Transcript Electromagnetism

Electromagnetism
•Syllabus
•Lesson 01 – The Motor Effect
•Lesson 02 – Induction
Home
Syllabus - Single Science IGCSE
Magnetism
 6.2 recall that magnets repel and attract other magnets, and attract magnetic substances
 6.3 recall the properties of magnetically hard and soft materials
 6.4 understand the term ‘magnetic field line’
 6.5 understand that magnetism is induced in some materials when they are placed in a magnetic field
 6.6 sketch and recognise the magnetic field pattern for a permanent bar magnet and that between two bar magnets
 6.7 know how to use two permanent magnets to produce a uniform magnetic field pattern
Electromagnetism
 6.8 recall that an electric current in a conductor produces a magnetic field round it
 6.9 describe the construction of electromagnets
 6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current
 6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
 6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and, how this effect is applied in simple d.c. electric motors
and loudspeakers
 6.13 predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
 6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the
current
Electromagnetic induction
 6.15 recall that a voltage is induced in a conductor when it moves through a magnetic field or when a magnetic field changes through a coil; also
recall the factors which affect the size of the induced voltage
 6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also
describe the factors which affect the size of the induced voltage
 6.17 recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different
numbers of turns on the input and output sides
 6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy
 6.19 recall and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer
 secondary turns / primary turns = output (secondary) voltage / input (primary) voltage
 6.20 recall and use the relationship
 input power = output power VP IP = VS IS for 100% efficiency
Home
Syllabus – Double IGCSE
Magnetism and electromagnetism
 understand the term ‘magnetic field line’ (P2.19)
 recall that an electric current in a conductor produces a magnetic field
round it (P2.20)
 recall that a force is exerted on a current-carrying wire in a magnetic field,
and, how this effect is applied in simple d.c. electric motors and
loudspeakers (P2.21)
 predict the direction of the resulting force when a wire carries a
current perpendicular to a magnetic field (P2.22)
 recall that the force on a current-carrying conductor in a magnetic field
increases with the strength of the field and with the current (P2.23).
Electromagnetic induction
 recall that a voltage is induced in a conductor when it moves through a
magnetic field or when a magnetic field changes through a coil; also recall
the factors which affect the size of the induced voltage (P2.24)
 describe the generation of electricity by the rotation of a magnet within a
coil of wire and of a coil of wire within a magnetic field; also describe the
factors which affect the size of the induced voltage (P2.25).
Home
The Motor Effect
09/04/2016
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor
Home
Fields Bar Magnets
Single Science Only
handout
Home
Opposite Poles
Single Science Only
Home
Same Poles
Single Science Only
Home
Fields due to Current
Home
Single Science Only
Single Coil of Wire
Solenoid
Home
Magnetic Field Lines


There are magnetic field lines around every
 Magnet
 Electrical wire (with current flowing through it)
Anything magnetic in the field will experience a force
Movie
Home
Wire in a magnetic field
Home
The Catapult (Motor) Effect
Home
Motor Effect


If a conductor carrying an electric current moves
through magnetic field lines at right angles it will
experience a force.
A charged particle will experience the same effect
Home
Fleming's left hand rule
Home
Demo with Motor Effect Apparatus
Home
Increasing the Size of the Force
Home
The motor effect: true or false?
Home
Single Science Only
Exam Question
Home
Single Science Only
Exam Question
Home
Coil in a Magnetic Field
Home
How does an electric motor work?
Home
Demo Motor
Home
DC electric motor simulation
Home
How do we increase motor strength?
Would the same strength motor be used in both of these?
How can the strength of an electric motor be increased?
 increase the current flowing through the coil
 increase the strength of the magnet
 increase the number of turns on the coil
Worksheet
Home
The Motor Effect
recap
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor
Home
Induction
09/04/2016
Aim:
•To observe and define induction
•To explain how electricity is generated
Home
Exam Question
Home
Exam Question
Home
Inducing current in a wire
Home
What is electromagnetic induction?
Current Carrying Wire + Magnetic field = Motion
Motion + Magnetic field = Current in Wire
Changing Magnetic field = Current in wire
If they are at right angles to each other
Home
Inducing current in a coil
Home
Induction
If a magnet is moved near a coil of wire a current is induced in the wire
•
Faster motion, bigger current
•
Stronger magnet, bigger current
•
More turns, bigger current
•
Change direction of motion, change direction of current
Home
Factors affecting induced current
Home
How can motion produce a current?
Home
What are Generators?
A generator is a device that converts mechanical energy into electrical
energy. It is the opposite of an electric motor.
Power stations use generators to produce
electricity on a large scale.
Mechanical energy is provided by rotating
turbines that can be powered by:
 high-pressure steam – in coal, oil, gas and nuclear power stations
 wind – in wind turbines
 falling water – in hydroelectric power stations
Home
How do AC generators work?
Home
AC generator simulation
Home
Induction: true or false?
Home
What is a transformer?
The voltage of an alternating current can be changed using a device
called a transformer.
A transformer contains two
coils that are wound around a
soft iron core.
iron core
The alternating current in
the primary (input) coil
produces an alternating
magnetic field.
This alternating magnetic field
induces an alternating current
in the secondary (output) coil.
primary
coil
secondary
coil
Home
How does a transformer change voltage?
The voltage induced in the secondary (output) coil depends on the
number of turns on the primary and secondary coils.
A step-up transformer has
more turns on the secondary
coil and so increases voltage.
A step-down transformer has
fewer turns on the secondary
coil and so decreases voltage.
Home
How are transformers used to supply electricity?
Home
Transformers




Transformers are used to change the voltage from the Primary
(input) to the Secondary (output)
They only work with a.c. (alternating current)
Input (Primary) Voltage
=
Output (secondary) Voltage
Number of Primary Turns
Number of Secondary Turns
Example Question:

Input voltage = 230 V

Primary turns = 10000

Secondary turns = 500

What is the secondary voltage?
Worksheet
Home
Exam Question
Exam Question Separate Science only
Home
Induction
09/04/2016
Aim:
•To observe and define induction
•To explain how electricity is generated
Home
USE ME IN THIS PRESENTATION
Home