prelim

• What is a transverse wave?

  A wave where particles vibrate at 90° to the wave direction
• What is a longitudinal wave?

  A wave where particles vibrate in the same direction as the wave
• What is the formula for wave speed?

  $v =$$f \times \lambda$
• What does frequency measure?

  Number of waves per second
• What is diffraction?

  The bending of waves around a barrier
• How can diffraction be increased?

  By increasing the wavelength or decreasing the gap
• If four complete waves are produced in 0.40 s, what is the frequency?

  10 Hz
• Calculate the speed of waves if frequency is 10 Hz and wavelength is 0.5 m.

  $v =$$5 \text{ m/s}$
• What is the speed of electromagnetic waves?

  $3 \times 10^8 \text{ m/s}$
• What is a detector for radio waves?

  Ariel
• How do you calculate the distance using time delay and speed?

  $d =$$v \times t$
• If there is a 4 μs delay, what is the distance to the helicopter?

  600 m
• What happens to light when it enters a denser material?

  It slows down and bends towards the normal
• What is ionising radiation?

  Removal or addition of an electron from an atom
• What is half-life?

  Time for activity to decrease by half
• What is the purpose of shielding in radiation safety?

  To protect from harmful radiation exposure
• How do you calculate absorbed dose?

  $D =$$\frac{E}{m}$
• If a person receives 0.7 J of gamma radiation, what is the absorbed dose for 75 kg?

  $0.009 \text{ Gy}$
• How do you calculate total equivalent dose?

  $H_{total} =$$H_{gamma} +$$H_{alpha}$
• What is the formula for average speed?

  Average speed = Total distance / Total time
• What is the difference between distance and displacement?

  Distance is scalar; displacement is vector
• How do you calculate acceleration?

  $a =$$\frac{v - u}{t}$
• What is the formula for displacement in a velocity-time graph?

  Displacement = Area under the graph
• How does Newton's Third Law relate to balanced and unbalanced forces?

  Every action has an equal and opposite reaction
• What is the formula for weight?

  $W =$$m \times g$
• What increases friction?

  Increasing surface area and mass
• What is the unit of activity in radiation?

  Becquerel (Bq)
• Why is background radiation measured before experiments?

  To subtract it from the results
• How do you determine the half-life from activity data?

  Measure count at intervals and subtract background
• Why is a gamma source preferred as a medical tracer?

  It is the most penetrative type of radiation
• What is the annual effective dose limit for the public in the UK?

  1 mSv
• If the initial activity is 200 kBq and after 12 years it is 25 kBq, what is the half-life?

  4 years
• What is the annual effective dose limit for radiation workers in the UK?

  20 mSv
• What is the role of neutrons in nuclear fission?

  They collide with uranium nuclei to create reactions
• How does nuclear fusion differ from nuclear fission?

  Fusion combines nuclei; fission splits them
• What is the charge of a gamma ray?

  No charge
• What is the charge of an alpha particle?

  Positive charge
• What is the charge of a beta particle?

  Negative charge
• What is the significance of equivalent dose?

  Indicates biological harm of radiation
• What are natural sources of background radiation?

  Cosmic rays, rocks, radon gas