p6 exam questions

• X-rays have been used in medical imaging for many years to see the internal structures of patient's bodies.

  
  

  explain why the doctor leaves the room but the patient is safe to have the X-ray. 3/3

  high exposure to x-rays can lead to cell mutations OR cancer (1)

  the patient has very few x-rays per year so they have very low exposure (1)

  the doctor would have a very high exposure if they stayed in the room for every x-ray (1)
• An X-ray film is initially white. when X-rays are absorbed by the film it turns black. Explain why the bones appear white but other areas appear darker. 2/2

  X-rays are able to penetrate tissue and be absorbed by the film (1)

  X-rays are absorbed by the bone, leaving the film white in these areas (1)
• the frequency of the x-rays used is 2.5 x 10^18 Hz. the speed of light is 3 x 10^8 m/s. calculate the wavelength of the x-ray used. 3/3

  equation: waves speed = frequency x wavelength (1)

  rearrangement: wavelength = waves speed/frequency (1)

  substitution and correct evaluation: (1)

  wavelength = 3x10^8/2.5x10^18

  = 1.2 x 10^-10 m
• explain why microwaves are suitable for cooking food

  microwaves are able to penetrate (1-2cm) into food (1)

  microwaves are absorbed by water molecules in the food (1)

  ...causing them to vibrate and heat up the food (1)