Transcript Electricity - Island Physics

Electromagnetism
•Syllabus
•Lesson 01 – The Motor Effect
•Lesson 02 – Induction
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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
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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).
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The Motor Effect
16/07/2015
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor
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Fields Bar Magnets
Single Science Only
handout
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Opposite Poles
Single Science Only
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Same Poles
Single Science Only
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Fields due to Current
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Single Science Only
Single Coil of Wire
Solenoid
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Magnetic Field Lines
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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
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Wire in a magnetic field
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The Catapult (Motor) Effect
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Motor Effect
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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
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Fleming's left hand rule
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Demo with Motor Effect Apparatus
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Increasing the Size of the Force
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The motor effect: true or false?
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Single Science Only
Exam Question
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Single Science Only
Exam Question
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Coil in a Magnetic Field
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How does an electric motor work?
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Demo Motor
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DC electric motor simulation
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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
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The Motor Effect
recap
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor
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Induction
16/07/2015
Aim:
•To observe and define induction
•To explain how electricity is generated
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Exam Question
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Exam Question
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Inducing current in a wire
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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
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Inducing current in a coil
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Induction
If a magnet is moved near a coil of wire a current is induced in the wire
•
Faster motion, bigger current
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Stronger magnet, bigger current
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More turns, bigger current
•
Change direction of motion, change direction of current
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Factors affecting induced current
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How can motion produce a current?
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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
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How do AC generators work?
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AC generator simulation
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Induction: true or false?
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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
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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.
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How are transformers used to supply electricity?
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Transformers
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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:
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Input voltage = 230 V
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Primary turns = 10000
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Secondary turns = 500
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What is the secondary voltage?
Worksheet
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Exam Question
Exam Question Separate Science only
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Induction
16/07/2015
Aim:
•To observe and define induction
•To explain how electricity is generated
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USE ME IN THIS PRESENTATION
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