P3 Using magnetic fields to keep things moving

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• Created by: KAustria
• Created on: 18-05-14 09:45
What is a magnetic field?
A region of space where a magnetic force acts
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What do iron fillings which loop from one pole to the other represent?
Lines of force or field lines.
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How can a magnetic field be produced with a wire?
When a current flows through a wire, a magnetic field is produced around the wire.
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How is an electromagnet made?
Wrapping an insulated wire around an iron which wll then be known as a core.
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How do you know that electromagnets produce temporary magnetism.
When a current flows through the iron it becomes strongly magnetised. When the current is switched off the iron loses its magnetism.
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Where are electromagnets used?
Scrapyard cranes, circuit breakers, electric bells and relays.
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What is the motor effect?
When a wire carrying an electric charge will experience a force when placed in a magnetic field.
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When is the force caused by the motor effect at its maximum and minimum
Maximum when the are wire an an angle of 90° to the magnetic field. Minimum when the wire is parallel to the magnetic field.
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What is used to determine the direction of the force?
Fleming's left hand rule
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What does the first (index) finger represent?
1. The magnetic field 2. The second (middle) finger represents the current 3. The thumb represents the force.
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How can the size of the force be increased?
1. Increase the strength of the magnetic field 2. Increase the size of the current.
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How can the direction of the force on the wire be reversed?
1. Direction of current is reversed 2. Direction of the magnetic field is reversed.
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In a simple electric motor, why does the coil spin?
1. A force acts on each side of the coil due to the motor effect 2. The force on one side is in the opposite direction to force on the other.
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What does a 'split-ring' commutator' do
Reverses the direction of the current around the coil every half turn. The coild is always pushed in the same direction.
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What happens when a electrical conductor 'cuts' through magnetic field lines?
A potential difference is induced across the ends of the conductor.
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What is the name given the event where a pd is induced across the ends of the coil of wire?
Electromagnetic induction.
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What happens when the polarity of the direction of movement of the wire/ coil is reversed?
The direction of the induced pd is reversed.
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What is the only conition for a pd to induced during electromagnetic induction?
If there is movement (wire).
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How do you increase the size of the induced pd in electromagnetism?
1. Increasing the speed of the magnet 2. Increasing the strength of the magnetic field 3. Increasing the number of turns on the coil
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What does a transformer consist of?
Two coils of insulated wire called the primary coil and the secondary coil.
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Explain what happens when an alternating current passes through a primary coil?
When an altenating current passes through the primary coil it produces an alternating magnetic field in the core. This field always expands and collapses.
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How does an alternating pd occur in a transformer?
The alternating magnetic fields pass through the secondary coil and produces a pd across it ends.
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Why are coils of wire in a transformer insulated?
So that the current does not short across the iron core or through the adjacent wires, but through the whole coil
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Why is the core of a transformer made out of iron?
Iron can be easily magnetised.
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What are transformers used in?
In the national grid.
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Describe the the step up transformer.
1. Makes pd across the secondary coil greater than the primary coil. 2.Done by increasing the number of turns of coil in the secondary coil.
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Describe the step down transformer
1. Makes pd across the secondary coil less than the primary coil 2. This is done by decreasing the number of turns of coil in the secondary.
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What happens if a 1.5V cell is used as the supply for the primary coil?
Nothing will happen because transformers need a supply of alternating current.
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What are the 4 main features of a switch mode transformer?
1. ferrite core 2. operates at a much higher frequency 2. Lighter and smaller 3. Uses little powere when there is no device connected across its output terminals.
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Why does the National Grid step up the pd form power stations?
The higher the pd at which the electrical energy is transmitted across, the smaller the amount of energy wasted in the cables.
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Why are step down transformers at the end of the transmission?
To reduce pd so that it is safer to use by consumers.
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How are pd across and the number of turns on the primary and secondary coils related in an equation?
Vp/Vs = np/ns
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What does the following equation represent? Vp x Ip = Vs x Is
To show how transformers are almost 100% efficient. I represent current in amperes.
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Other cards in this set

Card 2

Front

What do iron fillings which loop from one pole to the other represent?

Back

Lines of force or field lines.

Card 3

Front

How can a magnetic field be produced with a wire?

Card 4

Front

How is an electromagnet made?

Card 5

Front

How do you know that electromagnets produce temporary magnetism.