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Physics GCSE > Mocks- electricity > Flashcards

Mocks- electricity Flashcards

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1
Q

Power

A

The rate of energy transfer or the amount of energy transferred per second

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2
Q

What does the power of a device depend on?

A
  • the voltage of a device

- the current of a device

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3
Q

What does the voltage across an electric device depend on?

A

the current and resistance of that device

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4
Q

P=

A

I^2/R

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5
Q

P=

A

I^2R

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6
Q

What does the amount of energy an appliance transfers depend on?

A
  • How long the appliance is switched on

- The power of the appliance

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7
Q

As electricity passes around a circuit, energy is transferred from the power source to

A

-the various components (which may then transfer energy to the surroundings)

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8
Q

As charge passes through the power supply,

A

it is given energy

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9
Q

As charge passes through each component

A

it loses some energy (transferring that energy to the component)

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10
Q

Most household appliances transfer energy from

A

AC mains

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11
Q

Different domestic appliances transfer energy from

A

batteries, such as a remote control

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12
Q

This can be to the kinetic energy of an electric motor. Motors are used in:

A
  • Vacuum cleaners - to create the suction to suck in dust and dirt off carpets
  • Washing machines - to rotate the drum to wash (or dry) clothes
  • Refrigerators - to compress the refrigerant chemical into a liquid to reduce the temperature
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13
Q

It can be used in heating devices. Heating is used in:

A
  • Toasters - to toast bread
  • Kettles - to boil hot water
  • Radiators - hot water is pumped from the boiler so the radiator can heat up a room
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14
Q

Work is done when

A

charge flows through a circuit

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15
Q

Work is equal to the

A

energy transferred

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16
Q

What does the amount of energy transferred by electrical work in a component depend on?

A
  • the current
  • the potential difference
  • the amount of time the component is used for
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17
Q

When charge flows through a resistor, the energy transferred is what makes the resistor

A

hot

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18
Q

When charge flows through a resistor, the energy transferred is what makes the resistor

A

hot

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19
Q

The energy transferred can be calculated using the equation:

A 
E= Pxt
E= I x V x t
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20
Q

The electrical energy transferred also depends on the

A

-charge
- potential difference
E = QxV

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21
Q

When charge flows around a circuit for a given time, the energy supplied by the battery is equal to

A

the energy transferred to all the components in the circuit

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22
Q

When charge flows around a circuit for a given time,

A

the energy transferred by the battery is equal to the energy transferred to all the components in the circuit

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23
Q

The power of an appliance is

A
  • The amount of energy it transfers by electrical work each second (This is normally the transfer of an electrical energy store to other energy stores, depending on the appliance)
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24
Q

Every electrical appliance has a power rating

A

-This tells you how much electricity it needs to work

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25
Q

The power rating for domestic electrical appliances is normally given on a label. This will include:

A
  • the potential difference required to make the device work (UK: 230V)
  • the frequency of the supply (UK: 50 Hz)
  • the power rating in Watts (varies for each device)
26
Q

The higher the power rating, the

A

quicker the change in stored energy (For example, a 2000 W kettle means the kettle transfers 2000 J of energy per second from one store to another)

27
Q

Care must be taken not to plug an appliance into a mains that is has a voltage that is much higher than stated on the label, for example in another country that has a higher mains voltage. This could cause

A

the appliance to fuse or set fire and become damaged

28
Q

Charging by friction

A
  • When certain insulating materials are rubbed against each other they become electrically charged.
    -The charges remain on the insulators and cannot immediately flow away
    -One becomes positive and the other negative
    -An example of this is a plastic or polythene rod being charged by rubbing it with a cloth
    -Both the rod and cloth are insulating materials
    -This occurs because negatively charged electrons are transferred from one material to the other
    The material, in this case, the rod, loses electrons
    -Since electrons are negatively charged, the rod becomes positively charged
    -As a result, the cloth has gained electrons and therefore is left with an equal negative charge
29
Q

Why does an object become negatively charged when it loses electrons and vice versa?

A
  • Electrons are negatively charged particles, whilst protons are positive and neutrons are neutral
  • This is why in a neutral atom, the number of electrons is equal to the number of protons
  • This is so the equal (but opposite) charges cancel out to make the overall charge of the atom zero
30
Q

When two charged particles or objects are close together, they

A

exert a force on each other

31
Q

What could the force be when two charged objects are close together?

A
  • Attractive (the objects get closer together)

- Repulsive (the objects move further apart)

32
Q

Whether two objects attract or repel depends on their

A

-charge

33
Q

If the charges are opposite

A

they will attract

34
Q

If the charges are the same

A

they will repel

35
Q

Attraction and repulsion between two charged objects are examples of

A

a non-contact force

36
Q

Wha is a non-contact force?

A

It is a force that acts on an object without physically being in contact with it.

37
Q

What is static electricity?

