Starter - A.C and D.C electricity

1. Draw diagrams to help you explain the difference between A.C and D.C electricity.

2. A.C or D.C. providers? BatterygeneratorSolar cell

P6 – Electricity for Gadgets

Lesson 11 – The Dynamo effect

Learning aim: Demonstrate an understanding of how a current and voltage can be induced in a wire

Learning Objectives Success Criteria

Understand how a dynamo generates electricity.

Understand how a voltage is induced.

Understand how changes in magnetic field affect induced voltage.

Describe and recognise the dynamo effect and how electricity can be generated.(Grade E-D)

Label a diagram of an a.c. generator showing the coil, magnets, slip rings and brushes. (Grade E-D)

Understand the interaction between a wire carrying current and magnetic field.(Grade C)

Explain what affects the size of the induced voltage

(Grade C-A)

AC/DC

What is AC?

AC is alternating current, a current which is constantly changing in direction.

What is DC?

DC is direct current, current that is always flowing in one direction.

Source of AC?

Mains electricity (50Hz)

Sources of DC?

Cells or batteries

Electromagnetic Induction

N

The direction of the induced current is reversed if…

1) The wire is moved in the opposite direction

2) The field is reversed

The size of the induced current can be increased by:

1) Increasing the speed of movement

2) Increasing the magnet strength

Flemings Right Hand Rule

What effects the size of the induced voltage?

Name the three things that effect the size of the induced voltage :

1) The strength of the magnetic field

2) The speed the wire cuts magnetic field lines

3) The length of the wire (in the field)

HT

Electromagnetic induction

Electromagnetic induction

The direction of the induced current is reversed if…

1) The magnet is moved in the opposite direction

2) The other pole is inserted first

The size of the induced current can be increased by:

1) Increasing the speed of movement

2) Increasing the magnet strength

3) Increasing the number of turns on the coil

AC Generator (P6f01 Q1)

Look at the diagram of a generator. Add the labels and describe the purpose of each of the key parts (use p252 to help)

Magnetic polesCoilBrushesSlip ring commutator

WS answersQ1a magnet and wire with

relative movement • Q1b – see diagram on page 252 of the Student Book for labels • Q1c N on left, S on right • Q1d generator produces a.c. an electric cell d.c.

Generating Electricity When a magnet is moved though a coil of wire an electric current is produced in the coil. We can show this using a galvanometer. This is like a very sensitive ammeter. The needle shows which direction the current is flowing and also how large the current is.

Galvanometer

Coil of wire

0

Magnet

N S

Movement

The diagram shows a magnet being pushed slowly into the coil. The galvanometer is showing the size and the direction of the current caused For each of the drawings in the boxes show where you think the galvanometer needle will be.

Galvanometer

Coil of wire

0

Magnet

Movement

N S N

Galvanometer

Coil of wire

0

Magnet

Movement Galvanometer

Coil of wire

0

Magnet

No Movement

Galvanometer

Coil of wire

0

Magnet

Movement

Galvanometer

Coil of wire

0

Magnet

Movement (Fast) Galvanometer

Coil of wire

0

Magnet

Movement (Very slow)

S S

S N

N

N

S

S

N

N

P2.3.3

Flemings Right Hand Rule

What do these represent?What is electromagnetic induction used for in the real world?

R ig idfra m e F lex ib le

d iap h ra g m

C o il

To am p lifie r

C y lin d r ic a lm ag n et S

N

N

Moving Coil Microphone

How does the microphone work?

plenary

Learning Objectives Success Criteria

Understand how a dynamo generates electricity.

Understand how a voltage is induced.

Understand how changes in magnetic field affect induced voltage.

Describe and recognise the dynamo effect and how electricity can be generated.(Grade E-D)

Label a diagram of an a.c. generator showing the coil, magnets, slip rings and brushes. (Grade E-D)

Understand the interaction between a wire carrying current and magnetic field.(Grade C)

Explain what affects the size of the induced voltage

(Grade C-A)

Electromagnetic induction

What will happen if you move a magnet into a coil of wire?

A current is induced in the coil.

Only when the magnet is moving.

Stationery magnet

What happens when the magnet is in the coil?

Nothing!!

A current is only induced when the magnet is moving.

Electromagnetic induction

What will happen if you move the magnet out of the coil of wire?A current is induced in the coil.

This time in the opposite direction.

If you reverse the direction of the movement, then you reverse the direction of the current.

AC or DC?

What will happen if you move a magnet in and out of the coil repeatedly?

A current will be induced in the coil, the current will flow in one direction and then reverse and flow in the opposite direction.

What type of current is this? Alternating current

Plenary

Answer these questions? in your book• What happens when the wire is moved

through the magnetic field

• What does the ammeter show you

• The current is called an ……………………… Current

• Who discovered how to make electricity using magnetism

• Which direction is the current flowing?

Lenz's law :

The direction of the induced current is such that it opposes the change producing it