Additional Science P2.3 Electricity

P2.3 Electricity

P2.3 Currents in electrical circuits 

The current in an electric circuit depends on the resistance of the components and the supply. You should be able to: ■ apply the principles of basic electrical circuits to practical situations ■ evaluate the use of different forms of lighting, in terms of cost and energy efficiency.

P2.3.1 Static electricity 

Static electricityElectronsRepelAttractElectric charge

P2.3.1 Static electricity 

a) When certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and onto the other.

b) The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.

c) When two electrically charged objects are brought together they exert a force on each other. d) Two objects that carry the same type of charge repel. Two objects that carry different types of charge attract. 

e) Electrical charges can move easily through some substances, eg metals. The flow of electric charges is called current electricity.

Key wordsCurrentResistanceComponentsEnergy efficiencyStatic electricityElectronsRepelAttractElectric chargePotential differenceVoltageWork doneEnergy transferredCoulombSwitch

LampFuseAmmeterResistorThermistorVariable resistorLDRLEDResistanceFilament bulbDiodeCellsBatteriesEarthLive wireNeutral wireElectrical chargeResistor

P2.3 Electrical circuits:Series and parallel

circuits

CurrentResistanceComponentsPotential differenceVoltageCoulombSwitch

LampFuseAmmeterResistorResistanceCellsBatteries

http://www.teachitscience.co.uk/shared/free/CircuitBuilder_iframe.html

Key words

Circuit symbols

CURRENT ISSUESA battery is connected to a bulb. The bulb is glowing.

Which of the four diagrams A - D in your opinion best describes the electric current in the wires?

A. There will be no electric current The electric current will be in a in the wire attached to the base direction towards the bulb inof the battery. both wires.

The direction of the current will The direction of the electric currentbe as shown. The current will will be as shown. The current willbe less in the return wire be the same in both wires.

Give a reason for your answer:

http://www.teachitscience.co.uk/shared/free/CircuitBuilder_iframe.html

R1 R2

Resistance matters

A battery is connected to a bulb and two variable resistors, as above. The bulb is glowing

What happens to the bulb if ….

R1 increase/ decrease?

R2 increase/ decrease?

I is the current in amperes (A)Q is the charge in coulombs (C)t is the time in seconds (s)

a) Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric charge. The size of the current is given by the equation:

A coulomb is 6.2 x 1018 electrons. As the electrons flow around the circuit they do not get used up.An amp is a 1 Coulomb per second.

b) The potential difference (voltage) between two points in an electric circuit is the work done (energy transferred) per coulomb of charge that passes between the points

V is the potential difference in volts (V)W is the work done (energy transferred) in joules (J)Q is the charge in coulombs (C)

A battery is a number of cells joined together. They supply energy to each coulomb as they flow around the circuit. The energy is transferred from the battery (chemical potential energy) to the components in the circuit eg a lamp (light and heat energy). Batteries are measured in volts. Voltage is the push given to the electrons as they flow, it is often called potential difference (pd). A volt is a joule per Coulomb.

Voltage (V)(or potential difference) is how much energy the charge is given by the power supply.

Voltage = PUSH

Current (A) is how much charge flows in the circuit in a certain time.

Current = FLOW

Resistance (Ω) is how hard it is for the current to flow

Resistance = TRYING TO STOP

What are these?

What job does each one do in a circuit?

BTEOTSSSBAT:

Identify series circuitsIdentify parallel circuitsInvestigate how current flows through series and parallel circuitsInvestigate how voltage flows through series and parallel circuits

What do we use to measure a current?

What do we use to measure a potential difference (voltage) across a component?

ammeter

voltmeter

digital multimeter

Series circuits

What happens to the current as more components are added?

Series circuits

What happens to the voltage as more components are added?

Series circuit

CURRENT:The current is always the same at each point in the circuit.

VOLTAGE:The voltage differs over each component - but the total over each component will add up to the total provided by the battery

Parallel circuits

What happens to the current as more branches are added?

Parallel circuits

What happens to the voltage as more branches are added?

Series circuit

CURRENT:The current is always the same at each point in the circuit.

VOLTAGE:The voltage differs over each component - but the total over each component will add up to the total provided by the battery

Parallel circuit

CURRENTIt splits up - but current in = current out

VOLTAGEIs the same over each parallel component. It is the same as the voltage of the battery.

Extension:Series and parallel circuits

BTEOTSSSBAT:

Know the relationship between current, voltage and resistanceSolve problems using Ohm's lawIdentify electrical safety problemsWire a three-pin plug correctly

What are the variables?IndependentDependentControlled

What are the main sources of error?

How can it be minimised?

What is the main health and safety issue?

How can it be minimised?

Match the brightness of the bulbsWhich is the brightest?Which is the dimmest?

1. What current will flow through a 20Ω resistor with a voltage of 6V across it?

V = 6V R = 20Ω

so C = V/R = 6/20 = 0.3A

2. What voltage is needed to make 0.5A flow through a 100Ω resistor?

3. A current of 0.23A flows through a bulb when a voltage of 20V is across it. What is its resistance?

What components would produce these graphs?

What voltage would you get from these combinations?

True or false?

The current through each resistor is the same

The voltage across each resistor is the same

The total resistance is 150Ω

Calculate the current through each resistor

How are these 2 resistors arranged?

True or false?

The current through each resistor is the same

The voltage across each resistor is the same

The total resistance is 150Ω

How are these 2 resistors arranged?

What will the voltage be across each resistor?

This is an LDR. Its resistance gets …………….. when light falls on it.

This is a ……………….

Its resistance depends on which way round it is connected

This is a thermistor. Its resistance gets bigger when it gets …………….

This is a filament lamp. Its resistance gets bigger when it gets ……………..

1. How much heat energy does a 3kW kettle produce in 2 minutes?

P = 3,000W t = 120s

So E.T. = P x t = 3,600,000J

2. An electric fire produces 500,000J of heat energy in 3 minutes. Calculate its power.

3. How long will it take a 2kW water heater to give 300,000J of heat energy to the water inside it?

1. A current of 0.5A flows through a 240V bulb. Calculate its power.

C = 0.5A V = 240V

P = V x C = 240 x 0.5 = 120W

2. What current flows through a 60W, 240V bedside lamp?

3. Which of these fuses should be used inside its plug?

1A 5A 10A 15A 30A

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