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Electromagnetism Flashcards

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1
Q
  1. What is created around a wire when current flows through it?
A
  1. A magnetic field is created around the wire.
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2
Q
  1. How is the direction of the magnetic field determined around a wire?
A
  1. The direction of the magnetic field is determined by the direction of the current.
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3
Q
  1. What happens when iron fillings are sprinkled on a card board with a vertical wire passing through its center and current flows through the wire?
A
  1. The iron fillings arrange themselves in concentric circles when the board is tapped, showing a magnetic field around the wire.
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4
Q
  1. What does the closeness of concentric circles near a wire indicate in a magnetic field experiment?
A
  1. It indicates that the magnetic force is stronger near the wire.
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5
Q
  1. What does the Right Hand Grip Rule state?
A
  1. If a wire is held in the right hand with the thumb pointing in the direction of the current, the other fingers point in the direction of the magnetic field.
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6
Q
  1. What does Maxwell’s Corkscrew Rule state?
A
  1. If the right hand is used to screw a corkscrew along a wire in the direction of the current, the direction of the rotation of the screw gives the direction of the magnetic field.
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7
Q
  1. What symbol is used to represent a straight wire carrying current into a paper?
A
  1. A cross (X) is used.
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8
Q
  1. What symbol is used to represent a straight wire carrying current out of a paper?
A
  1. A dot (•) is used.
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9
Q
  1. What is an electromagnet?
A
  1. An electromagnet is a magnet produced when a magnetic material is placed in a solenoid carrying current.
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10
Q
  1. What effect does increasing the number of turns of a solenoid have on the strength of an electromagnet?
A
  1. It increases the strength of the electromagnet.
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11
Q
  1. How does the amount of current flowing through a solenoid affect the strength of an electromagnet?
A
  1. Increasing the current flowing through the solenoid increases the strength of the electromagnet.
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12
Q
  1. Why is soft iron often used in electromagnets?
A
  1. Soft iron is easily magnetized and easily demagnetized, making it ideal for electromagnets.
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13
Q
  1. What shape of magnetic material produces a stronger electromagnet?
A
  1. A horse-shoe shape produces a stronger electromagnet because the poles are close to each other.
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14
Q
  1. Name three applications of electromagnets.
A
  1. Lifting magnets, electric bells, and telephone receivers.
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15
Q
  1. How are electromagnets used in steel industries?
A
  1. Electromagnets are used for lifting and transporting heavy steel from one place to another in a factory.
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16
Q
  1. What are the key components of an electric bell?
A
  1. A hammer, gong, soft iron armature, contact adjusting screw, push switch, steel spring, and an electromagnet.
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17
Q
  1. What happens when the switch of an electric bell is pressed?
A
  1. Current flows, magnetizing the soft iron core (electromagnet), which attracts the armature, causing the hammer to hit the gong, producing a sound.
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18
Q
  1. How does a telephone receiver convert sound energy?
A
  1. It converts sound energy into electric current, which then passes through a solenoid, magnetizing the soft iron and causing the diaphragm to vibrate, reproducing the sound.
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19
Q
  1. What is a magnetic relay used for?
A
  1. A magnetic relay is used as a switch that uses a small current in a primary circuit to turn on or off a larger current in a secondary circuit.
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20
Q
  1. How does a circuit breaker operate?
A
  1. When current increases, the electromagnet becomes stronger and pulls the soft iron armature, disconnecting the circuit and stopping the current flow.
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21
Q
  1. What is the motor effect?
A
  1. The motor effect is when a conductor carrying current experiences a force when placed across a magnetic field.
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22
Q
  1. What happens when a current-carrying conductor is placed across a magnetic field?
A
  1. The magnetic field due to the current interacts with the magnetic field of the permanent magnet, producing a force on the conductor.
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23
Q
  1. What does Fleming’s Left Hand Rule state?
A
  1. If the left hand is held with the thumb, first finger, and second finger at right angles to each other, the thumb points in the direction of force, the first finger in the direction of the magnetic field, and the second finger in the direction of current.
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24
Q
  1. What is observed when current flows in the wire in the direction AB between the poles of a permanent magnet?
A
  1. The wire moves upwards.
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25
Q
  1. What happens when current flows in the opposite direction, from BA, between the poles of a permanent magnet?
A
  1. The wire moves downwards.
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26
Q
  1. How does the amount of current affect the magnitude of force on a current-carrying conductor?
A
  1. Increasing the amount of current increases the magnitude of the force.
27
Q
  1. How does the strength of a magnetic field affect the magnitude of force on a current-carrying conductor?
A
  1. Increasing the strength of the magnetic field increases the magnitude of the force.
28
Q
  1. What effect does increasing the length of a conductor have on the force exerted on it in a magnetic field?
A
  1. Increasing the length of the conductor increases the magnitude of the force.
29
Q
  1. What effect does increasing the cross-sectional area of a conductor have on the force exerted on it in a magnetic field?
A
  1. The larger the cross-sectional area of the conductor, the larger the force created.
30
Q
  1. What happens when the magnetic field and current are parallel to each other in a conductor?
A
  1. No force is exerted on the conductor.
31
Q

What happens when a conductor moves across a magnetic field and cuts the magnetic flux?

