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CSEC PHYSICS > P7: Magnetism > Flashcards

P7: Magnetism Flashcards

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1
Q

only a few materials are magnetic. What elements are magnetic?

A
  • Iron
  • Nickel
  • Cobalt
  • Magnadur
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2
Q

what are dipoles?

A

atoms that behave like magnets having a north pole and a south pole

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3
Q

what is magnetic induction?

A

transfer of magnetic properties from one body to another without physical contact

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4
Q

what shows the north pole in a magnetic field?

A

the arrow heads

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5
Q

what is the only true test for polarity of a magnet and why?

A

the only true test is REPULSION. For repulsion to occur the object must already be a magnet whose nearby pole is similar to that of the other magnet.

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6
Q

what are the 2 type of magnets?

A

Temporary magnet (soft magnets) Permanent magnets (hard magnets)

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7
Q

true are false: all metals can be used to make magnets

A

false. only a few

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8
Q

list some materials used to make hard magnets

A

magnadur

alnico

ticonal

alcomax

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9
Q

list some materials used to make soft magnets

A

iron, mumental and stalloy

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10
Q

important features of magnetic field lines

A

-they never cross -the field is stronger where the lines are more concentrated and weaker where they are further apart -there is lateral repulsion between the lines -the field is uniform where the lines are parallel -they run from a north (N) pole to a south (S) pole -there is longitudinal tension within each line

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11
Q

dropping or hitting magnet will cause it to_____

A

loose some of its magnetism

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12
Q

uses of permanent magnets

A

-Loudspeakers -Directional compasses

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13
Q

simple way to make a permanent magnet.

A

rub a known magnet along the lenght of a steel bar

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14
Q

Uses of soft magnets

A

-electromagnets which are used for lifting metal objects, electric bells and electromagnetic circuit breakers

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15
Q

Attraction between magnets

A
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16
Q

repulsion between magnets

A
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17
Q

Attraction between magnetic bars that are side by side

A
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18
Q

How can the magnetic field stenght of a solenoid be increased:

A
  • using more loops of wire
  • increasing the current throught the wire
  • placing an iron core inside the solenoid
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19
Q

Repulsion between magnetic bars that are side by side

A
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20
Q

what is the direction of the field lines in a magnet?

A

north pole of the magnet to the south pole of the magnet

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21
Q

Two ways of mapping the the magnetic field of a bar magnet

A
  • using iron filings
  • using a plotting compass
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22
Q

Why does the earth have a magnetic field?

A

Its core is composed of iron and nickel which are magnetic metals.

23
Q

A directional compass always points north. Why is this so?

A

The directional compass hasa magnetic needle that will point in the direction of the earth’s magnetic field, which is from north to south, where the south corresponds the the geographical north.

24
Q

why does a directional compass point to the north pole of the earth?

A

The magnetic field lines of the earth point towards the north pole of the earth. The magnetised needle of the directional compass always points in the direction of the magnetic field lines so it will point towards the north pole of the earth.

NB the earth’s magnetic south pole core is directed towards its geographic north pole, and the magnetic north pole of the earth is directed toward its geographic south pole.

25
Q

How to identify the poles of a magnet using the earth’s magnetic field

A
26
Q

what is an electromagnet?

A

it is a temporary magnet produced when an electrical coil is placed around a soft iron core and current is passing throught the coil. Once the current stops the magnetic property is lost (temporary magnet)

27
Q

Right had grip rules for direction of magnetic field produced by electric currents

A
  1. For a wire: imagine gripping the wire with the right hand with the thumb in the direction of the current. The magnetic field will follow the direction of the other fingers from north to south
  2. For a coil: imagine gripping the coil with the right hand with the fingers in the direction of the current. The magnetic field will follow the direction of the thumb from north to south
28
Q

what is the relationship between the earths geographic poles and its magnetic poles?

A

They are the opposite of each other ie. the geographic north pole corresponds to the magnetic south pole and vice versa

29
Q

what is a solenoid?

