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© Boardworks Ltd 2003 IGCSE Electricity – Simple Circuits

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© Boardworks Ltd 2003 Current state that current is related to the flow of charge use and describe the use of an ammeter show understanding that a current is a rate of flow of charge and recall and use the equation l = Q/t distinguish between the direction of flow of electrons and conventional current

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© Boardworks Ltd 2003 Circuit symbols Instead of drawing intricate diagrams of electrical components we use circuit symbols to simplify how circuits are set up. You will need to learn these, how to draw them, and how to identify them. Filament lamp

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© Boardworks Ltd 2003 Use a textbook or other resource to fill in the table below: ComponentCircuit symbol Fuse Switch Resistor Motor M

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© Boardworks Ltd 2003 ComponentCircuit symbol Cell Voltmeter Battery Ammeter A V Use a textbook or other resource to fill in the table below:

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© Boardworks Ltd 2003 Breaks in circuits Set up the circuit shown…. …does the bulb light? Why does the bulb not light? There is a break in the circuit. For electricity to flow in a circuit it must be able to flow from one terminal of the cell or battery to the other terminal. NO

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© Boardworks Ltd 2003 Letting electricity pass Do all materials let electricity pass? Which materials will and which materials will not? 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

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© Boardworks Ltd 2003 Which of these bulbs will light? Build the circuits! A. B. C. x x Electricity will always take the easiest path. It is easier to flow through a wire than through the bulb. So in circuits B and C the electricity does not pass through the bulb. The cell or battery still loses energy because, electricity is still flowing. This type of circuit is known as a SHORT CIRCUIT.

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© Boardworks Ltd 2003 Electron flow Electricity in wires is a flow of electrons along the wire. What do we call this flow of electrons? Electrical current

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© Boardworks Ltd 2003 When we talk about current flowing we say that current flows out of the positive terminal of the cell and back into the negative terminal. Current Flow Conventional Current What do we call this flow?

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© Boardworks Ltd 2003 However, the electrons flow from the negative side of the battery to the positive side. These are the particles which are actually moving through the conductor. Electron Flow

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© Boardworks Ltd 2003 When electrons were discovered, physicists worked out what was really happening. Negatively charged electrons are repelled out of the negative terminal of the cell. They then travel round the circuit and are attracted back to the positive terminal. Conventional current and Electron flow Conventional current electrons Conventional current What charge do electrons have? Negative What do two negative charges do if placed near to each other? They will repel each other. What will a positive and a negative charge do to each other? They will attract each other.

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© Boardworks Ltd 2003 In an electric c____, current is the flow of c_______. The bigger the current, the m___ charge is flowing around the circuit. The w___ carry the electrons from one terminal around the circuit to the other t______. Current lamps ircuit harge ore ires erminal

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© Boardworks Ltd 2003 Current Current=Charge/time I=Q/t Q is measured in Coulombs (C) t is measured in seconds (s) I is measured in Amperes (A)

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© Boardworks Ltd 2003 Set up the two circuits shown: In which circuit are the bulbs the brightest? BRIGHTER DIMMER A. B.

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© Boardworks Ltd 2003 Measuring current To find the current through a component connect an ammeter next to the component (in series) Make sure the + side of the ammeter is connected nearest to the + side of the power supply All of the current flowing through the component must pass through the ammeter Now measure the current in each bulb in your circuits

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© Boardworks Ltd 2003 Set up the two circuits shown: Which bulbs have the largest current? MORE CURRENT LESS CURRENT A. B.

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© Boardworks Ltd 2003 Charge, current and time We can express a relationship between charge, current and time mathematically using the equation: Charge = Current x time Q=It Charge measured in Coulombs (C) Current measured in Amps (A) Time measured in seconds (s)

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© Boardworks Ltd 2003 Formula triangles Q I tt x Formula triangles help you to rearrange formula, the triangle for Q=It is shown below: Whatever quantity you are trying to find cover it up and it will leave you with the calculation required. So if you were trying to find current, I….. …you would cover I up… …and you are left with the sum… I = Q t

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© Boardworks Ltd 2003 A current of 6A flows for 3 minutes. How much charge flows? Q= It = 6A x (3x60)s = 1080 C In an examination you will not gain a mark for just writing Q=It. You must write out the whole formula: Charge = Current x time Always convert time to seconds!!!

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© Boardworks Ltd 2003 To do P Answer questions 1-4

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© Boardworks Ltd 2003 Progress check state that current is related to the flow of charge use and describe the use of an ammeter state that current is a rate of flow of charge use the equation l = Q/t distinguish between the direction of flow of electrons and conventional current

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