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GCSE AQA Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is a fuse?

A

a safety device which melts to break the circuit if the electrical current flowing through it exceeds a specified value

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2
Q

what is a thermistor?

A

an electrical device whose resistance decreases as the temperature increases

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3
Q

what is current?

A

a flow of electric charge

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4
Q

the greater the rate of flow….

A

the higher the current

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5
Q

equation for charge , current and time

A

charge (Columbus) = current (amperes) x time (seconds) Q=IT

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6
Q

potential difference

A

the force that pushes the charge round

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7
Q

resistance

A

anything that slows flow down

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8
Q

the greater the resistance across a component ………….

A

the smaller the current that flows

The more difficult it is for the charge to flow

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9
Q

two factors that current depends on

A

1) potential difference 2) resistance

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10
Q

the bigger the potential difference across a component …

A

the greater the flow of charge through the component the bigger the current

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11
Q

Equation for potential difference

A

current x resistance V= IR

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12
Q

What’s an ohmic conductor?

A

a device that obeys ohms law

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13
Q

What’s Ohm’s Law?

A

V=IR

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14
Q

What are I-V characteristics?

A

Graphs which show how the Current changes with Voltage in a components

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15
Q

shallow gradient in a I-V graph means

A

high resistance -large potential difference needed to produce a small amount

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16
Q

what does it mean when a straight line cuts through the origin

A

that the current and voltage are directly proportional

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17
Q

steep gradient in a I-V graph means

A

low resistance - large current will flow though a small voltage (large voltage not needed)

18
Q

list four components for which the resistance is not constant due to the current changing

A

1) lamps 2) diodes 3)thermistor 4) LDR (light dependant resistor)

19
Q

filament lamps

A

As the current through a filament lamp increases, its temperature increase. This causes the resistance to increase as the current increases. It is indicated by a curved graph.

20
Q

Diodes

describe its graph as well

A

current flows through only one direction high resistance if current is reversed

21
Q

LDR

A

dependant on light intensity

bright = resistance falls

darkness = resistance increases

22
Q

What is a variable resistor?

A

a resistor where the vaue of the resistance can be changed

23
Q

what is a light emitting diode?

A

only allows current to flow in the forward direction and emits light when current flows through them

24
Q

What is the rule for voltage, current and resistance in series circuits?

A

voltage is shared

Vtotal = V1 + V2 + ……….

Current is the same everywhere

I = V/R

Resistance adds up

Rtotal = R1 + R2 + ……….

25
Q

how must voltmeters and ammeters be connected

A

ammeters should always be connected in series

voltmeters should always be connected in parallel

26
Q

What is the rule for voltage, current and resistance in parallel circuits?

A

Voltage is the same across all components

current is shared between branches

Adding a resistor reduces the total resistance

27
Q

why does adding resistors in parallel reduces the total resistance?

A

Because, in parallel, there are more paths for the current to take, allowing it to flow more easily

28
Q

the equation for power in a circuit?

A

P = voltage x current

p = current 2 x resistance

29
Q

What is a direct current supply?

A

current that flows in one direction

  • has a potential difference that is always positive or negative
  • the type of current that is supplied by batteries and cells
30
Q

What is an alternating current supply?

A
  • the current is always changing direction
  • has a potential difference that alternates from positive to negative
  • used in mains electricity
31
Q

What is the UK mains electricity and how many times does it change directions per second?

A

230V

changes direction 50 times per second therefore it has 50Hz

32
Q

the 3 different wires in a three-core cable are:

A
  • live wire (brown)
  • neutral wire (blue)
  • earth wire (green and yellow stripes)
33
Q

What does the live wire do?

A
  • provides the alternating current (at about 230V) from the mains supply

-

34
Q

What does the neutral (blue) wire?

A
  • completes the circuit and carriers away current
  • it is around 0V
35
Q

What does Earth Wire do?

A
  • for protecting the wiring and for safety
  • stops the appliance casing from becoming live
  • The earth wire is at 0 V, it only carries a current if there is a fault.
36
Q

What happens inside a three-core cable during operation?

A
  • the potential difference causes current to flow through the live and the neutral wires
  • the live wire carries the alternating potential from the supply
  • the neutral wire completes the circuit
  • current will only flow in the earth wire if there is a fault connecting it to a non-zero potential
37
Q

A live wire can be dangerous even if a switch in the circuit is open because…..

A

there’s still an alternating current and all it needs is a path for the electricity to flow through

38
Q

Whenever charge flow, it has to overcome the resistance of the circuit. This requires energy, therefore:

A
  • work is done when charge flows
  • the amount of work done depends on the amount of charge that flows and the potential difference
39
Q

What are the two equations for energy transfer?

A

E = power x time

E = charge flow x potential difference

40
Q

how would you carry out the investigating resistance practical?

A

1) set up the circuit
2) attach a length of wire along a metre rule using pieces of tape
3) attach crocodile clip to one end of the ruler and make it align with 0 cm mark on the ruler. then attach another crocodile clip to the length you want to start with
4) record the voltage and current at a range of lengths, using the crocodile clips
5) calculate the resistance
6) repeat steps 4-5

GCSE AQA Physics (16 decks)

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