/motion First Finger - direction of magnetic field (always from North to south) seCond finger - direction of current (always from positive to negative)

27
Q

In the motor effect how can the size of the force be increased?

A

Larger current Stronger permanent magnets Longer length of wire inside the magnetic field Keeping the conductor at a right angle to the magnetic field

28
Q

In the motor effect how can the direction of the force be reversed?

A

Reversing the direction of the current Reversing the poles of the permanent magnets

29
Q

State the units for magnetic flux density.

A

Tesla (T)

30
Q

Describe how a coil of wire inside a magnetic field can cause rotation eg an electric motor

A

The current goes into the coil of wire, creating an electromagnetic field. This interacts with a the permanent magnetic field causing a force of attraction or repulsion. the current then comes out of the coil changing direction so the force changes direction. This causes rotation.

31
Q

How do loudspeakers/headphones use the motor effect to create sound waves.

A

A coil of wire is wrapped around a permanent magnet. An alternating current passes through the wire creating an electromagnetic field. the magnetic field from the current and permanent magnetic interact causing a force of attraction or repulsion. As the current is a.c. the force changes between attraction and repulsion. This causes the loud speaker cone to vibrate which creates sound waves.

32
Q

What is magnetic induction?

A

If an electrical conductor moves relative to a magnetic field or if there is a change in the magnetic field around a conductor, a potential difference is induced across the ends of the conductor.

33
Q

What are the four conditions required for magnetic induction?

A

A magnetic field

A conductor

Movement

A complete circuit

34
Q

When will magnetic induction create a current?

A

If the conductor is part of a complete circuit, a current is induced in the conductor. This is called the generator effect.

35
Q

State some factors that can increase the size of the induced potential difference

A

Faster movement More turns of wire Stronger magnet

36
Q

State some factors that can reverse the direction of the induced potential difference

A

Reverse the direction of movement Change the pole of the magnet

37
Q

Describe how microphones use induction/generator effect to turn sound waves into electricity

A

A microphone has a cone that is attached to a coil of wire wrapped around a permanent magnet. As a sound wave hits the cone it causes the cone and coil and wire to vibrate up and down. A conductor is now moving through a magnetic field so an induced potential difference is created. As the coil of wire is part of a complete circuit then an induced current is created.

38
Q

What is an a.c. generator also known as?

A

An alternator

39
Q

What is a d.c. generator also known as?

A

A dynamo

40
Q

Describe how an ac generator (alternator works)

A

An alternator is a coil or wire inside a permanent magnetic field. the coil of wire is made to rotate inside the magnetic field. As the coil of wire cuts through the magnetic field an induced potential difference is created. As the coil is part of a complete circuit an induced current flows. As the coil is constantly changing direction the induced potential difference and induced current is constantly changing direction as well.

41
Q

Why does an alternator produce an a.c. output?

A

the two sides of the coil are always connected to the same side of the lamp. when the LHS of the coil moves past the top it reverses the direction of movement so voltage and therefore current reverses

42
Q

Describe the differences between an ac generator (Alternator) and a d.c. generator (Dynamo)

A

A dynamo works in the same way as an alternator except that a a dynamo has a split ring commutator instead of two separate slip rings. As the coil spins the split ring commutator reconnects the coil the opposite way around every half turn. This means the potential difference doesn’t reverse its direction. The p.d. will vary from zero to a maximum twice each cycle but never changes polarity.

43
Q

Why does a dynamo produce a d.c. output?

A

the two sides the coil are connected to split rings so the two sides of the coil are not connected to the same side. during a turn every half turn the connections are reversed so when induced voltage is reversed, the current flowing is not reversed

44
Q

Describe the structure of a transformer

A

An insulated primary coil and an insulated secondary coil wrapped around an iron core.

45
Q

Why is iron used in transformers?

A

Iron can be easily magnetised and demagnetised.

46
Q

Describe the role and design of a step up transformer.

A

A step up transformer increases the output voltage. it does this by having more turns of wire on the secondary side.

47
Q

Describe the role and design of a step down transformer.

A

A step down transformer decreases the output voltage. It does this by having less turns of wire on the secondary side.

48
Q

Explain how a transformer works

A

a.c. flows in primary coil. This creates an alternating magnetic field in primary coil. Magnetic field from primary coil cuts through secondary coil via the iron core. This induces a potential difference and current in the secondary coil. Current in secondary coil is also a.c.

49
Q

Do transformers work with a.c. or d.c.?

A

Only a.c. the magnetic field must be moving through the secondary coil to induce a potential difference

50
Q

When using the transformer equation what assumption is made?

A

They are 100% efficient so the power on the primary coil is equal to the power on the secondary coil.

51
Q

Describe the role of a microphone

A

To convert sound waves into variations in current

11BT (18 decks)

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