Electric charge Electric charge can be either positive or negative. COVERED UNDER ELECTRIC CHARGE BY TRIPLE GROUPS ONLY Electric charge Electric charge can be either positive or negative. In an atom an electron has a negative charge that is of the same size as the positive charge of a proton. Neutrons have no electric charge. As an atom has the same number of electrons as protons it is uncharged.

Electric circuits An electric current will only flow if there is a complete, unbroken electric circuit, that contains a power supply. A circuit diagram uses a standard set of symbols to show how electrical components are connected together.

Circuit symbols cell a cell is required to push electrons around a circuit battery a battery consists of two or more cells wire wires should always been drawn as straight lines wire junction switch a switch enables the current in a circuit to be turned on or off

old symbol – the indicator symbol is now used often a light bulb – this is used to show whether or not a circuit is on light bulb old symbol – the indicator symbol is now used A ammeter measures electric current in amperes (A) V voltmeter measures voltage in volts (V)

fixed resistor a resistor is used to limit the current in a circuit variable resistor thermistor a device whose resistance decreases with temperature light dependent resistor (LDR) a device whose resistance decreases with brightness

diode a diode only allows current to flow in one direction (indicated by the arrow) light emitting diode (LED) a diode that emits light when it allows the flow of electric current fuse a fuse is designed to melt and so break an electric circuit when too much electric current flows heater a device used to convert electrical energy to heat

The arrow shows the direction of electron flow. Electric current An electric current is the rate of flow of electric charge. An electric current of one ampere (A) flows when a charge of one coulomb (C) passes a point in an electric circuit in one second In metallic conductors (e.g. copper wire) electrons carry negative charge from the negative side of a power supply, around a circuit and back into the positive side. The arrow shows the direction of electron flow.

In a series circuit Current is the same at any point in the circuit Do Now Can you copy this please? Next draw a parallel circuit with two branches 2.5 A 2.5 A

Today’s lesson Looking at current in different circuits Recall and use: Q = It Understand that voltage is the number of joules per coulomb transferred Looking at voltage in different circuits

In a parallel circuit The current splits (total current stays the same) 2.5 A 2.5 A 1.25 A 1.25 A

Can you copy this please? In a parallel circuit The current splits (total current stays the same) 2.5 A 2.5 A 1.25 A ☺ 1.25 A Can you copy this please?

Milliamps - conversions 1 A = 1000 mA 1 mA = ?

Milliamps! 1 A = 1000 mA 1 mA = 0.001 A

Electrical conductors and insulators COVERED UNDER ELECTRIC CHARGE Electrical conductors and insulators An electrical conductor is a material through which electric current flows easily. All metals are conductors. Electrical insulators have a very high resistance to the flow of electric current. Complete the table below: copper conductor rubber insulator steel mercury paper plastic diamond graphite 1 2 3 4 5 6

Charge-current equation electric charge = current x time Q = I x t also: I = Q ∕ t and: t = Q ∕ I charge current time

Question 1 Calculate the charge passing through a device when a current of 500mA flows for 3 minutes. Q = I x t = 500 mA x 3 minutes = 0.5A x 180s charge = 90C

Question 2 Calculate the current flowing when a charge of 240C flows through a device in 80s. I = Q ÷ t current = 240 C 80s current = 3A Now complete the questions on the sheet.

Do Now - Please copy and complete Complete: Q I t 60 C 2 A 13 A 5 s 960 C 4 minutes 3 C 50 mA

Learning today Understand that voltage is the number of joules per coulomb transferred Looking at voltage in different circuits The definitions of emf and pd The advantages of connecting bulbs in parallel.

Complete: Answers 30 s 65 C 4 A 60 s Q I t 60 C 2 A 13 A 5 s 960 C 4 minutes 3 C 50 mA 30 s 65 C 4 A 60 s

Voltage A battery gives electrical charge energy. The voltage of a battery is equal to the energy in joules provided when a charge of one coulomb passes through the battery. voltage = energy ÷ charge 1 volt is the same as 1 joule per coulomb

Voltage(emf) ☺ V I’m checking the difference in energy (per coulomb) between the 2 red arrows 1 Volt = 1 Joule per coulomb

Voltage (p.d.) ☺ I’m checking the difference in energy (per coulomb) before and after the lamp V 1 Volt = 1 Joule per coulomb

Voltage – copy Voltage V is the amount of energy transferred (changed) per coulomb of charge. Unit – volts V It is measured with a voltmeter in parallel 1 volt is the same as 1 joule per coulomb The unit is named after the scientist Volta famous for making the first batteries

Choose appropriate words to fill in the gaps below: Electric current is the rate of flow of electric _______. Electric charge is measured in _________. A battery provides electrical _______ . The amount of energy provided per _________ of electric charge passing is equal to the ________ of the battery. The _______ supply gives 230 ________ to every coulomb of charge. charge coulombs energy coulomb voltage mains joules WORD SELECTION: coulombs charge mains joules coulomb voltage energy

EMF and PD Electromotive force is please copy the definitions on page 179 Potential difference is

EMF and PD both have the volt as a unit The electromotive force (emf) of a cell or a power supply is the work done per unit of charge by the cell in driving charge around a complete circuit (including the cell itself The potential difference (PD) across a component is the work done per unit of charge in driving charge through the component.

