OP - What is Light? - Week 1 Flashcards
Do all photoreceptors of all eyes respond to light in the same way?
No, the spectrum at which photoreceptors can detect light is different for different species, and so they have different visible wavelength spectrums compared to humans.
What percentage of the light reaching our eyes is absorbed?
~10%
What is the minimum range number of photons needed to elicit a response, and what does this depend on?
5-14 photons needed, depending on the level of bleaching.
What is the structure of light?
It has both electrical and magnetic fields orthogonal to each other)
What is the speed of light?
3x10^8m/s
Define the following equation:
ν = c / λ
ν = frequency c = speed of light λ = wavelength
What two experiments can show light acts as both a wave and a particle?
Double slit experiment - interference patterns suggests it is a wave
Barrier experiment - shadow of the barrier is clear and straight, not fuzzy - suggests it is a particle
How do polarisers demonstrate light acts as a wave?
Monopoloraised light cannot pass through a polariser of a different orientation, whereas a particle should.
What is the photoelectric effect? Describe what happens with red light vs UV light. Does this support wave or particle theory for light?
Light of different wavelengths shone onto a smooth metal surface resulted in electron emission
Red light - No matter the intensity, never resulted in electron emission
UV light - Electron emission occurred, their energy was independent of light intensity, just high number of electrons
Not consistent with wave theories for light.
The photoelectric effect suggested what relationship between electrons in metal and photons? Describe the equation (both forms).
Light could absorb photons of light (particle) whose energy is inversely proportional to their eavelength. E = h ν or E = h c / λ E - energy h - Planck's constant c = speed of light ν = frequency λ = wavelength
What is the wavelength range for visible light, and what wavelength for each colour?
640-400 Red - 640 Orange - 590 Yellow - 575 Green - 510 Blue - 470 Violet - 400
What colour are our eyes most sensitive to?
Yellow-green
What do photopic and scotopic sensitivity curves represent?
Sensitivity to different wavelengths
Photopic - bright light
Scotopic - dim light
What is human wavelength sensitivity like compared to photosynthesis wavelength sensitivity? What do both of these sensitivities align with?
Human sensitivity is best the the yellow-green region, while photosynthesis is best on either side - the red and blue regions.
They both align well with the Sun’s emission spectrum.
Why are tungsten bulbs inefficient for lighting?
Though they emit warmer colours, a very small percentage of their photon emission is in the visible region, Majority of the emission is infrared and beyond, lost as heat.
