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Physics > electricity and circuits > Flashcards

electricity and circuits Flashcards

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1
Q

equation for power in terms of forces

A

power = work done/ time

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2
Q

unit for power

A

watt / joule per second

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3
Q

conventional current

A

current that flows from positive to negative

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4
Q

insulator

A

holds the electrons tightly to atoms so the electric currents cannot flow

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5
Q

conductor

A

substances which allow electrons to pass through it

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6
Q

coulomb

A

unit of charge

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7
Q

rules for a series circuit

A
  • the current stays the same
  • has no loops or branches
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8
Q

voltmeter

A

measures the amount of energy per electron

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9
Q

potential difference = …

A

voltage

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10
Q

the bigger the voltage, the bigger the …

A

current

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11
Q

doubling the resistance … the current

A

halves

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12
Q

light dependant resistor

A

(LDR) the resistance decreases as light intensity increases

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13
Q

thermistor

A

resistance decreases as temperature increases

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14
Q

diode

A
  • the resistance of the diode is very high then decreases suddenly at a threshold voltage
  • diodes only let current flow in one direction and only once the voltage has reached a threshold
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15
Q

why can electrons flow more easily through a smaller resistance

A

there are less forceful collisions with the ions in the wire, possibly due to shorter, wider or different metals

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16
Q

uses of diodes

A
  • stops currents from flowing in the wrong direction to prevent damages, e.g. remote batteries
  • diodes can be used to convert alternating current from mains electricity to direct current in a phone charger
17
Q

equation for energy in terms of electric circuits

A

energy = voltage x current x time

18
Q

how to reduce resistance in a circuit

A
  • use low resistance metals such as copper
  • make the wire thicker
  • cool the wire so ions vibrate less
19
Q

calculation for power using resistance

A

P = I^2 x R

20
Q

alternating circuit

A

electricity that is generated when an electromagnet is rotated inside the coil of a machine called an alternator

21
Q

live wire

A

230v connected to generator at power station. can be fatal if touched

22
Q

neutral wire

A

return path of the power station to complete the circuit. should be 0v

23
Q

earth wire

A

connected to the ground with a metal spike for safety. should be 0 volts

24
Q

fuse

A
  • limits the current in the live wire for safety
  • too much current would heat up the wire and may cause fires
25
Q

fault current

A

current that passes through the body

26
Q

earthing

A

connecting the case to the earth to avoid human injury

27
Q

MCB

A
  • miniature circuit breaker
  • disconnects the live wire when the current is too strong
28
Q

what wire is the neutral wire connected to

A

the earth wire at the substation so electric current can feed return via the earth if there is no fault

29
Q

RCD

A
  • remote current decidual
  • switches off electricity automatically if there is a fault
30
Q

equation for charge

A

Q = IT

31
Q

equation for power (electricity)

A

P = E/T

32
Q

equation for energy (electricity)

A

E = QV

33
Q

equation for voltage (resistance)

A

V = IR

34
Q

state the relationship between current in a total circuit and total resistance

A

I=V/R
current is inversely proportional to resistance

35
Q

explain why voltage varies with current in a bulb

A
  • as voltage increases, current increases
  • electrons flow more quickly and collide with metal ions
  • they transfer more energy as they vibrate faster
  • as temperature increases, resistance increases, so voltage increases more rapidly
36
Q

explain how the LDR changes current in a circuit

A
  • resistance decreases as light intensity increases
  • current increases
37
Q

explain why a 20A fuse is not suitable for an 8.7A plug

A
  • realistic fuse amp should be around 13A so it does not melt in normal use
  • 20A is too large, would not protect the cable as the cable would over heat and start a fire before the 20A fuse melts and cuts of the current
38
Q

explain how the fuse works with the earth wire to prevent the user from being electrocuted

A
  • if live wire touches metal casing, a large current would flow through the person to earth, causing electrocution
  • if casing is earthed, a large current would flow from the live wire via the case to earth
  • the fault current would blow a fuse in the live wire, disconnecting it, making it safe
39
Q

on which wire, (earth, live, neutral), should the switch be connected to

A
  • the live wire
  • when switched off, the kettle has no high voltage and is safe

Physics (11 decks)

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