Physics topic two

What is static electricity?

The build up of charge on insulating materials

How does static electricity cause a spark?

When discharged

What does it mean for static electricity to be discharged?

A sudden release and movement of built up electrons from a charged objects to another charged object or the ground

What causes static electricity?

When two insulating materials are rubbed together, the friction causes the electrons to be transferred from one material to another.

the material that losses the electrons become positively charged and the material that gains the electrons become negatively charged.

Why doesn't static electricity usually occur in conducting materials?

The electrons are able to move , the electrons flow back to the material therefore no charge builds up

Describes what happens when a polythene rod is rubbed against a material?

Gains electrons

Describe what happens when a acetate rod is rubbed against a substance?

Looses electrons

Describe the process in which static electricity can create a spark?

If the size of the charge increases , a PD develops , if the PD is large enough electrons can transfer across a gap creating a spark.

Give an example of static electricity occurring on a conductor?

Can occur on a cars metal frame

Describe the process in which air is able to conduct electricity?

A strong electric field can cause air particles to loose electrons creating positive ions - this process is called ionisation

What is a circuit?

A closed loop with a power source and something for the electrons to flow through

What is current?

The rate of the flow of charge

What is potential difference?

Energy transferred per unit charge passed

What is resistance?

Anything that opposes the flow of electric current

What is the type of current used in the exam?

Conventional current

What is conventional current?

The flow of charge from positive to negative

What is the direction of electron flow?

from negative to positive

What is the charge of the long side of the cell diagram?

Positive

What is the charge of the short side of the cell diagram?

Negative

What is charge?

A property of matter

What is the unit of charge?

Coulombs, C

What is the equation that links charge, time and current? L

Charge = current x time

What are parallel circuits?

Circuits that have more than one path for electron flow though.

Describe the potential difference in a parallel circuit

Same throughout all components

Describe the current in a parallel circuit

shared between components

Describe the resistance in a parallel circuit

The total resistance of a parallel circuit is less than the resistance of the smallest individual resistor.

Adding more components in parallel decreases the overall resistance because it provides extra pathways for the current to flow.

what is a series ciruit?

A circuit that has a single loop

Describe the PD in a series circuit

The total p.d. is shared between each of the components

Describe the current in a series circuit.

It is the same through each component.

Describe resistance in a series circuit

The total resistance is equal to the sum of all the resistance across the components when current is constant

RT = R1 + R2 + R3....

in a series circuit greater resistance = greater...

Voltage

what is the equation that links voltage, resistance and current?

V = IR

Describe the resistance in a fixed resistor.

As long as the temperature and resistance remain constant, the current is directly proportional to the voltage.

(If voltage doubles, current doubles).

Describe the resistance in a filament lamp

the resistance increases as the temperature of the filament increases.

Describe the resistance in diodes

the resistance is very high in one direction but very low in the opposite direction.

What is AC?

Alternate current

A current that continuously changes its direction, going back and forth around a cirucit.

What causes alternate current?

an alternating potential difference

What is DC?

Direct current

A current that is constantly flowing in the same direction in a circuit from positive to negative

What is the frequency of an alternating current?

The number of times the current changes direction back and forth each second

This is 50Hz

What type of current in the UK mains?

An alternating current

Has a frequency of 50HZ and a PD of 230V

Describe the terminal in an alternating current

Two identical terminals that constantly swap polarity

Describe the terminals in direct current

has a fixed positive and fixed negative terminal

What produces Direct current?

Cells and batteries

What produces alternating current?

Electrical generators, such as mains electricity.

What is meant by a terminal

The connection points on a power source where current enters or leaves a circuit.

What do we use to produce graphs that showcase A.C and D.C?

An oscilloscope

What is a are the positives and negatives of using a series circuit?

+++++++

# Cheap and easy to wire

# One switch controls all components at once

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# A single break prevents the whole circuit from working

# Cannot turn off or on components separately

# Adding more items increases resistance and lowers the current

What is a are the positives and negatives of using a parallel circuit ?

+++++++++

# Each component can be switched on or off separately.

# A break in one loop does not stop the other loops.

# Every component gets the full supply voltage, so lamps stay bright.

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# Complex wiring

# Adding loops lowers total resistance, drawing more current from the source.

# Higher overall current empties the power supply more quickly

What do cells and batteries do?

Provide electrical power to a circuit

What do switches do?

Control the flow of electricity

What do fuses do?

Break if there is too much current

What do fuses prevent?

- Overheating

- Electrical fires

- Electric shock

- Component damage

What does LED stand for?

Light Emitting Diode

What do diodes do?

Only allow current to flow in one direction only

What do LEDs do?

emits light when current flows through

What do ammeters do?

Measure current

What do voltmeters do?

Measure voltage/ Potential difference

How must voltmeters be connected?

