•Modified
example: Hailstorm (with your car
outside in it)
–Threshold
for damage to car set by size of individual hailstones
•Below
threshold hailstones cause no dents
•Above
threshold they cause bigger dents
–Number
of dents = number of hailstones bigger than threshold
–Very
unlikely two small hailstones can hit exactly together to cause dent
–
•Real
life example: Ultra-Violet light
hitting your skin
–Threshold
for chemical damage set by energy (wavelength) of photons
•Below
threshold (long wavelengths) energy too weak to cause chemical changes
•Above
threshold (short wavelength) energy
photons can break apart DNA molecules
–Number
of molecules damaged = number of photons above threshold
–Very
unlikely two photons can hit exactly together to cause damage