P3.3 Keeping Things Moving

HideShow resource information
  • Created by: Anisha
  • Created on: 28-04-13 12:49
Preview of P3.3 Keeping Things Moving

First 513 words of the document:

P3.3 Keeping Things Moving
Electric currents produce magnetic fields. Forces produced in magnetic fields can
be used to make things move. This is called the motor effect and is how appliances
such as the electric motor create movement. Many appliances do not use 230
volts mains electricity. Transformers are used to provide the required potential
difference.
P3.3.1 the Motor Effects
When a current flows through a wire a magnetic field is produced around the wire. Applications of
electromagnets could include their use on cranes for lifting iron/steel.
The size of the force can be increased by:
increasing the strength of the magnetic field
increasing the size of the current.
The conductor will not experience a force if it is parallel to the magnetic field.
The direction of the force is reversed if either the direction of the current or the direction of the magnetic
field is reversed.
FLEMINGS LEFT HAND RULE
P3.3.2 Transformers
If an electrical conductor `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 a potential difference is induced across the
ends of the coil. An alternating current in the primary coil produces a changing magnetic field in the iron
core and hence in the secondary coil.
This induces an alternating potential difference across the ends of the secondary coil. In a stepup
transformer the potential difference across the secondary coil is greater than the potential difference
across the primary coil. In a stepdown transformer the potential difference across the secondary coil is
less than the potential difference across the primary coil.
The potential difference across the primary and secondary coils of a transformer is related by the
equation: Vp /Vs = np/ns
Vp is the potential difference across the primary coil in volts, V
Vs is the potential difference across the secondary coil in volts, V
np is the number of turns on the primary coil
ns is the number of turns on the secondary coil
If transformers are assumed to be 100% efficient, the electrical power output would equal the electrical
power input. Vp x Ip = Vs x Is
Vp is the potential difference across the primary coil in volts, V
Ip is the current in the primary coil in amperes (amps), A
Vs is the potential difference across the secondary coil in volts, V
Is is the current in the secondary coil in amperes (amps), A
Switch mode transformers operate at a high frequency, often between 50 kHz and 200 kHz. Switch mode
transformers are much lighter and smaller than traditional transformers working from a 50 Hz mains
supply. Candidates should be aware that this makes them useful for applications such
as mobile phone chargers. Switch mode transformers use very little power when they are switched
on but no load is applied.

Comments

No comments have yet been made

Similar Physics resources:

See all Physics resources »See all resources »