MHW5 reviewPeer assess motor homeworkUse pg 251 to help

P6 – Electricity for Gadgets

Lesson 12 – AC generators

Learning aim: Demonstrate an understanding of how an alternating current generator works

Learning Objectives Success Criteria

Recognise electrical generators and why they are used.

Understand how size and/or frequency of voltage can be increased.

Explain how an a.c. generator works.

Describe a generator in comparison to a motor.(Grade E-D)

Explain why electricity is useful.

(Grade E-D) Recall what frequency mains electricity

is supplied at in the U.K. (Grade E-D) Explain why the rotation of a magnet

inside a coil of wire induces an (AC)alternating current.(Grade C)

Recall where and how mains electricity is generated. (Grade C)

Describe what affects the size and frequency of the voltage generated.(Grade C)

Use a diagram to explain how an a.c. generator works including the action of the slip rings and brushes.(Grade C-A)

MHW6Find out the circuit symbol for a

diode and what a diode is

Dynamo

Generator (Alternator)

Electric motors vs. generators

Electric motors convert electricity to

mechanical energy in order to do work

Generators convert mechanicalenergy to electrical energy

Generator – now build your own p6f 02(either AC or DC)

Use the diagram on p255 to help

.

X X

.

N

S

+

-

NN

SS

+

-

E

t

The Generator (dc)

The keywords are

Direct current Commutator

DC Generator

1. The diagram shows a rectangular coil PQRS which can rotate about an axis which is perpendicular to the magnetic field between two magnetic poles.

P

Q R

S

N p o leS p o le

I I

Explain why the coil begins to rotate when the direct current I is switched on.

Try worksheet p6f02Q1 and 2

HT Q3

WS answersQ1 a) electrical; kinetic; b) kinetic;

electrical; c) left; d) commutator; current; half; e) magnetic; voltage; induced; f) generator; right g) induced; increasing; turns; increasing; strength; increasing; magnetic; h) coil; slip; i) coil; commutator • Q2a d.c. – commutator; a.c.– slip rings and brushes • Q2b more turns on coil; stronger magnets; spin faster • Q2c power station – uses electromagnets; electromagnets spin and stator coils are stationary; much bigger in size, etc. •

WS answerQ3a the coil moving through the magnetic field

has a current induced in it and the slip rings attached to the ends deliver the current to the brushes which press against them; the current alternates in direction because each side of the coil passes down through the field on one side and then up through the field on the other side • Q3b one complete cosine wave • Q3c(i) goes to zero • Q3c(ii) because the magnetic field in the coil is not changing at that instant • Q3d(i) horizontal as in diagram • Q3d(ii) the magnetic field in the coil is changing rapidly at that instant • Q3e a cosine wave with a higher peak and at twice the frequency.

HT

How can motion produce a current?plenary

Learning Objectives Success Criteria

Recognise electrical generators and why they are used.

Understand how size and/or frequency of voltage can be increased.

Explain how an a.c. generator works.

Describe a generator in comparison to a motor.(Grade E-D)

Explain why electricity is useful.

(Grade E-D) Recall what frequency mains electricity

is supplied at in the U.K. (Grade E-D) Explain why the rotation of a magnet

inside a coil of wire induces an (AC)alternating current.(Grade C)

Recall where and how mains electricity is generated. (Grade C)

Describe what affects the size and frequency of the voltage generated.(Grade C)

Use a diagram to explain how an a.c. generator works including the action of the slip rings and brushes.(Grade C-A)

Plenary

Complete worksheet P6d6 – summary of motors and generators.