In parallel

What do fixed resistors do?

Provides a fixed amount of resistance to a circuit

What is a variable resistor?

A resistor that allows the user to easily modify the resistance provided

What does LDR stand for?

Light Dependent Resistor

What are LDRs

Resistors in which resistance depends on the intensity of light

Describe how LDRs can be used in burgler alarms

If someone switches on a light, this will lead the resistance to decrease, allowing current to flow, enabling an alarm to ring.

Describe how light affects resistance in LDRs

The darker the environment the more resistance.

What are thermistors?

Temperature dependent resistors. As the temperature increases the resistance decreases, as a result more current flows through.

What is the national grid?

Network of transformers and wires that spread across the country to distribute electricity

Where is most of the UKs energy generated?

Power Stations

How do power stations produce energy? And what type of energy may this relate to?

Chemical/Nuclear energy to Thermal: Fossil fuels are burned (or nuclear fission occurs) to heat water and turn it into high-pressure steam.

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Thermal energy to Kinetic energy : The rushing steam drives a turbine, making it spin.

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Kinetic energy to Electrical energy : The spinning turbine turns a generator, which generates an electric current by electromagnetic induction.

What does the quantity of energy produced by a powerstation dependent on?

The demand

When does demand for electrcity increase?

Afternoon and the evening

What do powerstions do to cope with the surges in demand of electricity during peak times?

They run below their maximum capacity as if they do run at their maximum capacity, they cannot provide the extra electricity needed

What is power

The rate in which energy is transferred

Why does the voltage need to be inecreased when being transmitted across the national grid?

increasing the PD lowers the current, minimising the amount of energy wasted as heat due which is produced due to the resistance of the wire

Describe the process of electricity moving via the national grid

power station ----> step up transformer -----> high voltage transmission lines connected to pylons -----> step down transformer

Describe how voltage changes through the national grid.

leaves powerstation at 25,000v ----.>

step up transformer increases voltage ti 400,000V -----> step down transformer decreases voltage to 230V making it safe to use

Why must voltage be decreased by step down transformars?

~ A high voltage is dangerous

~ A high voltage could damage appliances

What are surges?

Sudden increase in current

What causes surges to occur?

- Turning appliances on or off

-A fault in the circuit or appliance

Why are surges dangerous?

- They can damage the appliance

- They can cause fires

- They can lead to electric shocks

How do fuses work?

Fuses are a very thin piece of wire

A surge will cause that wire to melt and therefore break the circuit meaning no more current can flow through

How can fuses be used effectively?

The fuse needs to have a larger amp rating than the current appliance

What are the positives and negative of using fuses?

+++++

# Simple to use

# Cheap

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# Permanently broken after a surge

How do circuit breakers work?

They get tripped when there is a surge

This turns off the circuit

This effect can be reset

what are the positives and negatives of circuit breakers

+++++

- The effects can be reset

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- More expensive

Why is earthing required

Surges can causes harm by making the live wire loose

This may touch the casing

If a person touches the casing they will get electrocuted

Earthing prevents this

How does earthing prevent electrocution?

The earth wire acts as an alternative pathway meaning electricity is diverted through the earth wire towards the earth

What is double insulation?

This is when the entire alplience is covered in plastic which is an insulator

Meaning there are no exposed metal parts that can be touched

No earth wire is required

What are two way that electrocution can be prevented when it come to appliances

Double insulation

Earthing (introducing an earth wire to the plug)

What is mains supply?

Electricity supplied by the national grid

It is an AC at 230V and is at 50Hz

How many wires are there in a UK plug?

3

What are the wires in a Uk plug made of and coated in?

Made of copper

Coated in plastic

What is the brown wire and what does it do?

Live wire

provides an alternating P.D(230V) from the mains supply

What is the blue wire? What does it do?

The neutral wire

It completes the circuit by carrying away current

How does the neutral wire complete the circuit?

Provides a physical return path back to the power stations or local substation

How does electricity flow through the plug when there are no faults in the wiring?

Flows into the appliance via the live wire and out via the neutral wire

What is the striped yellow and green wire? What does it do?

Earth wire

Prevents the appliance casing from becoming live by providing an alternative pathway for the current to flow away

What potential difference is the earth and neutral wire?

0V

A main switch connects a household appliance to the mains electricity supply. Explain why a person could still receive a dangerous electric shock if they touch the live wire inside the appliance, even when the appliance is switched off.

the live wire is still at a high PD of 230V

The person touching it has a PD of 0V, touching the wire creates a large PD across their body, causing the current to flow through them towards the ground.

Why don't we use a copper wire in the resistance of a wire practical?

The resistance would be too low to measure easily

What wire do we use in the resistance of a wire practical? Why?

Nycrome

It has a high resistance, making the resistance easier to measure