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Flashcards in P2 Deck (72):
1

What is an electric current?

A flow of electrons

2

Where does an electric current flow ?

From negative end to positive end

3

What do electrons carry?

Energy from the cell. Electrons pass energy to the components in the circuit such as the lamp. In the lamp electrical energy is transferred to thermal and light energy

4

How much energy are electrons carrying then they get to the positive end?

Less energy than when they started

5

What is a conventional current?

Arrow used to show the direction of the current. Scientist always draw the current in the opposite direction

6

What is a series circuit?

Has no branches , current only flows in one path

7

What is the unit of electricity?

Ampere (A) or amp

8

How to measure the current in a circuit?

Used an ammeter

9

What happens to the current when it goes round the circuit?

It is never used up . In a series circuit the current is the same all the way round.

10

What is a parallel circuit?

Contains branches

11

What happens to the current in parallel circuits?

Some current goes through different branches . Current in the branches adds up to the total current leaving the cell.

12

What is the energy transfer in circuits?

-Cells has store of chemical energy
-this is transferred to electrical energy which is carried by electrons passing out the cell
-electrons pass through the components , electrical energy is transferred to other forms of energy
-light energy and thermal in a lamp for examples

13

What is potential difference?

PD of 1 volt tells us that 1 joule of energy is transferred for each coulomb of charge that is moving through the circuit . It basically shows us where the energy is transferred in an electrical current

14

Another name for potential difference?

Voltage

15

How to measure the potential difference?

Voltmeter

16

What happens to the energy carried by a current ?

Shared between components

17

What is the rule with potential difference and parallel circuits?

For components connected in parallel the potential difference across each component is the same .

18

What is a battery?

Two or more cells connected together

19

What is the potential difference of a battery?

The sum of all the cells potential difference

20

What direction do cells have to face for battery to work?

The same direction . A cell in the wrong direction will cancel out one of the cells in the right direction.

21

What is electrical charge measured in?

Coulombs

22

What is a current of 1 ampere equal to?

1 coulomb of charge flowing per second

23

What does the size of an electrical current mean?

Rate of flow of electrical charge

24

How to work out the charge flow?

Q= l x t

Charge flow = current x time

Charge flow , C
Current , A
Time , S

25

What happens as electrons move through a conductor?

Electrons collide with atoms in the metal. Electrical energy is transferred to other forms , eg thermal

26

What is resistance?

The potential difference required to drive a current through a component

27

Equation for resistance?

Resistance = Potential difference / current

Resistance = ohms
PD= V
Current = A

28

What is the job of the resistor?

To add resistance to a current if too much energy for one component.

29

How is the current moving through a resistor and the PD linked?

Directly proportional

30

What cant resistance do?

Change if the current is increased. Resistance is constant

31

What is a way of describing a resistor?

An ohmic conductor

32

What can affect how constant a resistor is?

Temperature

33

Draw current , PD graph for an ohmic conductor

Directly proportional

34

Draw a current , PD graph for a filament lamp?

Heat effects it , not directly proportional

35

What happens when a current goes through a filament lamp?

Not directly proportional as the filament lamp gets hot which causes resistance to increase. As the PD increases , the current no longer increases as much

36

Why does heat effect resistance?

At high temperatures atoms in filament vibrate more. Electrons in the current now collide more with atoms . More energy is needed to push current through the filament .

37

Describe symbol of LED?

Same as diode just with two arrows of the side.

38

Features of diodes?

-current flows in one direction
-diode has very high resistance in reverse direction
-very useful in controlling the flow of current in a circuit.

39

Draw a diodes Pd to current graph?

Stays on the x axis for current in reverse direction. Then lifts up when current is moving forward

40

What is an LED?

Light emitting diode. They give of light when current flows. They are extremely energy efficient source of light

41

Rule for resistors on series circuit?

Add together to get total resistance . The current has to pass through each resistor in turn it cant by pass any resistor.

42

Rule for resistors in parallel?

Total resistance of two resistors in parallel is less that the resistance of the smallest individual resistor

43

Why resistors in parallel have less resistance than the resistance of the smallest resistor?

With 2 resistors in parallel, we have 2 pathways for the current to take . More total current will flow through the circuit

44

What happens if the current has increased but the pd has not changed?

Total resistance has decreased

45

Describe a light dependent resistor symbol?

Symbol of a resistor with a circle around it . Then there are two arrows pointing on to it

46

What are light dependent resistors?

In the dark , LDR has a high resistance . In the light the LDR has a low resistance

47

What are thermistors?

The resistance of a thermistor decreases if the temperature increases.

48

What is power?

Power is the rule at which energy is transferred

49

What is 1 W in terms of joules?

1joule

50

How to calculate the energy transferred in appliances?

Energy = power x time

51

What is a direct current?

A current from a cell , flowing in one direction

52

What electricity does the uk use?

Mains electricity which is an alternating current

53

What is an alternating current?

Current is constantly changing direction

54

Why AC electricity supply is good?

Very easy to use a transformer to increase or decrease the potential difference

55

What is the AC frequency in the uk?

50 hertz

56

What is the AC potential difference in the uk

230 volts

57

What is 1 cycle in mains electricity?

One peak to the next peak

58

What is the national grid?

A system in how electricity is taken from a power station to our homes. It consists of transformers and high voltage cables

59

Why is energy always lost in power cables?

The resistance of the wires . You can reduce this energy lose by building power stations next to homes.

60

How the national grid works ?

1. Electricity passes through the step up transformers with an increase in the PD to several hundred thousand volts
2. Less energy is lost in the power cables when the PD is very high
3. Electricity passes through step down transformers which reduce the pd to 230v.
4. Then it is passed into homes

61

What connects electricity to mains supply ?

Three wires:
-earth
-live
-neutral

62

What are the wires made off?

Copper which is a good conductor of electricity . The coating is plastic , which does not conduct electricity

63

What is the brown wire?

The live wire

64

What is the live wire?

Carries the alternating potential difference from the supply(230v). The live wire is connected to a fuse in the plug

65

What is the blue wire?

Neutral

66

What is the neutral wire?

Completes the circuit , the pd =0 compared to the live wire

67

What is the green yellow striped wire ?

Earth

68

What is the earth wire?

This is a safety wire to stop the appliance from becoming live.

69

Why is the live wire extremely dangerous?

Could be fatal if touched . Even if switch is off, the first part of live wire is still pushing 230v so will still electrocute

70

What happens if somebody touches the live wire?

A current would flow through a person, into the earth , and they'd be electrocuted

71

What is the problem with appliances with metal cases?

If live wire becomes loose the case becomes live. Could be fatal if somebody touches the casee

72

How can appliances prevent the problem of live wires being loose?

Metal case is attached to the earth wire , earth wire is connected to the ground with a metal rod. If the case becomes live, huge current flows to the earth . The fuse melts and stops the current