Download P3.3 keeping things moving checklist File

P3.3 Keeping things moving
  
Can you…?
P3.3.1 The motor effect
State that a magnetic field is produced around a wire when a current flows
through it
Give examples of applications of electromagnets, such as cranes for lifting
iron/steel
Describe the principle of the motor effect and its use in any given situation
Outline how the motor effect creates movement in electric motors
Explain two ways that the size of the force can be increased
State that a conductor will not experience a force if its is parallel to the magnetic
field
Identify the direction of the force using Fleming’s left-hand rule
State that the direction of the force is reversed if either the direction of the
current or the direction of the magnetic field is reversed
Interpret diagrams of electromagnetic appliances in order to explain how they
work
P3.3.2 Transformers
Describe how a potential difference is induced across the ends of an electrical
conductor when it ‘cuts’ through a magnetic field
Describe how a potential difference is induced across the ends of a coil if a magnet
is moved into a coil of wire
Outline the basic structure of a transformer
Outline how an alternating current in the primary coil produces a changing
magnetic field in the iron core and hence in the secondary coil, which in turn
induces an alternating potential difference across the ends of the secondary coil
Compare the potential difference across the primary and secondary coils in stepup and in step-down transformers
Relate the potential difference across the primary
p
 p
and secondary coils of a transformer using the
equation:
s
s
Relate electrical power input and output for
 p  s s
p
tranformers, assuming they are 100% efficient, using
the equation:
State that switch mode transformers operate at a high frequency, often between
50 kHz and 200 kHz
Explain the advantages of switch mode transformers working from a 50 Hz mains
supply in terms of size and weight, and why this makes them useful for
applications such as mobile phone chargers
State that switch mode transformers use very little power when they are switched
on but no load is applied
Compare the use of different types of transformer for a particular application.
Examples might include mobile phones chargers and power supplies for laptops
V n
V n
V I V I