AQA Physics 9-1 Electromagnetism

  1. Which parts of a magnet are the places where the magnetic field is strongest?
    poles
  2. What do unlike poles of a magnet do?
    repel
  3. What do like poles of a magnet do?
    attract
  4. Is the magnetic force an example of a contact or non-contact force?
    non-contact
  5. What do we call something that becomes a magnet only when placed within a magnetic field?
    induced magnet
  6. What effect does induced magnetism have?


    A) Always attracts
  7. What is a magnetic field?
    An area where a magnetic material experiences a force
  8. What is the direction of all magnetic fields?
    North to south
  9. What can be used to plot the magnetic field around a magnet?
    A plotting compass
  10. Why does a compass needle point North?
    A compass needle is small bar magnet which aligns itself with the earth's magnetic field
  11. How does the magnetic field around a bar magnet change as you get further away from the magnet?
    It gets weaker (shown by field lines becoming further apart)
  12. What does the strength of the magnetic field around a current-carrying wire depend upon?
    • The current flowing through the wire
    • The distance away from the wire
  13. Use two words to describe the field within a solenoid
    • strong
    • uniform
  14. Draw the magnetic field around a bar magnet
    Image Upload 1
  15. How can the magnetic field strength around a solenoid be increased?
    • More turns
    • Increased current
    • Add an iron core
    • Put the coils closer together
  16. Draw the magnetic field around a wire carrying a current
    Image Upload 2
  17. What rule is used to determine the direction of the field around a current-carrying wire?
    • Right-hand grip
    • Image Upload 3
  18. Draw the magnetic field around a solenoid
    Image Upload 4
  19. Higher Only
    Name the effect whereby a current-carrying wire experiences a force when placed inside a magnetic field.
    motor effect
  20. Higher Only
    Name the effect whereby moving a wire within a magnetic field induces a p.d. across the ends of the wire
    Generator effect
  21. What rule do we use to determine the direction of the motor effect.
    • Flemings left-hand rule 
    • (remember, we motor on the left in the UK)
    • Image Upload 5
  22. Name the three things that affect the size of the force on a current-carrying wire placed within a magnetic field
    • Magnetic field strength
    • Length of wire (in field)
    • Current

    (F = BIL)
  23. What is the unit of magnetic flux density (B)?
    Tesla (T)
  24. Higher only
    Name a device, other than a motor, that relies on the motor effect.
    • (moving coil) loudspeaker
    • headphones
  25. Higher only
    Name a device, other than a generator, that uses the generator effect
    microphone
  26. Higher only
    When a current is induced using the generator effect, the current causes its own magnetic field. What is the direction of this field?
    • The direction of the induced field is such as it opposes the change that created it.
    • eg in the example below, a N pole will be created nearest the magnet to repel the N pole being pushed in.
    • Image Upload 6 Image Upload 7
  27. Higher only
    If an alternator coil is rotated at 30 rotations per second, what is the frequency of the induced a.c. p.d.?
    30 Hz - the frequency of the induced p.d. is the same as the frequency of rotation
  28. Higher only
    Generator effect - how can the direction of the induced current be reversed?
    • Any one of :
    • reverse magnetic field
    • reverse direction of movement/rotation
  29. Higher only
    Generator effect - how can the size of the induced current be increased?
    • Any of:
    • stronger magnetic field
    • more turns
    • rotate faster
  30. Higher only
    Which type of generator produces d.c. ?
    dynamo
  31. Higher only
    Which type of generator produces a.c. ?
    alternator
  32. Higher only
    Which type of generator uses a split-ring commutator?
    dynamo (for d.c.)
  33. Higher only
    Name the device that converts
    pressure variations in sound waves
    into
    variations in current in electrical circuits
    microphone
  34. Higher only
    Name the key parts of a transformer
    • primary coil
    • secondary coil
    • iron core
  35. Higher only
    Why is iron used as the iron core in a transformer?
    It is easily magnetised (and demagnetised)
  36. Higher only
    If a transformer has 10 times as many turns on the secondary coil as the primary, which relationship will be true:



    B) Vs = 10 x Vp and Is= Ip /10
  37. Higher only
    Describe how transformers work
    1. The alternating current in the primary coil produces an alternating magnetic field

    2. The alternating magnetic field is linked (guided) by the iron core into the secondary coil

    3. The alternating magnetic field induces an alternating p.d. across the ends of the secondary coil
  38. Higher only
    Why don't transformers work with d.c.?
    To induce a p.d. across the secondary coil the magnetic field needs to be changing. 

    If the primary coil had d.c. passing through it, a constant magnetic field would be produced.
Author
SilcoatesScience
ID
345681
Card Set
AQA Physics 9-1 Electromagnetism
Description
AQA Physics 9-1 Electromagnetism
Updated