Electromagnetic Induction (Edexcel GCSE Combined Science: Physics): Flashcards
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State three factors that affect the size of the potential difference induced in a coil.
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State three factors that affect the size of the potential difference induced in a coil.
Any three from: the speed the magnet or coil is moved; the number of turns on the coil; the area of the coil; the strength of the magnetic field.
How does increasing the speed of movement affect the induced potential difference?
It increases the rate at which the magnetic field lines are cut, which increases the induced potential difference.
What factor determines the direction of the induced potential difference?
The orientation of the poles of the magnet (the direction it is moved).
What rule determines the direction of an induced potential difference and the magnetic field it produces?
The induced potential difference (and the resulting magnetic field) always opposes the change that produces it.
A magnet is pushed north pole first into a coil. What polarity does the near end of the coil become, and why?
It becomes a north pole, so it repels the magnet, opposing it being pushed in.
Pulling a magnet away from a coil makes the near end of the coil a ______ pole, which attracts the magnet to oppose its removal.
Pulling a magnet away from a coil makes the near end of the coil a south pole, which attracts the magnet to oppose its removal.
True or False?
Increasing the number of coils increases the induced potential difference.
False.
It is the number of turns, not the number of coils, that should increase the induced potential difference — these are not the same thing.
Define transformer.
A device that uses the generator effect to change the value of an alternating potential difference (or current); it consists of a primary coil, a secondary coil and an iron core.
Why is a transformer's core made of iron?
Iron is easily magnetised, so it lets the changing magnetic field from the primary coil pass through to the secondary coil.
Describe how a changing current in the primary coil induces a current in the secondary coil.
The alternating current in the primary coil produces a changing magnetic field, which passes through the iron core and cuts through the secondary coil, inducing an alternating potential difference (and current) at the same frequency as the primary supply.
A ______ transformer has more turns on the secondary coil than the primary coil and increases the potential difference.
A step-up transformer has more turns on the secondary coil than the primary coil and increases the potential difference.
State two uses of transformers in the supply of electricity.
Any two from: increasing the potential difference before transmission across the national grid; lowering high-voltage electricity to household voltages; lowering mains voltage in adapters for electronic devices.
True or False?
A step-down transformer has more turns on its secondary coil than its primary coil.
False.
A step-down transformer has fewer turns on the secondary coil than the primary coil, which decreases the potential difference.
Why does transmitting electricity at a high current cause energy loss?
A high current flowing through the power lines heats the wires, transferring electrical energy to heat and reducing efficiency.
Why is electricity transmitted at high voltage rather than high current?
Since P* = *IV, transmitting at a high voltage allows the same power to be delivered with a smaller current, which reduces heating and energy loss in the cables.
Define a step-up transformer.
A transformer that increases the potential difference of electricity, placed after the power station before transmission.
Define a step-down transformer.
A transformer that decreases the potential difference of electricity, placed before buildings for domestic use.
Name three roles of transformers in the supply of electricity.
Increasing the potential difference before transmission across the national grid, lowering the high voltage in power lines to the voltages used in houses, and lowering mains voltage in adapters for electronic devices.
Electricity is transmitted at ______ voltage and ______ current to reduce energy loss in the power lines.
Electricity is transmitted at high voltage and low current to reduce energy loss in the power lines.
True or False?
Step-down transformers are placed after the power station.
False.
Step-up transformers are placed after the power station; step-down transformers are placed before buildings.
Define an ideal transformer.
A transformer that is 100% efficient, so the input power equals the output power.
Why can a transformer not increase the power output of a supply?
By the law of conservation of energy, a transformer can only change the voltage and current, not increase the total power.
For a 100% efficient transformer, V~p~ × I~p~ = V~s~ × ______
For a 100% efficient transformer, V~p~ × I~p~ = V~s~ × I~s~
Write the equation linking electrical power, potential difference and current.
P* = *VI
where P is power in watts (W), V is potential difference in volts (V) and I is current in amps (A).
A transformer steps up a 100 V supply to 400 V. If the current in the primary coil is 8 A, calculate the current in the secondary coil, assuming the transformer is 100% efficient.
V~p~ × I~p~ = V~s~ × I~s~
100 × 8 = 400 × I~s~
I~s~ = 2 A
True or False?
In an ideal transformer, increasing the voltage on the secondary coil increases the current on the secondary coil.
False.
Since V~p~ × I~p~ = V~s~ × I~s~ is fixed by the input power, increasing V~s~ decreases I~s~.
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