A
  • It is the stationary electric charge which is produced by friction which causes sparks, or the attraction of other small objects such as dust or hair
  • This is caused by the imbalance between negative and positive charges in two objects
  • This only works for insulators, since in conductors, the charge will move through them instead of remaining stationary
  • Static electricity and sparking is produced by rubbing surfaces which causes insulators to become charged by friction
  • This applies to solids, liquids and gases
38
Q

How are objects attracted to one another- static electricity

A
  • All objects are initially electrically neutral, meaning the negative (electrons) and positive charges are evenly distributed
  • However, when the electrons are transferred, one object becomes negatively charged and the other positively charged
  • This difference in charges leads to a force of attraction between itself and other objects which are also electrically neutral, by attracting the opposite charge to the surface of the objects they are attracted to
39
Q

Sticking a balloon to the wall

A
  • Rubbing a balloon on a woolen jumper transfers electrons onto the balloon by friction
  • The balloon is now negatively charged whilst the jumper is left positively charged
  • The wall is still neutral, however, when the balloon is placed near the wall, the positive charges in the wall are brought to the surface because they are attracted to the negative charge of the balloon
  • Since opposite charges attract, the balloon sticks to the wall from only the electrostatic attraction
40
Q

Examples of static electricity in everday life

A
  • Dust and dirt attracted to TV screens and computer monitors
  • Dust build-up on the edges of a fan
  • Clothes clinging to each other after being in a tumble dryer, especially those made of synthetic fabrics
  • Hair sticking up after pulling a hat off
  • Combing dry hair with a plastic comb and the hair stays attracted to the comb
  • A child’s hair sticking up after going down a plastic slide
  • Photocopiers use black powder to stick to white paper to create a copy of a document
41
Q

Where are static electricity conditions most common and why?

A
  • dry air conditions
  • This is because it is much harder for the charges to dissipate so they build up instead, and make static electricity more noticeable
  • Some of these can cause sparking
42
Q

Sparking

A

The build-up of electrostatic charge can be quite dangerous and can cause sparking (also known as an electric shock)
A static electric spark occurs when two objects which are charged by friction and become oppositely charged and have a surplus of electrons so large that the electrons ‘jump’ across to an object that is neutral
Since a current is the flow of electrons, this causes a small current to flow between the objects, called a spark
An example of sparking is the small electric shock felt from touching a door handle, or another person, after walking on a vinyl floor or nylon carpet with rubber shoes or whilst wearing socks

43
Q

An extreme example of sparking is

A

-Lightning

44
Q

lightning

A

In a storm, clouds move over each other causing them to become charged when electrons are transferred between them
Since the ground is neutral, the negative charge jumps to meet the positive charges on the ground creating a big spark
This is what is known as lightning

45
Q

When can sparks be dangerous?

A

Sparks can become quite dangerous and can cause a fire by igniting flammable gases and liquids, such as petrol

46
Q

A charged object creates

A

an electric field around itself

47
Q

Field Lines

A
  • point away from positive charges

- point towards negative charges

48
Q

The strength of an electric field depends on

A

the distance from the object creating the field

  • The field is strongest close to the charged object - this is shown by the field lines being closer together
  • The field becomes weaker further away from the charged object- this is shown by the field lines becoming further apart
49
Q

Objects in an electric field will experience

A
  • an electric force
  • since force is a vector, the direction of this force depends on whether the charges are the same or opposite.
  • The force is either attractive or repulsive
  • If the charges are the same (negative and negative or positive and positive), this force will be repulsive and the second charged object will move away from the charge creating the field
  • If the charges are the opposite (negative and positive), this force will be attractive and the second charged object will move toward the charge creating the field
50
Q

The size of the force depends on

A

the strength of the field at that point

51
Q

The force becomes … as the distance between the two charged objects decreases

A

stronger

52
Q

The force becomes… as the distance between the two charged objects increases

A

weaker

53
Q

The relationship between the strength of the force and the distance applies to both the force of attraction and force of repulsion. Two negative charges brought close together will have

A
  • a stronger repulsive force than if they were far apart.
54
Q

Objects with static charge create

A

an electric field in the space around them
-If other charges enter the field then they will experience an electric force, attracting or repelling them from the object

55
Q

Electric field definition

A

A region in which a charged object will experience an electric force.

56
Q

How are electric fields represented?

A

By electric field lines that are always in the direction of positive to negative

57
Q

The electric field lines for a charged, isolated sphere, such as a spherical conductor

A
  • Point away from the centre of a positive sphere

- Point towards the centre of a negative sphere

58
Q

What is a uniform electric field (between two parallel plates)

A
  • straight parallel lines from positive to negative
59
Q

What does the electric field help to explain?

A
  • non-contact force between charged objects since the electric field cannot be seen, but can be detected by another charged object that moves within that field due to the electric force
  • This is a non-contact force because the charged objects do not touch for the force to be exerted
60
Q

Van de Graff generator

A
  • A Van de Graaff generator removes electrons to produce a positive charge. A person does not have to touch the Van de Graaff generator to start feeling the effects, as static electricity is a non-contact force. This force will act on any charged particle in the electric field around the generator.
  • A person touching the dome of the Van de Graaff generator will also lose electrons and become positively charged. The same will happen to each of their hairs. Since the person, their head, and each of the hair follicles are all positively charged, the hairs will repel from the head and from every other strand causing them to stick out from the head in all directions

Physics GCSE (11 decks)

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