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c=f lambda

I was doing a question on bitesize and got stuck with the units:
Calculate the wavelength of a photon with a frequency 5.43x10^14 Hz. I used wavelenth=c/f, and got 5.52x10^-7. The answer said the units were nm, but I thought it was just m as c is given in metres/second?:confused:
Original post by lambda98
I was doing a question on bitesize and got stuck with the units:
Calculate the wavelength of a photon with a frequency 5.43x10^14 Hz. I used wavelenth=c/f, and got 5.52x10^-7. The answer said the units were nm, but I thought it was just m as c is given in metres/second?:confused:


Unless the question specifically tells you to give your answer in nm, you're correct. However, the wavelength of small waves (particularly visible light, UV and IR) are often given in nm so you need to know how to convert between m and nm.
Original post by lambda98
I was doing a question on bitesize and got stuck with the units:
Calculate the wavelength of a photon with a frequency 5.43x10^14 Hz. I used wavelenth=c/f, and got 5.52x10^-7. The answer said the units were nm, but I thought it was just m as c is given in metres/second?:confused:
Unless the question specifically asks you to state the answer in a given unit, then as long as you state the units for that answer you actually give, you will be awarded full marks.

For instance, all of these would be correct for your answer:

5.52x10-7m

552x10-9m

552 nm

0.552x10-6m

0.552 um

Physicists and engineers round the exponential to the nearest power of 3 multiple, which makes estimating answers by hand easier and reduces potential estimating errors.
(edited 9 years ago)
Original post by lambda98
I was doing a question on bitesize and got stuck with the units:
Calculate the wavelength of a photon with a frequency 5.43x10^14 Hz. I used wavelenth=c/f, and got 5.52x10^-7. The answer said the units were nm, but I thought it was just m as c is given in metres/second?:confused:


What is the problem? nm is the unit for the visible light which is used to determine the wavelength. And the decimal power of this unit is 10^-9 what you get when you convert the value after putting the frequency and the light speed in the formula:

5.52 * 10^-7 m = 552 * 10^-9 m = 552 nm.
(edited 9 years ago)

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