In a series circuit The sum of the voltages across the lamps equals the voltage across the cells 9 V 3 V 3 V 3 V

Can you copy this please? In a series circuit The sum of the voltages across the lamps equals the voltage across the cells 9 V ☺ 3 V 3 V 3 V Can you copy this please?

In a parallel circuit In a simple parallel circuit, voltage across each lamp equals the voltage across the cells 5 V 5 V 5 V

Can you copy this please? In a parallel circuit In a simple parallel circuit, voltage across each lamp equals the voltage across the cells 5 V 5 V ☺ 5 V Can you copy this please?

Do Now Ammeter & Voltmeter

Learning today The advantages of connecting bulbs in parallel. Resistance

Electric current flow – conventional current Electric current flows from the POSITIVE terminal of a power supply around a circuit to the NEGATIVE terminal. The longer thinner line of the symbol for a cell is the positive terminal. In the circuit above the diode is aligned so that it allows current to flow through the radio.

Series circuits Circuit components are said to be connected in series if the same electric current passes through each of them in turn. 3A 3A 3A 3A 3A 3A 3A The cell and the two lamps are in series with each other and so the same electric current passes through all of them.

Parallel circuits The voltage across each component connected in parallel is the same. The voltmeter reading for component X, V1 will be the same as the voltmeter reading for component Y, V2.

In a series circuit all of the components can be controlled by using just one switch. Each component shares the voltage of the power supply and so adding more bulbs in series will cause each bulb to become dimmer.

In a parallel circuit all of the components can be individually controlled by using separate switches. If one light bulb blows the other bulbs will still carry on working.

Exercise What are the advantages of connecting two lamps in parallel rather than in series to a power supply? When connected in parallel: the lamps are brighter than when connected in series the lamps can be controlled individually with switches one lamp will continue working even if the other does not

Currents in parallel circuits The total current through the whole circuit is the sum of the currents through the separate components. 5A 5A 3A 3A 2A 2A

Calculate the currents measured by ammeters A1, A2 and A3 in the circuit below.

Question Draw a circuit diagram for the torch shown below.

Choose appropriate words to fill in the gaps below: When components are _________ together in series they will all have the same _________ flowing through each of them. When components are connected in parallel to each other they will each have the same _________. Lamps are usually connected in __________ to each other as this allows them to be controlled individually by _________ and if one lamp _______ the others can still continue to operate. connected current voltage parallel switches blows WORD SELECTION: blows current switches parallel connected voltage

Online Simulations Fifty-Fifty Game on Conductors & Insulators - by KT - Microsoft WORD Signal Circuit - PhET - Why do the lights turn on in a room as soon as you flip a switch? Flip the switch and electrons slowly creep along a wire. The light turns on when the signal reaches it. Charge flow with resistors in series and parallel - NTNU Circuit Construction DC Only - PhET - An electronics kit in your computer! Build circuits with resistors, light bulbs, batteries, and switches. Take measurements with the realistic ammeter and voltmeter. View the circuit as a schematic diagram, or switch to a life-like view. Simple parallel circuit with motor and lamps - Freezeway.com Simple parallel circuit with motor and lamps and a short circuiting switch - Freezeway.com Switch quiz circuit - Freezeway.com Two way switches with a flight of stairs - Freezeway.com Bulb circuit diagram quiz - Freezeway.com Hidden Pairs Game Circuit Pairs Quiz basic circuit symbols with this pairs game - by eChalk Hidden Pairs Game on Circuit Symbols - by KT - Microsoft WORD Electric Current Quizes - by KT - Microsoft WORD BBC KS3 Bitesize Revision: Circuit symbols Series and parallel circuits Measuring current and voltage Current in series circuits BBC AQA GCSE Bitesize Revision: Circuit symbols & diagrams Series & parallel connection Current & potential difference Cells and circuits Series circuits Parallel circuits

Today’s lesson Understand the term power Recall and use: P =VI Recall and use E = VIt

Power The amount of energy used by a device per second, measured in Watts (Joules per second) A V Power = voltage x current P = VI

Can you copy this please? Power The amount of energy used by a device per second, measured in Watts (Joules per second) ☺ A V Can you copy this please? Power = voltage x current P = VI

Power of a lamp A V Power = voltage x current P = VI Measure the power of the lamp at it’s operating voltage. What is the electrical energy being turned into? A V Power = voltage x current P = VI

Example A 200 W television is plugged into the 110V mains. What is the current in the television? P I V X

Example A 200 W television is plugged into the 110V mains. What is the current in the television? I = P/V = 200/110 = 1.8A P I V X

Example A kettle uses 240V and 8A. What is its power? P I V X

P V I Example A kettle uses 240V and 8A. What is its power? P = VI = 240x8 = 1920W (=1.9kW) P I V X

Remember Power is the amount of energy used by a device per second, measured in Watts (Joules per second) A V Power = voltage x current P = VI

Total energy So the total energy transformed by a lamp is the power (J/s) times the time the lamp is on for in seconds, E = VIt E = energy transformed (J) V = Voltage (also called p.d.) I = current (A) t = time (s)

P V I Example A kettle uses 240V and 8A. What is its power? P = VI = 240x8 = 1920W (=1.9kW) How much energy does the kettle use in 5 minutes? P I V X

P V I Example A kettle uses 240V and 8A. What is its power? P = VI = 240x8 = 1920W (=1.9kW) How much energy does the kettle use in 5 minutes? E = VIt = 240x8x300 = 576000 J P I V X

Simple!

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