Exam questuions

• The student connects the foil to a signal generator providing an alternating current at 40 Hz. 

  Explain why the aluminium foil emits a low pitched humming noise when connected to the signal generator. 

  current carrying aluminium foil has a magnetic field

  magnetic field of foil interacts with the magnetic field of the magnet

  force experienced by foil (as predicted by Fleming's left hand rule)

  (alternating current causes the) direction of force to alternate every half cycle

  causing the foil to vibrate/oscillate

  (the vibrating foil causes the) air molecules to vibrate/oscillate

  the movement of the air molecules produces the pressure variations in the air needed for a sound wave
• When a sound wave is incident on the diaphragm, it causes a current to be induced in the coil. 

  Explain why a current is induced in the coil when a sound wave is incident on the diaphragm. (4)

  • (the sound wave causes the) diaphragm to vibrate

      allow oscillate for vibrate

  • (causing the moving) coil to vibrate

         allow oscillate for vibrate

  • coil cuts the magnetic field of the magnet  

  OR  coil passes through the magnetic field of the magnet

  • inducing a current in the coil  

  OR  induces a potential difference across the ends of the coil
• During this stage, the star is stable. 

  Explain why the star is stable during this stage of its evolution. (3)

  gravitational pull inwards

  outwards force due to fusion reactions

  both forces are in equilibrium
• Describe the evolution of a star with a mass similar to our Sun.  (6)

  cloud of gas OR nebula OR cloud of hydrogen

  pulled together due to the force of gravity to form a protostar

  hydrogen nuclei fuse to form helium

  and the star becomes a main sequence star

  when hydrogen begins to run out, star cools and expands to become a red giant

  outer layers of red giant are dissipated to leave a hot dense core known as a white dwarf