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Electricity Can you fill in the symbols for the circuit components using page 176 and 181

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Todays lesson Electrical symbols Charge Series and Parallel circuits Understand that current is the rate of flow of charge Recall and use: Q = It Looking at current in different circuits Conventional current

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cell energy electron lamp

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cell energy electron lamp Can you copy this please?

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Electrons Hi, Im Eleanor the electron.

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Coulomb of charge (electrons) Think of it as a bag of electrons (containing 6000000000000000000 electrons!)

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Current The number of Coulombs flowing past a point in the circuit every second. I = Q/t A Im counting how many coulombs of electrons go past me every second 1 Amp = 1 coulomb per second

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Current The number of Coulombs flowing past a point in the circuit every second. I = Q/t A Im counting how many coulombs of electrons go past me every second 1 Amp = 1 coulomb per second Can you copy this please?

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Lets build some circuits! Do experiments 31.4 to 31.10 page 256- 257

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In a series circuit Current is the same at any point in the circuit 2.5 A

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In a series circuit Current is the same at any point in the circuit 2.5 A Can you copy this please?

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Todays 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

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

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

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Milliamps! 1 A = 1000 mA 1 mA = ?

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

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Stand up!

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

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

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Voltage Voltage is the amount of energy transferred (changed) per coulomb of charge.

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Lets build some circuits!

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Stand up!

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

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

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Stand up!

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

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

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Todays lesson Understand the term resistance Recall and use: V =IR

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Stand up!

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Resistance Measures how difficult it is for current to flow. Measured in Ohms (Ω) VA Resistance = voltage/currentR = V/I

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Resistance Measures how difficult it is for current to flow. Measured in Ohms (Ω) VA Resistance = voltage/currentR = V/I Can you copy this please?

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Ohms Law V = IR V R I X

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Lets measure a resistance!

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Resistance of a lamp AV Resistance = voltage/currentR = V/I Vary the voltage and current using a variable resistor (rheostat). Plot a graph of resistance against current

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Resistance of a lamp V(V)I(A)R(Ω) I(A) R(Ω)

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Homework! Read pages 176 and 177 Answer questions on page 177 Due Wednesday 25 th November

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Resistance of a lamp As the current in a lamp increases, it gets hotter, and its resistance increases. Why?

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Resistance of a lamp As the current in a lamp increases, it gets hotter, and its resistance increases. Copy please.

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Lets try some resistance questions

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Todays lesson Understand the term power Recall and use: P =VI Recall and use E = VIt

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Power The amount of energy used by a device per second, measured in Watts (Joules per second) VA Power = voltage x currentP = VI

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

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Power of a lamp AV Power = voltage x currentP = VI Measure the power of the lamp at its operating voltage. What is the electrical energy being turned into?

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

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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

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

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

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

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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)

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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

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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

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Simple!

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Lets try some questions!

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© Boardworks Ltd 2003 KS4 Electricity – Resistance.

© Boardworks Ltd 2003 KS4 Electricity – Resistance.

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