Boardworks Ltd 2003 Drawing circuit diagrams You must

Drawing circuit diagrams • You must have – Straight lines – Sharp corners – Use the correct symbols © Boardworks Ltd 2003

Circuit symbols Light bulb © Boardworks Ltd 2003

Can you remember…. ? Component Battery Wire Bulb Buzzer Symbol © Boardworks Ltd 2003

Which light bulbs will light? A B C D © Boardworks Ltd 2003

A complete circuit For electricity to flow in a circuit it must be able to flow from one end of the battery to the other end © Boardworks Ltd 2003

Electricity does not only flow inside wires! • Lots of materials let electricity flow through them. • An electrical conductor allows electricity to flow through it. • An electrical insulator does not allow electricity to flow through it. © Boardworks Ltd 2003

Testing to see if a material is an electrical conductor or an insulator Set up the circuit shown and place different materials in the gap in the circuit. Record which materials let electricity through (the bulb lights if electricity flows). What do we call a material that lets electricity flow through it? CONDUCTOR What do we call a material that does not let electricity flow through it? INSULATOR © Boardworks Ltd 2003

Electron Flow © Boardworks Ltd 2003

Electron flow Electricity in wires is a flow of electrons along the wire from the negative end of the battery to the positive end What do we call this flow of electrons? Electrical current © Boardworks Ltd 2003

Voltage is a measure of how big a push The v_____ lectrons are given as they leave the e_______ attery The bigger the voltage, the bigger b_____. ush the p___. lamps © Boardworks Ltd 2003

Measuring voltage The unit of measure for voltage is the volt, symbol V. Voltage is measured using an voltmeter. . V © Boardworks Ltd 2003

Current ircuit current is the flow of In an electric c____, lectrons carrying electrical energy. The e_______ bigger the current, the m___ ore electrons are flowing around the circuit. lamps © Boardworks Ltd 2003

Measuring current The unit of measure for current is the amp, symbol A. Current is measured using an ammeter. A © Boardworks Ltd 2003

Set up the two circuits shown: A. BRIGHTER B. DIMMER What do happens The Series we Parallel In circuit call other ifare Circuit circuit you Circuit circuit Athe bulb the unscrew B? A? stays goes bulbsthe out. lit. a are one bulb the bulb inbrightest. circuit in Circuit B? A? In which circuit bulbs brightest? © Boardworks Ltd 2003

A series circuit • All bulbs will glow dimmer! © Boardworks Ltd 2003

Old Christmas tree lights • If one bulb breaks the circuit is broken - all bulbs go out! © Boardworks Ltd 2003

A Parallel circuit • The bulbs all glow brightly! © Boardworks Ltd 2003

Example: In new christmas tree lights • If one bulb is broken the other bulbs can still light © Boardworks Ltd 2003

Think • How do you think lights on a xmas tree are set up? • What about street lamps? • Lights in a car? • Lights in your house – between rooms? © Boardworks Ltd 2003

Series circuit – 1 bulb © Boardworks Ltd 2003

Series circuit – 2 bulbs © Boardworks Ltd 2003

Parallel Circuit © Boardworks Ltd 2003

Resistance is how much a material tries to stop electricity passing through it!!! The symbol = R Measured in Ohms . using an Ohmmeter. © Boardworks Ltd 2003

Experiment: How are current and voltage related as electricity flows through resistor? © Boardworks Ltd 2003

The two quantities current and voltage are directly proportional. x x x The graph of current against voltage is a straight line Current / A Current-voltage graph for a resistor x x x Voltage/ A Ohm’s Law The voltage and the current in a circuit are directly proportional to each other when resistance and temperature are constant © Boardworks Ltd 2003

Resistance Calculating resistance © Boardworks Ltd 2003

Ohms law triangle Whatever you are trying to find cover it up and it will leave you with the calculation that you need. So if you are trying to find current (I). . . …cover up I… …which gives the formula… V I R V I = R x © Boardworks Ltd 2003

A bulb has a current of 20 A and a voltage of 100 V What is the resistance? R = V I = 100 V 20 A = 5 © Boardworks Ltd 2003

The everyday uses of electricity © Boardworks Ltd 2003

1. The heating effect of an electric current • Applications: irons, kettles etc © Boardworks Ltd 2003

The magnetic effect of an electrical current • Application : electric motor. © Boardworks Ltd 2003

The chemical effect of an electrical current • An electrical current can cause chemical reactions to happen! • Application: when electricity is passed through water it breaks up into oxygen and hydrogen gas! © Boardworks Ltd 2003

Hydrogen gas can then be used as a fuel © Boardworks Ltd 2003

Simple Circuits 1. A complete circuit is required for electric current to flow 2. Circuits can be drawn using circuit diagrams with correct symbols 3. Components can be arranged in series or parallel