PD5 COMMUNICATIONS REVISION TOPICS

The Following topics are the MAIN areas of study for this unit for both Foundation and higher level candidates. It is advised that these areas should be revised in more depth.

    AREAS OF STUDY
    Magnetism and Electromagnetism
    Motors
    Generators
    AC and DC Current
    Distribution of Electricity
    Kinetic and Potential energy
    Gravity
    Work Done
    Power
    Efficiency

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1) MAGNETISM AND ELECTROMAGNETS
  1. Magnetic Materials (Iron, Nickel and Colbolt )
  2. Magnetic field (how to detect it)
    Iron filings showing the magnetic fielda plotting compass can also be used to show the magnetic field lines
  3. Direction of a magnetic field (North to South)
  4. Making a Magnet (Stroking, passing a DC Current through a wire wrapped around the material)
  5. Destroying a magnet (hitting, heating passing ac through a wire wrapped around it)
    Any wire carrying a current produces a magnetic fieldElectromagnet you can make the field stronger by increasing the number turns OR Increasing the current

    Uses of electromagnets

    Elecric Bell Motor
    Also used for:
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    2)MOTORS

    Click here for a detailed description of how a DC motor works

    Putting an electromagnet near fixed permanent magnets makes the electromagnet (coil) move. This is the principal of a motor

    Flemings Left Hand Rule

    Flemings LEFT hand rule. (to work out direction wire moves)

    Parts of a motor

    model motor
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    3)GENERATORS

    Opposite of a motor. Moving a magnet near a coil generates an electrical current as shown here Electromagnetic inductionThe same effect can be achieved if the coil is moved towards the magnet

    To work out the direction of the induced current Use Flemings RIGHT hand rule (to work out the direction of the current) Flemings right hand rule

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    4)AC AND DC CURRENT

    Click here for details of how a generator makes AC

    AC-Alternating current the sort of current you get from the mains (looks like sine wave)

    DC Direct current- the sort you get from batteries (flat line)
    AC and DC Current

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    5)DISTRIBUTION OF ELECTRICITY( The National grid)
  1. Power station

    2. Power station
  2. National grid

    3. The National grid systemSimplified National Grid

  3. Transformers
Click here for more information on how transformers work
These are devices that increase (or decrease) Voltage
Decrease Voltage = Step Down Transformer Increase Voltage = Step Up Transformer e.g
step down transformer
There will be 6 turns on the secondary coil (since 75v is 5 times 15v, the Primary coil will also have 5 times more turns)

Only works on an a.c current

Primary coil current(amps) ¸ Secondary coil current (amps) = number of primary turns¸ number of secondary turns
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    6) POTENTIAL AND KINETIC ENERGY
    Potential Energy = Mass × Gravity × Height
    pe = m × g × h
    (j) = (kg) (N/kg) (m)

    What happens when an object falls?-

    How the Energy of a falling object changesAs the Object falls it gains Kinetic energy at expense of Potential energy

    Kinetic Energy = ( Mass × Velocity˛ ) ÷ 2
    k.e = ( m × v˛ ) ÷ 2
    (J) (kg) m/s)
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  1. Acceleration of free fall (10m/s2 on Earth)
  2. Terminal velocity (top speed of an object when falling)


  3. Force that keeps planets in orbit
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Work is done whenever a force moves an object over a distance

Work Done = Force × Distance
WD = F × D
(J) or Nm (N) (m)

Energy Formula

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Rate at which WORK is done

Power = Work Done ÷ Time
P = WD ÷ t
(w)or J/s) (J)) (sec)

Mechanical Power Formula

NB J/s is also a valid unit
1 watt = 1 J/s
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How much of the Energy put in is converted into USEFUL Energy

Efficiency = USEFUL Energy Out ÷ Energy In
Eff = Eout ÷ Ein
no units (J)) (J)

Efficiency Formula

energy flow diagram

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