Keeping things moving Flashcards
When current flows through a wire what is produced around the wire?
A magnetic field.
What can we use to work out the direction of a force of the motor effect?
Fleming’s left hand rule.
Size of the force on a wire can be increased by:
Increasing the strength of the magnetic field.
Increasing the size of the current.
True or false, in the motor effect a conductor will not experience force when it is perpendicular to the magnetic field.
False, the conductor will not experience force when it is parallel to the magnetic field.
The direction of force on a wire carrying current in a magnetic field is reversed when?
If either the direction of current or direction of magnetic field is reversed.
What happens if an electrical current ‘cuts’ through a magnetic field?
A potential difference is induced across the ends of the conductor.
If a magnet is moved into a coil of wire what happens?
A potential difference is induced across the ends of the coil.
How does a transformer work?
An alternating current in the primary coil produces a changing magnetic field in the iron core which induces an alternating potential difference in the secondary coil.
In a step-up transformer, what can be said about the potential differences of the coils?
The potential difference across the secondary coil is greater than the potential difference across the primary coil.
In a step-down transformer, what can be said about the potential differences of the coils?
The potential difference across the primary coil is greater than the potential difference across the secondary coil.
Potential differences of the primary and secondary coils are related by the equation:
Vp / Vs = np / ns
Where:
Vp is potential difference across primary coil in V.
Vs is potential difference across secondary coil in V.
np is number of turns on the primary coil.
ns is number of turns on the secondary coil.
If the transformer is assumed to be 100% efficient, what can be said about the power input and output?
They can be said to be equal through the equation:
Vp x Ip = Vs x Is
Where:
Vp is potential difference across primary coil in V.
Vs is potential difference across secondary coil in V.
Ip is current in primary coil in A.
Is is current in secondary coil in A.
Switch mode transformers often operate at what frequencies?
Between 50kHz and 200kHz.
Switch mode transformers are much what than traditional transformers?
Lighter and smaller.
Switch mode transformers that are much lighter and smaller operate from what supply?
50Hz main supply.
