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Flashcards in Electricity Deck (66):
1

What is current?

The rate of flow of an electrical charge

2

When will current flow?

When the circuit is complete as a potential difference is needed

3

What is current measured in

Amps

4

Is there change in current in a closed circuit?

No the current stays the same everywhere in the circuit

5

What is potential difference?

It is a force that pushes the charge around

6

What is Potential difference measured in?

Volts

7

What is resistance?

The opposite of potential difference it slows the rate of flow of charge

8

What is resistance measure in

Ohms

9

What affects the amount of current flowing through a component?

The potential difference across the circuit and the resistance of the component

10

Define the relationship for the amount current between potential difference and resistance

The greater the resistance across the component, the smaller the current that flows (for a given potential difference across the component)

11

What is the equation for charge flow past a particular point in a circuit

Charge flow (coulombs, C)=Current(A) x Time (S)

12

What is the formula linking potential difference, current and resistance?

V=IR
potential difference=current x resistance

13

How could you investigate factors that effect resistance FOR EXAMPLE LENGTH?

attach crocodile clip to the wire where the length is at 0cm on the ruler

then write down the distance you place the second crocodile clip on the ruler and place it

close the switch and record the PD and current for that length

then open the switch replace the 2nd CC and close the switch again and record PD and current

you can then use v=ir to get the resistance for the wires

then you can plot a graph for length against resistance

should be proportional and going up

14

What does a voltmeter do?

It measures the potential difference across a wire

MUST BE PLACED IN PARALLEL AROUND WHATEVER YOUR INVESTIGATING

15

What does an resistor always have at a constant temperture

a constant resistance within a circuit
so current is directly proportional to PD

16

What resistors do change with change in current?

diodes and filament lamps or bulbs

17

Why does a bulb change its resistance?

as current flows through the lamp the current also has to increase so the hotter the lamp gets the higher the resistance

18

Why does a bulb change its resistance?

as current flows through the lamp the current also has to increase so the hotter the lamp gets the higher the resistance as the hotter something is the higher the resistance

19

Why does a diode change its resistance?

The resistance depends on the direction of the current. They will happily let current flow in one direction, but have a very high resistance if it is reversed

20

How would you find out a components IV characteristics?

get a battery an ammeter and a voltmeter, and variable resistor and the component your investigating set up in a circuit

vary the resistors resistance which alters the current flowing through the circuit and the PD across the component

take several pairs of reading from the ammeter and the voltmeter to see how PD changes along with C. repeat each reading twice and take an average of both readings

then swap over the wires so that the current is reversed

then plot graphs using readings (current against voltage)

21

What should and ohmic conductor/ resistor IV graph look like

They should be directly proportional

22

What should a filament lamp/bulb IV graph look like?

it should curve up at the bottom and level off at the top

23

What should a diodes IV graph look like?

It should stay level then curve upward suddenly

24

What is a LDR?

It is a light dependent resistor
in bright light the resistance lowers
in dark the resistance goes higher
used in burglar alarms, night lights and outdoor lighting

25

What is a thermistor?

It is a resistor that changes resistance depending on temperature
in hot conditions the resistance drops
in cold the resistance gets higher
used in temperature detectors car engine temperature sensors and in electronic thermostats

26

Where can LDR'S and thermistors also be use?

in sensing circuits!!
the fixed resistor and fan will have the same pd across them as they are connected in parallel
the pd from the power supply is shared out between the thermistor and the loop
as the temperature rises the resistance of the thermistor decreases meaning more pd can be given to the fan and the resistor making the fan spin faster
(same with an LDR)(you can reverse the effect by moving the resistor and the adjustable resistor)

27

What is a series circuit?

The circuit is all connected in a singular closed circuit where the current only flows along one wire with components one after another

28

What happens if you disconnect a component in a series circuit or if one fails?

The flow of current will stop and the circuit will not be able to carry charge

29

What is the PD rule in a series circuit?

The PD is shared between components, so the components PD adds up to the total PD

30

Give the equation for PD

total PD= PD1 + PD2 +....

31

What is the rule for current in a series circuit?

The same current flows through all the components, so the current is the same everywhere.

32

What is the equation for current in a series circuit?

current1=current2=current3=current4

33

What equation determines the current in a series circuit?

I= V/R

34

What is the rule for resistance in a series circuit and why?

The resistance adds up, as adding a resistor in series the resistors have to share the total PD and resistance is the opposite of PD

35

Why does adding a resistor in a series circuit reduce current?

