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Year 11 Physics GCSE > Topic 4 - Electricity > Flashcards

Topic 4 - Electricity Flashcards

1
Q

what causes a current to flow

A

a source of potential difference (voltage)

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2
Q

what is an electrical current

A

is the flow of electrical charge (spersifically electrons with a negative charge in metals)

a flow of charged particles

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3
Q

how do we calculate the charge flowing through a circuit

A

charge flow = current x time
Q = It

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4
Q

how can we describe the current at different points in a closed loop

A

a current has the same value at any point in a single closed loop

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5
Q

What are the currents in a circuit dependent on

A

the current depends on the resistor of the potential difference across the component, the greater the resistor of the component the smaller the current for a given potential difference

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6
Q

how would we calculate the current flowing in a circuit

A

current = potential difference/ resistance
I = v/r

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7
Q

how could we experimentally determine the relationship between the length of a wire and its resistor

A

the resistance of a length of wire at a constant temperature

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8
Q

how is current related to potential difference for an Ohmic conductor

A

a constant temperature is directly proportional to the potential difference across the resistor, this results in the resistor remains constant as the current changes

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9
Q

What happens to the resistance of a filament lamp as the temperature changes

A

the resistance of a filament lamp increases as the temperature of the filament increases

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10
Q

what does a diode do

A

the current through a diode only allows the current to flow in one direction only, the diode has a very high resistance in the reverse direction

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11
Q

How does the resistance of a thermistor change

A

the resistor of a thermistor decreases as the temperature increases

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12
Q

how could we use the changing resistance of a thermistor (examples)

A

example: fridge
- when it warms up the resistance decreases and the current increases
- when it cools down the resistance increases and the current decreases

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13
Q

how does the resistor of an LDR (light, dependant, resistor) change

A

the resistance of an LDR decreases as light intensity increases

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14
Q

how could we use the changing resistance of an LDR?

A
  • automatic brightness setting of phone
  • automatic security lights
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15
Q

how would we use a circuit to determine the resistance of a component

A

to determine the resistance of a component, build a circuit with an ammeter in series and a voltmeter in parallel across the component

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16
Q

what are the rules for current, potential difference and resistance for componenets connected in series?

A
  • the current is the same through each component
  • the total potential difference of the power supply is shared between the components
  • the total resistance of two compenents is the sum of the resistance of each component
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17
Q

what are the rules for current, potential difference and resistance for components in parallel

A
  • the total current through the whole circuit is the sum of the currents through each branch
  • the potential difference across each component is the same
  • the total resistance of two resistors is less than the resistance of the smallest individual resistor
18
Q

what is the difference between AC and DC

A

AC= alternating current - switches direction periodically

DC= direct current - continouusly travels in the same direction

19
Q

what is the magnitude and frequency of the Uk mains supply

A

the uk mains potential difference is about 230V and the AC frequency is 50Hz

20
Q

how is a uk three pin plug wired

A

most electrical appliances are connected to the mains using three core cable

21
Q

why is the earth pin in a uk plug the longest of the three

A

because when plugged in, it makes contact first so that the circuit is automatically earthed before connecting the main part of the circuit

22
Q

why are the pin in a plug made from brass

A

brass is hard wearing and does not oxidise (rust)

23
Q

what is the function of the fuse in the Uk plug

A

the fuse is connected to the live wire, if too much current passes through it, the fuse melts and breaks the connection to the live wire

24
Q

why are the wires in a plug made from copper

A

copper is a very good conductor and is flexible

25
Q

why are plugs and cables made from plastic

A

plastic is a good insulator so if anyone touches the plug/cable it stops them from getting a electric shock

26
Q

where might you use a two core cable

A

in an appliance that has a plastic case that cannot become live if there is a fault

27
Q

where is it totally necessary to use a three core able

A

in an appliance with a metal case, if there is a fault, the case can become live and there would be a risk of electric shock to the user

28
Q

what is a short circuit

A

where a contact is made between live and neutral wire unitentionally and cuts out part of the circuit, a large current flows by passing the intended part of the circuit

29
Q

what are the functions of the three wires in a uk plug

A
  • live wire - brown - carried alternating potential difference from the supply
  • neutral wire - blue - completes the circuit providing a path to the suppply
  • earth wire - green and yellow stripes - a safety wire to stop the appliance becoming live
30
Q

what are the potential differences of the wires in a uk plug

A
  • the earth wire is at 0V, and only carries a current if there is a fault
  • the neutral wire is 0V
  • the potential difference between the live and earth wire is about 230V
31
Q

is the live wire dangerous

A

even if a switch in the mains circuit is open, the live wire is still dangerous, providing any connection between the live and the earth results in a current flowing and this can result in an electric shock

32
Q

how could you calculate the power transfered in a circuit

A

power = current x potential difference

33
Q

how could you calculate the energy transfered in circuit

A

energy = power x time
energy = charge flow x potential difference

34
Q

What is ohms law

A

the current through a resistor at constant temperature is directly proportional to the potential differece across the resistor

35
Q

What three wires are in plugs

A

earth wire (green and yellow), live wire (red) and neutral wore (blue)

36
Q

what do all three wires do in a plug

A
  • Earth wire: carries current if there is a fault, is important for metal devices - plastic devices only need two wires
  • Live wire: deliveres the current (230v)
  • Neutral wire: completes the circuit (Ov)
37
Q

what is the equation for current?

A

current = potential difference / resistance

38
Q

what is in a series circuit

A

single path for current to flow

39
Q

what is in a parralel circuit

A

multiple paths connected with junctions

40
Q
A

Year 11 Physics GCSE (3 decks)

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