Exam Questions

• Explain the ideal properties of a radioactive source for use in medical diagnosis (4)

  • short half-life means less damage to cells
  • low ionizing power means less damage to cells
  • highly penetrating means it can be detected outside the body
  • emits gamma radiation
• Explain why the radiation source inside the smoke alarm should have a long half-life (2)

  • short half life means the count rate decreases quickly
  • until 1.3 half-lives the count rate is above 80 per second
• Explain how the paths of the alpha particles were used to develop the nuclear model of the atom (4)

  • most alpha particles pass straight through the atom
  • which shows that the atom is mostly empty space
  • very few alpha particles are deflected through a large angle
  • which shows the atom contains a nucleus where the mass/charge of the atom is concentrated
• Explain how the distance at which an electron orbits the nucleus may be changed (3)

  • electron may absorb EM radiation
  • and move further from the nucleus
  • to a higher energy level
• Explain how the risk from internal contamination is different to the risk from external irradiation by a source of alpha radiation. (5)

  • alpha radiation has low penetrating power
  • so externally will be stopped by skin
  • alpha radiation has high ionizing power, so if injected into the body, it will be absorbed by tissues
  • internal contamination will cause a greater risk of harm to cells
• Explain why a spark jumps between the negatively charged rod and the earthed conductor. (3)

  • large potential difference between the objects
  • causes electrons to move through the air
  • from rod to conductor
• Explain why the reading on the balance increases when a charged rod is held above. (3)

  • additional force acting downwards
  • as rod is negatively charged
  • and like charges repel
• A student rubbed a plastic rod with a cloth.

  The rod became negatively charged and the clot became positively charged.

  Explain why the clot became positively charged. (3)

  • electrons transferred from cloth to rod
  • electrons are negatively charged
  • so more positive charges than negative charges on rod
• As the person moves down the zip wire her increase in kinetic energy is less than her decrease in gravitational potential energy.

  Explain why. (2)

  • work done against friction
  • causes thermal energy to be transferred to the surroundings
• Different people have different speeds at the end of the zip wire.

  Explain why (2)

  • people have different surface areas
  • so they would be affected by air resistance differently
• The negatively charged student touches a metal tap and receives an electric shock.

  Explain why (3)

  • p.d between student and tap
  • electrons transferred from hand to tap
  • which earths the charge
• Some carpets have thin copper wires running through them. The student is less likely to receive an electric shock after walking on this type of carpet.

  Suggest why (2)

  • copper has low resistance
  • smaller p.d between student and tap
• The maximum speed of this cyclist can travel on a level road is 14m/s.

  How does cycling uphill affect the maximum speed of this cyclist?

  Explain why. (3)

  • maximum speed decreases
  • maximum power output of cyclist is constant
  • but additional work is done against gravity
• The internal energy of the air increases as the tyre is inflated.

  Explain why (2)

  • work is done on the air
  • so the temperature increases
• The power output of the turbine is directly proportional to the kinetic energy of the air passing the blades each second.

  Describe the effect on the power output when the wind speed is halved. (3)

  • mass of air is halved, kinetic energy decreases by factor of two
  • wind speed halved so kinetic energy decreases by factor of four
  • so kinetic energy decreases by a factor of 8