A

a cylindrical coil of wire acting as a magnet when carrying electric current.

30
Q

Explain the motor effect?

A

a wire carrying an electric current will experience a magnetic force when placed in a magnetic field from a permanent magnet

31
Q

what are the factors affecting the force felt by a current-carrying wire in a magnetic field?

A
  1. length of the wire
  2. electric current in the wire
  3. strength of the permanent magnet
32
Q

How to find the direction of the force acting on a wire in a magnetic field?

A

Fleming’s left hand rule

33
Q

what is a d/c motor?

A

An electrical machine that converts electrical to mechanical energy

34
Q

How does the DC motor work?

A
  • coil of wire is mounted on an axle and placed between a pair of magnets where N and S poles face each other
  • The free ends of the coil is connected to a circuit by a split ring called a commutator via graphite brush contacts.
  • current is passed through the coils
  • the side near the north pole will be pushed upwards while the side near the south pole will be pushed downward according to Fleming’s rule
  • these two forces will cause the coil to rotate
  • when the coil has rotated half-turn the current will reverse making sure that the direction of the forces remains the same which keeps the coil rotating in the same direction
  • the turning moment of the coil can be used to do work
35
Q

Uses of the D/C motor

A
  • fans
  • starters
    *
36
Q

The D/C motor

A
37
Q

A/C Generator

A
38
Q

Label the diagram. What device is this?

A

A D/C Motor

A - graphite brush; B - splt-ring commutator; C - direction of force on the coil; D - D/C power source; E - magnet; F - wire coil

39
Q

Label the diagram. What device is this?

A

A/C generator

A - graphite brush; B - slip rings ; C - rotation of the coil; D - voltmeter measuring pd; E - magnet; F - wire coil

40
Q

what is a transformer?

A

A device that changes the voltage of an alternationg current

41
Q

A step up transformer has (1)_________ turns on the (2)___________ coil than on the (3)_______ coil and as a result the (4)___________ is increased while the (5)_______ is ___________ by the same (6)__________ that the voltage was decreased.

A
  1. more
  2. secondary
  3. primary
  4. voltage
  5. current
  6. factor
42
Q

A step down transformer has (1)_________ turns on the (2)___________ coil than on the (3)_______ coil and as a result the (4)___________ is decreased while the (5)_______ is ___________ by the same (6)__________ that the voltage was decreased.

A
  1. less
  2. secondary
  3. primary
  4. voltage
  5. increased
  6. factor
43
Q

what happens to the voltage in a step-up transformer

A

it increases

44
Q

what happens to the current in a step-up transformer?

A

it decreases by the same factor that the voltage was stepped up

45
Q

what happens to the voltage in a step-down transformer?

A

it decreases (is stepped down)

46
Q

what happens to the current in a step-down transformer?

A

it decreases by the same factor that the voltage was stepped down

47
Q

Is this a step-up or step down transformer?

A

step-down

48
Q

Is this a step-up or step down transformer?

A
49
Q

what is the transformer equation?

A
50
Q

true or false: the input power in a tranformer is the same as the output power

A

true

51
Q

Equation for input and output power of a transformer

A

Power = VI

VIout = VIin

52
Q

Advantages of using AC for transferring electrical energy through long distances

A
  • the volatge of AC can be easily changed to match the voltage rating of consumer electronics by using a transformer
  • AC voltage and current can be stepped up or down with little loss of energy
  • The AC can be from the power station at low current to reduce energy loss as heat
  • Thinner transfer cables can be used as the current can be stepped down, therefore reducing material cost.
53
Q

what is the main practical application of transformers?

A

Power companies use step-up tranformers to increased the voltage and decrease the current of the ac so it can be carried at larger distances with minimum resistance. Before the electricity reaches the consumer, step-down transformers decrease the voltage of the AC to appropriate values, according to the type of consumer (factories, hospitals, homes etc)

54
Q
A

CSEC PHYSICS (11 decks)

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