inverse square law

• what is irradiance a measure of

  the amount of light which falls on a surface every second
• equation for irradiance

  I = P/A
• what is irradiance measure in

  watts per square metre
• irradiance decreases as distance from the source increases
• what is a point source

  a source that irradiates equally in all directions: like a lamp
• explain why the irradiance decreases when the distance from a point source of light increases (2)

  I=P/A

  power stays the same

  area increases
• what should be kept constant in an experiment to verify the inverse square law?

  supply voltage

  type of bulb used

  background light
• irradiance is inversely proportional to distance squared
• A student wishes to carry out an experiment to confirm the inverse square law associated with irradiance. They are given a range of light sources to work with. Which light source is the most appropriate for their experiment?

  • fluorescent tube
  • LED
  • torch bulb
  • regular light bulb

  torch bulb