A

An emf/current is induced in the conductor.

32
Q

Define electromagnetic induction.

A

Electromagnetic induction is the process by which an emf is induced in the coil due to a change in magnetic flux linking the coil.

33
Q

What factors determine the magnitude of the induced emf/current?

A

Number of turns, strength of the magnet, area of the coil in the magnetic field, and rate at which magnetic flux changes.

34
Q

How does increasing the number of turns in a coil affect the induced emf?

A

The magnitude of induced emf is increased by increasing the number of turns of the coil.

35
Q

How does using a stronger magnet affect the induced emf?

A

The magnitude of induced emf can be increased by using a strong magnet to provide a stronger magnetic field.

36
Q

How does placing a larger area of coil into a magnetic field affect the induced emf?

A

The magnitude of induced emf is increased by placing a large area of coil into the magnetic field.

37
Q

What is Fleming’s right-hand rule used for?

A

To find the direction of the induced current in a conductor moving through a magnetic field.

38
Q

What does Fleming’s right-hand rule state about the thumb, first finger, and second finger?

A

Thumb points in the direction of force (motion), the first finger points in the direction of the magnetic field, and the second finger points in the direction of the induced current.

39
Q

State Faraday’s law of electromagnetic induction.

A

The magnitude of induced emf in a coil is directly proportional to the rate of change of magnetic flux linking the coil.

40
Q

State Lenz’s law.

A

The induced current flows in a direction so as to oppose the change causing it.

41
Q

Describe the experiment to verify Lenz’s law.

A

Move a magnet with its south pole facing towards a solenoid connected to a galvanometer and observe the direction of the induced current.

42
Q

What happens to the galvanometer when a magnet is moved into a solenoid?

A

The galvanometer deflects to the left, showing that the induced current flows in a clockwise direction.

43
Q

What happens to the galvanometer when a magnet is pulled out of a solenoid?

A

The galvanometer deflects to the right, showing that the induced current flows in an anticlockwise direction.

44
Q

How can the magnitude of the current induced in a coil be increased?

A

By increasing the number of turns of the coil, using a stronger magnet, or increasing the speed at which the magnet is moving.

45
Q

What is a generator?

A

A device that converts mechanical energy into electrical energy.

46
Q

Name the two types of generators.

A

Direct current generator (dynamo) and alternating current generator (alternator).

47
Q

What are the components of a D.C. generator?

A

Permanent magnets, an armature/rectangular coil, and carbon brushes with split rings (commutators).

48
Q

Describe the mode of operation of a D.C. generator.

A

The rectangular coil rotates, changing magnetic flux and inducing emf. Split rings reverse current direction to maintain consistent output.

49
Q

How is an A.C. generator different from a D.C. generator?

A

An A.C. generator uses slip rings instead of split rings to provide continuous direction change in the current.

50
Q

What are the two types of induction?

A

Self-induction and mutual induction.

51
Q

What is self-induction?

A

The process by which an emf is induced in a coil due to changing current in the same coil.

52
Q

What is mutual induction?

A

The process by which an emf is induced in one coil due to changing current in a nearby coil.

53
Q

What is a transformer?

A

An electric device used to step up or step down alternating voltage.

54
Q

What is the structure of a transformer?

A

It consists of a laminated soft iron ring around which primary and secondary coils are wound.

55
Q

What happens when alternating voltage is applied to the primary coil of a transformer?

A

Alternating current creates a changing magnetic flux in the primary coil, inducing emf in the secondary coil.

56
Q

What is a step-up transformer?

A

A transformer with more turns in the secondary coil than in the primary coil.

57
Q

What is a step-down transformer?

A

A transformer with fewer turns in the secondary coil than in the primary coil.

58
Q

How can energy losses in a transformer be minimized?

A

By using low resistance wires, laminated soft iron cores, easily magnetized and demagnetized materials, and efficient core designs.

59
Q

What are the uses of eddy currents?

A

They are used in electromagnetic brakes and to detect cracks in metals.

60
Q

How is the efficiency of a transformer calculated?

A

Efficiency = (Power output / Power input) × 100%

61
Q

Calculate the number of turns on the secondary coil of a transformer if the primary coil has 2000 turns and the primary voltage is 240V while the secondary voltage is 12V.

A

Secondary turns = (Primary turns × Secondary voltage) / Primary voltage = (2000 × 12) / 240 = 100 turns.

62
Q

For a transformer with 80% efficiency and an output power of 12W, calculate the input current if the input voltage is 240V.

A

Input power = 12W / 0.8 = 15W; Input current = 15W / 240V = 0.0625A.

63
Q

In a transformer with 1200 turns in the primary coil and 60 turns in the secondary coil, calculate the voltage across the secondary coil if the primary voltage is 240V.

A

Secondary voltage = (Secondary turns / Primary turns) × Primary voltage = (60 / 1200) × 240V = 12V.

64
Q

For a transformer with an efficiency of 80% and a power input of 60W, calculate the current in the primary coil if the primary voltage is 240V.

A

Output power = 60W × 0.8 = 48W; Primary current = 60W / 240V = 0.25A.

Physics (7 decks)

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