Electricity EnergyCH 6.1, 6.2, 6.3 AND 6.4 STARTING AT PAGE 183

Teacher Resources - S:\Science\7-12 wikis

Introduction Video on Electricity - BBC Bitesize

Overview of Electricity - BBC Bitesize

Ch 6.1 Electricity - quizlet

Electric circuit symbols - quizlet

Ch 6.2 Measuring electricity - quizlet

Ch 6.3 Practical circuits - quizlet

Ch 6.4 Electromagnets, motors and generators - quizlet

Cool UK - electromagnetism and motors

BBC Bitesize - Overview of Electromagnetism

BBC Bitesize - Video - motors and electromagnetism

Ch 6.1 Simple circuits

Electrical Charge

Protons are positive

Neutrons are neutral

Electrons are negative

Static electricity

Statistic electricity – the build up of electrons on a surface. Usually due to one surfaces rubbing against another surface.

Electrons are removed from one surface (becomes positive) and

Electrons are added to the other surface (becomes negative)

This charge may leak slowly into the surrounding atmosphere, or

The electrons may jump across a gap and discharge in one go, releasing light, heat, sound and kinetic energy – a spark.

Lightning is the build up of static charge in the atmosphere that then jumps to the earth, a building or another cloud.

Static Electricity - Interactive page 184

Current electricity

Current electricity is made up of a continuous and uninterrupted flow of electrons

The moving electrons have energy that can be converted into other forms of energy – eg light, heat, sound, magnetism

A circuit usually requires the following components: power source, wires to connect all elements of the circuit, an energy user (light, buzzer, amplifier, element etc) and a switch.

Each component has specific symbol to represent it in diagrams

Current Electricity – Videos page 185

Circuit components symbolsCircuit components memory game - Interactive page 185

Circuit diagram

Circuit diagrams

Torch circuit diagrams

Series & parallel circuits

There are two types of circuit we can make, called series and parallel.

The components in a circuit are joined by wires.

if there are no branches then it's a series circuit

if there are branches it's a parallel circuit

Series circuits

In a television series, you get several episodes, one after the other. A series circuit is similar. You get several components one after the other.

If you follow the circuit diagram from one side of the cell to the other, you should pass through all the different components, one after the other, without any branches.

Parallel circuits

In parallel circuits different components are connected on different branches of the wire. If you follow the circuit diagram from one side of the cell to the other, you can only pass through all the different components if you follow all the branches. Blue

Review Questions p 186

1 Charges of:

a an atom = neutral (0)

b a proton = positive (+)

c a neutron = neutral (0)

d an electron = negative (–).

2 a In an atom, the number of protons = the number of electrons.

b In a positive ion, the number of protons > the number of electrons.

c In a negative ion, the number of protons < the number of electrons.

3 When a spark jumps across a gap, energy is released as light, and some is released as light and heat (and perhaps sound).

5 Electrons are the charged particles that carry an electric current through a circuit.

An electric circuit needs: an energy source

an energy converter

wires.

A circuit usually has a switch too, although this is not essential.

6 Examples of:

a an energy supplier: battery, generator, dynamo

b components that use electrical energy: light globe, heating element, motor.

Ch 6 Review Ans.docx

Ch 6.2 Measuring amps & volts

Current

Current is a measure of how much electric charge flows through a circuit. The more charge that flows, the bigger the current.

Current is measured in units called amps. The symbol for amps is A. For example, 20A is a bigger current than 5A.

Measuring current

A device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but most have a digital readout. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.

Ammeters are placed in series

Voltage

Voltage

Voltage is a measure of the difference in electrical energy between two parts of a circuit. The bigger the difference in energy, the bigger the voltage.

Voltage is measured in volts. The symbol for volts is V. For example, 230V is a bigger voltage than 12V.

Measuring voltage

Voltage is measured using a voltmeter. Some types of voltmeter have a pointer on a dial, but most have a digital readout. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it.

Practical measurement in circuits

1. Go to S:\Science\7-12 wikis and open up the circuit construction app and the ‘Measuring Current in series and parallel circuits PhET - Ohm's Law Mr Wust’ document. You have 2 minutes to complete the tasks.

