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GSCE Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

what is current measured in?

A

amperes (A)

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2
Q

what is the definition of current

A

the rate of flow of charge at a point in the circuit

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3
Q

what is charge measured in?

A

coulombs (C)

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4
Q

why is there current in metals?

A

due to a flow of electrons

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5
Q

why is there current in solutions?

A

due to a flow of ions

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6
Q

what is conventional current?

A

the rate of flow of positive charge - this is in the opposite direction to the flow of electrons because electrons are negatively charged

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7
Q

where is current conserved in a circuit?

A

at a junction because the charge is always conserved

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8
Q

what is current measured with and where is it connected in the circuit?

A

current is measured with an ammeter connected in series with the component

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9
Q

what is potential difference measured in?

A

volts (V)

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10
Q

what is the definition of potential difference?

A

the work done per unit charge in moving between two points in a circuit

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11
Q

what is potential difference measured by and where is it connected in the circuit?

A

it is measured with a voltmeter placed in parallel across the component

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12
Q

what is the relationship between potential difference and current?

A

the higher the potential difference, the greater the current

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13
Q

what is the resistance of a component measured in?

A

ohms

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14
Q

how do you work how resistance?

A

resistance is given by the potential difference across the component divided by the current through it

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15
Q

what is the relationship between resistance and current?

A

the greater the resistance, the harder it is for current to flow through the component

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16
Q

what is an example of an ohmic conductor?

A

a resistor at a constant temperature

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17
Q

what is the relationship between current and voltage is an ohmic conductor?

A

the current is directly proportional to the voltage

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18
Q

what is an example of a non-ohmic conductor?

A

a filament lamp

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19
Q

what is the relationship between current and voltage in a non-ohmic conductor?

A

the resistance changes as the voltage and current changes

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20
Q

why does the resistance change as the voltage and current change in a filament lamp?

A
  • this is because the current increases through the filament, so does the temperature
  • this means the electrons and ions vibrate more and collide more
  • this increases resistance
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21
Q

what is a thermistor?

A

a resistor whose resistance decreases as the temperature increases

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22
Q

what is a light dependent resistor?

A

a resistor whose resistance decreases as light intensity increases

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23
Q

what are the features of a series circuit?

A
  • components are connected end to end in one loop
  • the same current flows through every component
  • the potential difference is shared across each component (depending on their resistance) so components with a higher resistance have a greater potential difference across
  • the total resistance in series is the sum of the resistance of each component
24
Q

what are the features of a parallel circuit?

A
  • components are connected to the power supply in separate branches
  • the current is shared between each branch because charge can only flow one way
  • the potential difference is the same across every branch
  • connecting lamps in parallel is advantageous because if one breaks, current can still pass through the rest
25
what are the hazards of damaged insulation?
contact with the wire due to gaps in the insulation can cause an electric show
26
what are the hazards of overheating of cables?
high currents passing through thin wire conductors cause the wires to heat up to a very high temperatures which could melt the insulation and cause a fire
27
what are the hazards of damp conditions?
water can conduct a current so wet electrical equipment can cause an electric shock
28
what is a fuse?
a thin piece of wire which overheats and melts if the current is too high, protecting the circuit - they have a current rating which should be slightly higher than the current used by the device in the circuit
29
what are the most common fuse current ratings?
3A, 5A and 13A
30
what do circuit breakers consist of?
an automatic electromagnet switch which breaks the circuit if the current rises over a certain value
31
why are circuit breakers better than fuses?
- it can be reset and used again - they operate faster
32
what do earth wires do?
they create a safe route for current to flow through in the case of a short circuit, preventing electric shocks
33
why do earth wires have very low resistance?
so a strong current surges through them which breaks the fuse and disconnects the appliance
34
why do appliances have double insulation?
they have either plastic casings completely covering their electrical components, or have been designed so that the earth wire cannot touch the metal casing, preventing them from giving an electric shock
35
what is energy measured in?
joules (J)
36
what is the electrical transfer of energy?
energy that is transferred from chemical energy in the battery to electrical energy used by circuit components and then to the surroundings
37
what is the power of a component measured in?
watts (W)
38
what is direct current?
current that only flows in one direction
39
what is alternating current?
current that continuously changes direction
40
is mains electricity alternating or direct current?
alternating current
41
is current supplied by a cell or battery alternating or direct current?
direct current
42
what types of charges are there and what are their relationships with each other?
- there are positive and negative charges - opposite charges attract and like charges repel
43
what are atoms composed of?
- protons (+1 charge) - electrons (-1 charge) - neutrons (0 charge)
44
what happens when you charge a body?
it involves the addition or removal of electrons
45
what happens when you charge atoms?
it creates ions
46
do conductors and insulators allow the flow of electrons?
- conductors such as metals allow electrons to flow through them - insulators such as plastics impede the flow of electrons
47
what happens when two insulators are rubbed together?
- friction causes electrons to move from one to the other and they become charged - the material that loses electrons becomes positively charged and the material that gains electrons becomes negatively charged
48
what is the magnitude of the charge on each material that becomes charged?
the charge on each material is equal, since they lose/gain the same number of electrons
49
what is static electricity?
when the charges cannot move within the insulator so they build up
50
how does static electricity cause lightning?
- electrostatic charge can build up on clouds due to friction - when this charge becomes large enough, the clouds discharge through the air to the earth - this results in lightning
51
how does static electricity cause a balloon to stick to the wall?
- a positively charged balloon will stick to a wall if moved close enough - positive charges in the wall are repelled by the balloon and move to other parts of the wall - this leaves a negative charge on the area of the wall closest to the balloon - the attraction between the negatively charged wall and the positively charged balloon makes the balloon stick
52
how does static electricity allow a comb to pick up bits of paper?
- rubbing a comb against an insulator will cause it to pick up an electrostatic charge due to the transfer of electrons - the charge on the comb repels like-charges in the paper, leaving the paper closest to the comb with an electrostatic charge opposite to the comb - this end of the paper is then attracted to the comb
53
what are the dangers of electrostatic charges?
- static charges pose a risk of electric shock - if a person touches an object with a large amount of static charge, electrons will flow through the persons body to the earth - when fuelling aircraft and tankers, if enough charge builds up on the vehicle or pump it can create a spark - this can ignite the fuel and cause a fire of explosion, therefore for safety, an earthing wire can be attached so that the charge instead flows into the earth
54
what are safety measures when using electrostatic charges?
- earthing involves offering electrons an alternative pathway to the earth and this prevents too much electrostatic charge from building up on the surface of an insulator - less electrostatic charge reduces the risk of an electric shock, or the harm it can cause
55
what are uses of electrostatic charges?
inkjet printer: - droplets of ink are charged and pass between two charged metal plates, one of which has a positive charge and the other a negative charge - the droplets are attracted to the plate with the opposite charge and repelled by the plate with the same charge and deflected towards a specific place on the paper photocopier: - the image of a document is projected onto a positively charged plate; where light falls onto the plate, the charge leaks away - negatively charged toner particles are attracted to the remaining positive areas - paper is then placed over the plate and the toner is transferred to it, making the photocopy

GSCE Physics (9 decks)

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