Do now!Can you finish the questions you started last lesson?

Last lesson - Electromagnetic inductionIf a magnet is moved inside a coil an electric current is induced (produced)COPY this please!

Electromagnetic inductionA electric current is induced because the magnetic field around the coil is changing.

Generator/dynamoA generator works by rotating a coil in a magnetic field (or rotating a magnet in a coil). A slip-ring commutator produces alternating current (a.c.)Can you stick this in please?

COPY this please!

Todays lesson - Transformers

Stand up!

cellenergyelectronlamp

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

CurrentThe number of Coulombs flowing past a point in the circuit every second.

Im counting how many coulombs of electrons go past me every second1 Amp = 1 coulomb per second

In a series circuitCurrent is the same at any point in the circuit2.5 A2.5 A2.5 A2.5 A

In a parallel circuitThe current splits (total current stays the same)2.5 A2.5 A1.25 A1.25 A

Voltage(emf)Im checking the difference in energy (per coulomb) between the 2 red arrows1 Volt = 1 Joule per coulomb

Voltage (p.d.)Im checking the difference in energy (per coulomb) before and after the lamp1 Volt = 1 Joule per coulomb

In a series circuitThe sum of the voltages across the lamps equals the voltage across the cells9 V3 V3 V3 V

In a parallel circuitIn a simple parallel circuit, voltage across each lamp equals the voltage across the cells5 V5 V5 V

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

Ohms LawV = IRCan you copy this please?

PowerThe amount of energy changed/transformed by a device per second, measured in Watts (Joules per second)Power = voltage x currentP = VI

Todays lesson - TransformersCan you gather around Mr Porter?

TransformersA transformer consists of 3 main parts

TransformersA changing current in the primary coil produces a changing magnetic field in the core. This changing magnetic field induces a changing current in the secondary coil.

Changing voltagesThe ratio of the number of turns on the coils equals the ratio of the voltages

Vp/Vs = Np/Ns# of turns = Ns# of turns = Np

Changing voltagesA transformer where the voltage rises is called a step-up transformer

Changing voltagesA transformer where the voltage falls is called a step-down transformer

No energy for nothingHowever, no new energy is made

No energy for nothingPower in = power outVpIp = VsIs

a.c. onlyBecause transformers rely on induction (changing fields), they only work with alternating current (a.c.)

Why do we need transformers?

Why do we need transformers?Current flowing through wires causes them to get hot and energy is lost.

Why do we need transformers?Keeping the current low means electricity can be transported long distances without losing too much energy.

Why do we need transformers?However, in order to send a large quantity of energy, high voltages are needed.

Transmission of ElectricityStep-upStep-down

Lets try some questions!Page 221 Question 3Page 223 Questions 2 & 3Page 225 Questions 3, 6 & 7Mr Porter wants you to finish these for homework PLUS the questions he is now giving you. Due Tuesday 20th Oct.

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