It lessens the PD (as is opposite of it) going across each component which means less current is being pushed around, and as the rule for a series circuit is that current is the same everywhere the total current in the series circuit is reduced

36

What is the rule for cells in a series circuit?

The cell PD's add up, if theyre all connected the same way,

37

What is a parallel circuit?

It is when each component is seperatley connected to the positive and negative of the supply

38

What advantage is there to having a parallel circuit?

If a component is removed or disconnected it will hardly effect the rest of the circuit

39

What is the rule for PD in a parallel circuit?

The PD is the same across all the components

So identical bulbs connected in parallel will have the same brightness

40

What is the rule for current in a parallel circuit?and equation

Current is shared between branches of the components
if two components in parallel are connected the current will flow the same through each component
currenttotal=current1+current2+...

41

What happens if you add a resistor in a parallel circuit?why

if two or more resistors are connected in parallel
it reduces total resistance
as both resistors have same PD in parallel
so pushing force is the same as the source pd for each resistor that you add
by adding another loop current has more than one direction to go in
This increases the total current around the circuit
so in parallel an increase in current means a decrease in total resistance

42

How can you investigate resistance in a series circuit?

get two or more identical resistors

build a circuit using one of the resistors and a battery and a ammeter(take note of the PD of the battery)

measure the current going through the ammeter and calculate the resistance of the first resistor use R=V/I

Then add the other resistor in series with the first

Measure the current again and use the pd of the battery to find the total resistance

repeat these steps with all the resistors and then plot a graph with number of resistors against total resistance

43

How could you investigate resistance in a parallel circuit?

If done after test for series use same equipment for fair test but if not get a number of identical resistors, ammeter and a battery (note PD) and build the same initial circuit and measure the resistance using R=V/I

set up the circuit so the resistor is in parallel with the other

then measure the current and the PD and use equation to get resistanc

repeat steps until all resistors are measured in parallel

plot a graph with number of resistors against total resistance

44

What should happen when you add resistors in series

increases the resistance, and the more you add the more resistance there is. Directly proportional

45

What should happen when you add resistors in parallel

The total current through the circuit increases so the total current decreases. The more resistors you add the smaller the total resistance. graph should curve

46

What is alternating current (ac)

Current is constantly changing direction. Produced by alternating voltages where the positive and negative ends keep alternating.

47

What kind of power is in your home? and at what voltage?

230volts and its AC

48

What is direct current (DC)

Current is always flowing in the same direction and created by a direct voltage (that's why batteries are never ac)

49

What colour is the live wire in a plug? and what does is do?

Brown
provides the AC PD of 230v from the mains supply

50

What colour wire is the neutral wire in a plug? and what does this do?

Blue
It completes the circuit and carries away current - electricity normally flows in the live wire and out the neutral wire with a 0v

51

What colour is the earth wire in a plug? and what does this do?

green and yellow
protecting the wiring against the appliance so that if the wire hits a conductive surface on the appliance it will not shock you. At 0v

52

What happens if yo touch the live wire or the earth wire when there is a fault?

It will shock you as there is a large PD of 230v in the wire and 0v in you
Still danger even if a switch is off as there is still a live wire that can never turn off unless so at the fuse box

53

What are electrical appliances designed to do

transfer energy to components when a current flows

54

The more current the....

more energy is transferred thermally

55

What is the equation for energy transfer?

Power (w) x TIme (s)

E(J)=Pt

56

What does the power rating on an appliance tell you?

the amount of energy transfer per second

57

What happens when an electrical charge goes through a change in PD?

Energy is transferred

Energy is supplied to the charge at the power sourceto raise it through potential

Charge gives up its energy when it falls through and potential drop in components

58

What is the equation for PD when energy is transferred?

E(j)=Q(c) x V(v)

charge flow x potential difference

59

The more PD the more...

energy will be supplied to the circuit for every coulomb of charge as it is raised higher at the start

60

what is th eequation for power involvining PD and a current

Power(w)=PD(V) x Current(A)

P=VI

or P=I^2R

61

What is the national grid?

a system of cables and transformers that cover the UK and connects power stations to the consumers

transfers electricity from a power station to wherever it is needed

62

How does power out put on the grid change

more used in mornings and evenings
more used when cold or dark
more when popular events happen on TV
power stations have headroom for these increases and small stations on standby just incase

63

How is large amount of power transmitted

high Pd or high Current

64

Why is high current a problem

power is lost as wires heat up and energy is lost to thermal store

65

How does NG transmit power

high pd low current

66

How is the PD and current changed before transmition on NG?

goes through a step up transformer goes across pylons then another step down transformer then to the consumer