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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is electric current?

A

The flow of electrical charge

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2
Q

What can be said about the value of current at any point in a single closed loop?

A

Current is the same at all points in a closed loop

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3
Q

What two factors does the current in a circuit depend on?

A

Potential differene (V)
Resistance (R)

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4
Q

What is an Ohmic conductor? State the condition required

A

A conductor for which current and potential difference are directly proportional
Resistance remains constant as current changes
Temperature must be constant

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5
Q

List four components for which resistance is not constant as current changes

A

Lamps
Diodes
Thermistors
Light dependent resistors

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6
Q

What is different about current flow through a diode?

A

The current only flows in one direction
Resistance is very high in the opposite direction, preventing current flow

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7
Q

State what happens to the resistance of a thermistor as temperature increases

A

The thermistor’s resistance decreases

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8
Q

Give two examples of when a thermistor may be used

A

In a thermostat to turn a heater on below a certain temperature
In a freezer to turn on a cooler when the temperature becomes too high

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9
Q

State what happens to the resistance of an LDR as light intensity decreases

A

The LDR’s intensity increases

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10
Q

Give an application for an LDR?

A

Street lights often use LDR’s
When light levels become too low, the light gains sufficient current to turn on

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11
Q

What are the two ways that a component can be connected in a circuit?

A

Series (same loop)
Parallel (adjacent loop)

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12
Q

How does the potential difference across two components vary when connected in series or parallel?

A

Series: Total P.D is shared between each component
Parallel: P.D across each component is the same

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13
Q

If two resistors are connected in parallel, what can be said about their combined total resistance?

A

Their total resistance is less than the smallest of the two individual resistances

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14
Q

If two resistors are connected in series, what can be said about their total resistance?

A

Their total combined resistance is equal to the sum of the two individual resistances

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15
Q

Describe the current in a series circuit

A

In a series circuit, the current is the same at all positions since the charge only has one path to flow through

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16
Q

Describe the current in a parallel circuit

A

In a parallel circuit, the current is shared between the different branches. When the charge reaches a junction it splits

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17
Q

How should you connect an ammeter in a circuit to measure current?

A

Ammeters should be connected in series with the component that they are measuring current through

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18
Q

How should you connect a voltmeter in a circuit to measure potential difference?

A

Voltmeters should be connected in parallel to the component that they are measuring the potential difference of

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19
Q

Is mains electricity an a.c supply or a d.c supply? What do each of these stand for?

A

Mains electricity is an a.c supply
a.c : alternating current
d.c : direct current

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20
Q

Define alternating current

A

Current that continuously changes direction at a specific frequency

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21
Q

Define direct current

A

One directional current flow

22
Q

What is the frequency and voltage of the UK mains electricity supply?

A

Frequency : 50Hz
Voltage : 230V

23
Q

How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires

A

Live wire
Neutral wire
Earth wire

24
Q

State the insulation colour used on the Earth wire

A

Green and yellow stripes

25
Q

State the insulation colour used on the live wire

A

Brown

26
Q

State the insulation colour used on the neutral wire

A

Blue

27
Q

Explain when the Earth wire does and doesn’t carry a current

A

Under normal circumstances, no current flows through the Earth wire
If a fault occurs in the appliance, current will flow to the ground

28
Q

What potential is the neutral wire at?

A

0 volts

29
Q

State the potential difference between the live and earth wires

A

230 volts

30
Q

What is the purpose of the neutral wire?

A

To complete the circuit by connecting the appliance back to the mains supply

31
Q

For metal appliances, where is the Earth wire connected to? Why?

A

Earth wire is connected to the metal casing of the appliance
If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution

32
Q

What two main factors does the amount of energy transferred by an appliance depend on?

A

How long the appliance is being used for
The power of the appliance

33
Q

Describe the energy transfers in a battery powered torch

A

Battery converts chemical energy into electrical energy
Bulb converts electrical energy into light as well as waste energy in the form of heating

34
Q

Describe the energy transfers in a battery powered motor

A

Battery converts chemical energy into electrical energy
Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction

35
Q

What three things determine the power of a circuit device?

A

The potential difference across the circuit
The current through the circuit
The amount of energy transferred in a given time

36
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so that they have access to a source of electricity

37
Q

What are the two types of transformers used in the National grid?

A

Step-up transformers
Step-down transformers

38
Q

Where are step-up transformers found in the National grid? What do they do?

A

Step-up transformers are used when connecting power stations to transmission cables
They increase the potential difference

39
Q

Where are step-down transformers found in the National grid? What do they do?

A

Step-down transformers are used in connecting transmission cables to domestic buildings
They decrease the potential difference

40
Q

Why do transmission lines transfer electricity at high potentials?

A

A high potential results in a low current
The lower the current, the less energy that is wasted as heat
Therefore it is more efficient

41
Q

Why does the potential need to be decreased between transmission lines and houses?

A

Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
Appliances are designed for 230V

42
Q

What can happen when insulating materials are rubbed together?

A

They can become (statically) electrically charged

43
Q

Why can insulators become electrically charged when rubbed together?

A

Electrons are rubbed from one material onto the other
The material gaining electrons becomes negatively charged
The material losing electrons becomes equally positively charged

44
Q

What happens when two electrically charged objects are brought close together?

A

They exert a force onto each other

45
Q

What happens when two identically charged objects are brought close together?

A

They exert a repulsive force on each other and repel

46
Q

What happens when two oppositely charged objects are brought together?

A

They exert an attractive force on each other and attract

47
Q

Give an example of a non-contact force

A

The repulsive or attractive force acting between two electrically charged objects

48
Q

What is an electric field?

A

A region in which a charged object will experience a non-contact electrical force

49
Q

Where can electric fields be found?

A

Surrounding any charged objects

50
Q

Describe the electric field around a charged particle

A

Strongest closest to the object
Decreases in strength as you move away from the object

51
Q

What happens to the force between two charged objects when they are moved closer together?

A

The force between them becomes stronger as the separation reduces

52
Q

In situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?

A

Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials

Physics (8 decks)

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