Speed in a Vacuum


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Sean1F
Posts: 19
Joined: Sat Sep 07, 2019 12:16 am

Speed in a Vacuum

Postby Sean1F » Sat Oct 12, 2019 1:01 pm

When is the speed in a vacuum used? Does anybody have any broad examples of when it is used?

Alice Chang 2H
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

Re: Speed in a Vacuum

Postby Alice Chang 2H » Sat Oct 12, 2019 1:26 pm

Speed in a vacuum is defined as c= 3.00*10^8 m/s, which is a constant while measuring other speeds/variables in the electromagnetic spectrum topic.
A formula given from the lecture is , which is (the speed of light) = (wavelength) x (frequency). You can use the speed of light, a constant, to find the wavelength of light, for example.

Here's the example given in the lecture (paraphrased):
3.61*10^-19 J is required to remove 1 electron without kinetic energy, what is the longest wavelength of light that can do this?
Answer:
and , so replace v in to be , which is then to find lambda (which is wavelength of light). Then, plug in numbers to get (6.626 x 10^34 Js)(3.00 x 10^8 m/s)/(3.61 x 10^-19 J) = 551 nm (wavelength of light to remove 1 electron without kinetic energy)


This is a mess to explain online, but hope this helps somehow!

Sean1F
Posts: 19
Joined: Sat Sep 07, 2019 12:16 am

Re: Speed in a Vacuum

Postby Sean1F » Sat Oct 12, 2019 2:02 pm

Alice Chang 4B wrote:Speed in a vacuum is defined as c= 3.00*10^8 m/s, which is a constant while measuring other speeds/variables in the electromagnetic spectrum topic.
A formula given from the lecture is , which is (the speed of light) = (wavelength) x (frequency). You can use the speed of light, a constant, to find the wavelength of light, for example.

Here's the example given in the lecture (paraphrased):
3.61*10^-19 J is required to remove 1 electron without kinetic energy, what is the longest wavelength of light that can do this?
Answer:
and , so replace v in to be , which is then to find lambda (which is wavelength of light). Then, plug in numbers to get (6.626 x 10^34 Js)(3.00 x 10^8 m/s)/(3.61 x 10^-19 J) = 551 nm (wavelength of light to remove 1 electron without kinetic energy)


This is a mess to explain online, but hope this helps somehow!

Thanks!
This helps a lot! :D


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