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

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

cell energy electron lamp

cell energy electron lamp Can you copy this please?

Electrons Hi, Im Eleanor the electron.

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

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

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?

Lets build some circuits! Do experiments 31.4 to page

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

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

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

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

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

Milliamps! 1 A = 1000 mA 1 mA = ?

Milliamps! 1 A = 1000 mA 1 mA = A

Stand up!

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

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

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

Lets build some circuits!

Stand up!

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

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?

Stand up!

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

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?

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

Stand up!

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

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?

Ohms Law V = IR V R I X

Lets measure a resistance!

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

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

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

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

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

Lets try some resistance questions

Todays 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) VA Power = voltage x currentP = VI

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?

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?

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

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) VA Power = voltage x currentP = 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)

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

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 = J P I V X

Simple!

Lets try some questions!