Physics 3 - Electromagnetism Flashcards
Why is the wire in a coil around the core of a transformer coated in plastic?
Plastic is an insulator, preventing current flowing through the core. This prevents a short circuit.
Why is an alternating pd required for a transformer to work?
An alternating pd produces an alternating magnetic field. Transformers won’t work with a direct pd as the magnetic field lines will not change direction.
Why is the core of a transformer made of (soft) iron?
Iron is magnetic / can be magnetised.
Describe how a transformer works (Big one!)
An alternating pd or current is needed in the primary coil. This induces a changing magnetic field in the primary coil. This in turn gives a changing magnetic field in the secondary coil. This induces an alternating pd in the secondary coil.
Describe the motor effect.
A wire with a current flowing through it has a magnetic field around it. When in a permanent magnetic field, the two fields interact and a force results. A wire parallel to the permanent field lines will experience no force.
Give two ways of increasing the force in the motor effect?
Increase the current through the wire or strength of the magnet.
How is the force in the motor effect reversed?
Change the direction of the current or reverse the poles of the magnet.
Give the name of a lighter, smaller transformer than a traditional iron core transformer.
Switch mode transformer. Operating at a higher frequency.
Give two advantages of a switch mode transformer over a traditional iron core transformer.
It is lighter, it is smaller, easier to carry around and it draws little power when no load is applied.
Describe the materials that make up a transformer.
An iron core. Copper wire, wrapped in plastic (to prevent short circuit), in turns to form a coil on each side of the transformer.
What is the difference between a step up and step down transformer?
Step up - more turns of wire on the secondary coil producing a bigger pd than the input pd.Step down - less turns of wire on the secondary coil producing a smaller pd out than the one in.
Where would a switch mode transformer be found?
In a charger for mobile devices such as laptops, tablets and mobile phones.
How do you find the direction of the force in the motor effect?
Use Fleming’s left hand rule. First finger, magnetic field North to South. Second finger, the current flow. Thumb, the direction of the force. All at 90 degrees to each other.
How is a potential difference induced across a conductor (like a coil of wire).
If the electrical conductor (a coil) cuts through a magnetic field.
If the electrical power output of a transformer is the same as the input power what has been assumed?
The efficiency of the transformer is 100%. This is not true in reality as heat energy and perhaps some sound (buzzing) energy is lost to the surroundings.