2. Open ‘Ch 6 Worksheet 1 Circuit Calcs’ from S drive and complete the calculations. This is available for download from the Pearson text book on page 190

3. Page 182 Interactive Electrical Terms matching items.

Ch 6.2 Wet cells, dry cells and photovoltaic cells

Wet cell - 2 different metal electrodes and an electrolyte solution eg car battery - acid and metal electrodes

Dry cell - contain a conducting paste, and electrodes - doesn't leak

Photovoltaic Cell - contain semi-conducting silicon crystals - sunlight knocks electrons off the crystal and they are used to create a current.

Resistance V = IR

As electrons pass along a wire, their progress is restricted by the atoms they encounter. Energy is lost as heat or light. Too much resistance and the wire will melt creating a fire.

Factors affecting Electrical Resistance

1 - type of material - metals provide little resistance. 2 - as the length of the wire increases, then so does the resistance. 3 - as the diameter of the wire increases, the resistance decreases.

Conductors and insulators

Conductors

Metals are conductors - they offer very little resistance. Copper and Aluminium are the better ones – graphite (carbon).

Insulators

Have such a high resistance, that no current is possible - rubber, plastics, wood glass and ceramics.

Ch 6.3 Practical Circuits

Series Circuit

all of the components are in a single simple loop or circuit - if a globe burns out the circuit fails. Adding more globes reduces their brightness. Each globe shares the voltage.

Parallel Circuit

the circuit has a number of independent branches that can have individual switches. A globe failing in one branch does not affect the other branches. Brightness is maintained as more globes are added. Each branch receives the full voltage.

Page 200 video and Page 201 comparing circuits and bulb brightness.

House current - Extremely Dangerous. Parallel circuit - 240 V and 50 cycles per second AC (alternating current) flows in both directions. Likely to kill.

Batteries current - Dangerous. DC (direct current) - only flows in one direction.

Active wire - Brown plastic - carries current to the power point

Neutral wire - Blue plastic - carries current away from the power point

Earth wire - Green/Yellow plastic - connects the power point and any metal part of the appliance to the ground - a dangerous stray current will go to the earth, rather than through you.

Fuse - a wire of high resistance and low melting point - if the current becomes too high, it melts and breaks the circuit. Difficult to reset. Found in older homes.

Circuit breaker - is a switch that is activated by higher than allowable current - it flips off automatically - easy to reset.

Safety switch - also known as an RCD (residual current device) found in all modern home power boards. Monitors the current into and out of the house - these should always be equal. If they are not equal, then it is likely the current is leaking out from a faulty appliance or via a person - reacts in 0.03 sec - you still get a shock but hopefully not enough to kill you.

Ch 6.4 Electromagnets, motors and generators

Blue and Aqua here

Magnetism an invisible field that exerts force on iron, cobalt or nickel.

Electromagnetism a magnetic field produced by an electric current

2 PhET magnet and solenoid simulations

Cool UK - electromagnetism and motors

Solenoid - a looped current carrying coil of wire

Electromagnet - a magnet created by an electric current - can be controlled by varying the current ON-OFF. eg include junk yard, iPod, phone, speakers, microphone, circuit breakers

Electric motors

Electric Motor - a current carrying coil of wire will spin in the field of a permanent magnet - this is the opposite to a generator.

Generator - a coil of wire is made to spin in the field of a permanent magnet - this produces an electric current - this is the opposite to an electric motor

Turbine - a large generator - the coil is kept still and the magnet spins around it eg bicycle light generator, steam, wind turbines, hydro-electric, wave power and tidal power.

Page 211 video on wind farms

AC/DC and Transmission

AC - Alternating current - the electrons shuffle back and forwards at 50 cycles per second or 50 Hertz. Can generate more power, easier to transmit and its voltage can be changed by transformers. Has to be converted to DC to be stored.

DC - Direct current - the electrons flow in one direction only. Only suitable on small appliances. Easy to store

Transmission - Very high voltage and very low current eg 500 000 V. This reduces the lost energy. However home users require a much lower voltage - so transformers are used to step voltages up or down as required.

Worksheet – Snowy Mountains Scheme page 213

Revision checklist

Chapter Revision Test from the Resources Tab of the Textbook.

The Worksheets 6.1 and 6.2

Unit Review Questions x 4

Prac write ups