Electric Motors + Transformers Flashcards
What are motors used for?
Many electrical appliances that make things move.
What is there around a wire carrying electric current?
A circular magnetic field.
What is an electromagnet?
If the wire is made into a coil, the magnetic field pattern becomes similar of that of a bar magnet.
What is the motor effect?
When a current flows in a wire that is in a magnetic field, the wire experiences a force: if wire is free to move, it moves.
When is the force largest?
When the current is at right angles to the magnetic field lines: direction of force is always at right angles to both the current in the wire and the magnetic field lines.
When is no force experienced?
When the current is parallel to the magnetic field lines.
When is the direction of the force reversed?
If either the current or the magnetic field is reversed.
What happens when a simple motor is placed in a uniform magnetic field?
One side of the rectangular current-carrying coil is forced upwards: the other is forced downwards to produce rotation.
When will the motor turn faster?
- if current is increased
- number of turns of coil is increased
- magnetic field is stronger
- soft iron core in the coil.
Why does the motor effect work?
Because the interaction between the magnetic field around the current carrying wire and the magnetic field of the permanent magnets.
What does the commutator do?
Connects the coil of the motor to the power supply: swaps contacts with the coil every half turn to reverse the current though the coil: keeps motor turning.
What does a transformer do?
Changes the voltage of an a.c power supply.
What does a transformer consist of?
Two separate coils around an iron core.
What is fed into the primary coil?
The input voltage.
What is across the secondly coil?
The output voltage.
What does a step up transformer do?
Converts a low voltage input to a higher voltage output: primary coil has fewer turns than the secondary coil.
What does the step down transformer do?
Converts a high voltage input to a lower voltage output: primary coil has more turns than the secondary coil.
What does the alternating current in the primary coil create?
An alternating magnetic field around it: magnetic, soft iron core channels the magnetic field though the secondary coil.
When is the alternating voltage induced across the secondary coil?
When the alternating magnetic field will continuously cut through the wires in the secondary coil.
What happens if the number of turns in the secondary coil is doubled?
The output voltage will be doubled to.
The turns ratio is equal to the voltage ratio: word equation:
Voltage across primary coil/voltage across secondary coil = number of turns in primary coil/number of turns in secondary coil.
