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A - Physics GCSE > Topic 5 - Electricity and Circuits > Flashcards

Topic 5 - Electricity and Circuits Flashcards

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1
Q

How do you measure voltage

A

current x resistance

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2
Q

What is meant by potential difference

A

driving force which pushes the charge around

higher the PT the higher the current

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3
Q

How do you measure current

A

Potential difference / resistance

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4
Q

What is the current

A

Flow of electric charge (electrons) around a circuit and it will only flow if theres a potential difference

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5
Q

What is resistance

A

anything that slows the flow down

usually increases with temperature

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6
Q

How do you measure charge

A

current x time

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7
Q

What is charge

A

current is the rate of flow of charge.

its a flow of electrons

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8
Q

Describe the current and potential difference in a series circuit

A

Current is the same everywhere

PT is shared between each component

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9
Q

How does the Resistance change in a series in you add a resistor

A

It increases

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10
Q

Describe the current and potential difference in a Parallel circuit

A

Current is shared at junctions/branches

potential difference is the same across all components

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11
Q

Why does resistance increase with temperature

A

because the electrical charge has to do work against the resistance
as the current flows through a resister it heats up because the electrons are colliding with ions in the lattice resistor
-If resistor too hot no current will flow (unless thermistor)

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12
Q

How could you investigate a component in series

A

-connect a voltmeter in parallel with the component you’re investigating and ammeter in series
-change the potential difference on power supply and take several readings from the ammeter and voltmeter
for different output voltages
-Plot I-V graph to work out resistance
(make sure circuit doesnt overheat)

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13
Q

What would you find if you swapped the direction of a diode

A

current cant flow through anymore

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14
Q

What would you find if you kept the PT of a thermistor the same but gradually increased the temperature

A

that as the temperature increases the current through the resistor decreases and the resistance decreases

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15
Q

Describe a test for a LDR

A

Carry out in dim room

  • keep PT constant but slowly adjust the light level near the LDR and measure the current through LDR
  • should find as light intensity increases, current increases and resistance decreases
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16
Q

Describe an IV graph for Resistors and wire

A

current is directly proportional to PD so straight line

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17
Q

Describe an IV graph for a Filament lamp

A

Increasing current increases temp which makes resistance increase so theyre curved

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18
Q

Describe an IV graph for a diode

A

current only flows through a diode in one direction
diodes have high resistance in opposite direction
(so flat line and then sudden increase)

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19
Q

What is an LDR and name some uses

A

Light dependent resistors

  • in bright light resistance falls so current increases
  • used for automatic night light lights and burgler detectors
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20
Q

What is a thermistor and what is it used for

A

hot conditions resistance drops
-used in temperature detectors eg) electric kettles
car engines

21
Q

How does resistance change in a series and parallel when you add a resistor

A

Series- increases resistance- makes resistors have to share PD

Parallel - decreases total resistance as both resistors have same PD and by adding another loop for resistor you are giving the current another direction so increase in current= decrease in resistance

22
Q

How can we find the energy transferred in a system with a formula?

A

Current x Potential Difference x time

23
Q

Explain why the transfer of energy leads to heating

A

Because as energy is transferred some is as thermal energy to thermal stores as heating usually increases resistance. so its dissipated to surroundings

24
Q

How is efficiency effected by heating

A

it decreases

25
Q

what can happen to components in a circuit if the temperature increases too high

A

It can cause them to melt and stop working properly

26
Q

how do fuses help protect circuits from overheating

A

they melt and break the circuit if it gets too high

27
Q

Why can a heating effect be useful

A

it toaster a coil of wire has a very high resistance so gives off infrared radiation to bread and cooks it

28
Q

How do you work out Power in a circuit

A

Energy transferred / time

29
Q

What is power

A

The rate it transfers energy per second

30
Q

What does a power rating show

A

the maximum safe power an appliance can opperate at

shows the max. energy transferred between store each second

31
Q

How can you work out electrical power with Potential difference

A

Current x PT

32
Q

How do you work out Power with Resistance

A

Current^2 x resistance

33
Q

A mains supply has a……..current

A

an alternating current

34
Q

A battery supply has a…….current

A

direct current

35
Q

What is the potential diffence of UK mains power supply

A

230V

36
Q

What is the frequency of the UK Mains power supply

A

50Hz

37
Q

How can you turn A.C to D.C

A

using a diode

38
Q

Describe the neutral wire

A

blue-
completes the circuit
electricity flows out of this wire
has PT of 0Volts

39
Q

Describe the Live wire

A

brown- carries the Potential difference/voltage

alternates between high positive and negative voltage of 230V

40
Q

Describe the Earth wire

A

Green and Yellow
it has a PT of 0volts
used for safety and protecting wires
it carries current away to earth if something goes wrong

41
Q

What is a double insulated appliance

A

doesnt have an earth wire as its already earthed

42
Q

Why does touching a live wire give you an electric shock

A

Your body is at 0 volts like an earth wire so if you touch a live wire a potential difference is produced across your body and a current flows through you

43
Q

How could a fire start in a circuit

A

-any connection between a live and neutral wire is dangerous as it creates a low resistance path to earth and huge current so fire could start

44
Q

What do fuses and earthing do

A

Prevent electrical overloads which could start a fire or melt you components or give deadly electric shocks

45
Q

How does a fuse work

A

if a fault develops in live wire, then the current flows through the case and down the earth wire

  • this surge melts the fuse when current exceeds rating and breaks circuit stopping live supply
  • it isolates the whole appliance so you cant get shock
46
Q

What should a fuse rating be

A

near as possible but just higher than the normal operating current

47
Q

The larger the current the ……the cable needed to carry it

A

thicker

48
Q

What is circuit breaker

some pros and cons too

A

instead of a fuse a circuit breaker trips the circuit so it turns off quicker than the time a fuse would melt
+they can be reset so dont need replacing as much
- but are more expensive

49
Q

What does double insulating materials mean

A

a plastic casing (instead of metal) has no metal parts showing so doesnt need an earth wire

A - Physics GCSE (9 decks)

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