P4.2 Flashcards
What is the motor effect
When a current carrying wire, in a magnetic field, experiences a force
Size of force formula
Calculating Direction of force
Flemmings left Hand rule
What is a motor
An electric motor uses the motor effect to transfer electrical energy to kinetic energy.
What is a motor made from
An electric motor (in effect) consists of a loop/length of wire, with a current, in a magnetic field.
How does a motor work
- An electric motor (in effect) consists of a loop/length of wire, with a current, in a magnetic field.
- The wire will experience a force, given by F = BIL
- As current flows in opposite directions in theopposite sides of the coil, forces act in opposite directions on opposite sides of the coil, causing the coil to rotate.
- Once coil rotates fully up, the coil actually experiences NO FORCE ON ITS SIDES(as the current no longer runs perpendicular to B-field lines,) = The reason why the coil continues to move past this position is due to its momentum
- If the current stayed running in the same direction - the coil will turn anti-clockwise instead and keep flip-flopping
- Therefore, every half turn of the coil, the current direction must be reversed to ensure the coil continues to turn in the same direction.
How to increase speed of motor
must increase size of force acting, F=BIL, so…- - - increase current in coil
- increase strength of B-field/magnet
- have more loops/longer length of wire
- force is greatest at 90° and zero at 0°.
What is electromagnetic induction / generator effect
When a conductor cuts the magnetic field lines of a magnet, a potential difference is induced across the ends of the conductor
How does electromagnetic induction work
When a conductor (wire) cuts magnetic field lines, electrons are moved to one side of the conductor, creating a p.d.
If this conductor (wire) is part of a complete circuit, a current flows.
How to increase size of induced potential difference
- Increase number of coils
- Use a stronger magnet
- Move the wire quicker through the magnetic field
What is Lenz’s law
The direction of the induced p.d. is such that itopposes the change producing it.
Lenz’s Law ensures that the law of conservation of energy isn’t violated.
Example of Lenzes law in Action
If a magnet approaches a coil of wire with its north pole, the p.d. induced (current) in the coil of wire will give rise to a north pole on the end the magnet is approaching.
The north pole of the magnet and north pole of coil will then repel, opposing the motion inducing the p.d.
How does an alternator work
- A rectangular coil is made to spin in a uniform magnetic field.
- The coil is connected to a meter by metal brushes that press on two metal commutator rings.- SLIP RINGS
- As the coil turns, each side of it cuts the field lines from below, then above and so on.
- The induced potential difference is therefore repeatedly changing direction (and so therefore is the induced current).
How to increase size of p.d in an alternator
- Rotating coil faster
2. Using a stronger magnet3. Using a coil with a larger surface area/more turns
The faster the coil rotates in an alternator
… the greater the rate of cutting field lines… the greater the peak value of induced p.d.… AND the greater the frequency of the induced p.d.
What is a dynamo
direct current generator.
How does a dynamo work
- A rectangular coil is made to spin in a uniform magnetic field.
- The coil is connected to a meter by a SPLIT RING COMMUTATOR
- reconnects the coil the other way round every half turn of the coil
- The induced potential difference is therefore in the same direction
Compare and alternator and a dynamo
Both use coils and magnets to induce a p.d. (and current).
Alternators use commutator slip-rings to give rise to an a.c. current.
Dynamos use split-ring commutators to give rise to a d.c. current.
What are transformers
are devices that use an alternating p.d. (current) in a primary circuit to induce an alternating p.d. (current) in a secondary circuit.