electricity and circuits Flashcards

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
fault current
current that passes through the body
26
earthing
connecting the case to the earth to avoid human injury
27
MCB
- miniature circuit breaker - disconnects the live wire when the current is too strong
28
what wire is the neutral wire connected to
the earth wire at the substation so electric current can feed return via the earth if there is no fault
29
RCD
- remote current decidual - switches off electricity automatically if there is a fault
30
equation for charge
Q = IT
31
equation for power (electricity)
P = E/T
32
equation for energy (electricity)
E = QV
33
equation for voltage (resistance)
V = IR
34
state the relationship between current in a total circuit and total resistance
I=V/R current is inversely proportional to resistance
35
explain why voltage varies with current in a bulb
- 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
explain how the LDR changes current in a circuit
- resistance decreases as light intensity increases - current increases
37
explain why a 20A fuse is not suitable for an 8.7A plug
- 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
explain how the fuse works with the earth wire to prevent the user from being electrocuted
- 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
on which wire, (earth, live, neutral), should the switch be connected to
- the live wire - when switched off, the kettle has no high voltage and is safe