Light: Energy, Wavelength, Frequency and Planck's Constant
Light travels in tiny packages called photons. Each of these photons carries are certain amount of energy, E. Based on this, we also say that they have a wavelength (λ) and a frequency (ν), and that the three of these are related as follows:
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c = λν
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E = hν
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where c is the speed of light (3.0 x 10^8 m/s) and h is Planck's constant (6.626 x 10^-34 Js).
Wavelength is measured in distance. It is usually best to convert it to metres.
Frequency is often given in hertz (Hz). These are the opposite of seconds (s^-1).
Energy is often given in joules. This is ideal. If it is given in calories, you must convert is to joules by multiplying by 4.184
Wavelength is measured in distance. It is usually best to convert it to metres.
Frequency is often given in hertz (Hz). These are the opposite of seconds (s^-1).
Energy is often given in joules. This is ideal. If it is given in calories, you must convert is to joules by multiplying by 4.184
Sample Question
Q: What is the wavelength (in nm) of light with a frequency of 4.5 x 10^14 Hz?
A: c = λν, so λ = c/ν. λ = (3.0 x 10^8 m/s) / (4.5 x 10^14 s^-1) = 6.67 x 10^-7 m = 667 nm.
A: c = λν, so λ = c/ν. λ = (3.0 x 10^8 m/s) / (4.5 x 10^14 s^-1) = 6.67 x 10^-7 m = 667 nm.