## What is equation is this ?

jordanginyard_
Posts: 62
Joined: Wed Sep 30, 2020 9:43 pm

### What is equation is this ?

What formula is c = 3.00 x 10^8 m.s^-1 for. I remember seeing this in the lecture but I was confused about why we use this equation or do we even use it at all.

Darlene Lien 3E
Posts: 80
Joined: Wed Sep 30, 2020 9:37 pm

### Re: What is equation is this ?

c= 3.00x10^8 m/s is the speed of light. In the lecture today, it was used to derive the de Broglie equation.

Melis Kasaba 2B
Posts: 61
Joined: Wed Sep 30, 2020 9:49 pm

### Re: What is equation is this ?

C represents the speed of light, which is 3.00 x 10^8 m/s. For light, wavelength (λ), frequency (ƒ), and velocity (v) can all be measured and they fit the equation for waves, where v is velocity or the speed of light (c). So c is used in the equation c = λƒ = 3.00 x 10^8 m/s. This equation can be rearranged to find wavelength: λ = c/ƒ and also c is used in this energy equation: E = (hc)/λ. In today's lecture, Lavelle used c to derive the de Broglie equation.
Last edited by Melis Kasaba 2B on Mon Oct 19, 2020 12:51 pm, edited 1 time in total.

Samantha Pedersen 2K
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### Re: What is equation is this ?

c = 3.00 x 10^8 m.s^-1 is the speed of light. We often use it in the equation $c = \lambda \nu$ where $\lambda$
is the wavelength and $\nu$ is the frequency. For example, if you are given the frequency of a wave and you want to calculate the wavelength, you can divide the speed of light (3.00 x 10^8) by the frequency. If you are given the wavelength and you want to find the frequency, you can divide the speed of light by the wavelength.

Inderpal Singh 2L
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### Re: What is equation is this ?

This is the equation for the speed of light. It is used a lot in the equations revolving around the photoelectric effect :)

Sharon Kim 2A
Posts: 63
Joined: Wed Sep 30, 2020 9:42 pm

### Re: What is equation is this ?

The speed of light equation (c = lambda * frequency) was used to derive the De Broglie equation. With that equation, it was derived by the combination of Energy = pc and E = hv. The speed of light equation was rearranged to be v = c/wavelength. From E=hv (substituting v), we get E=hc/wavelength. Make that equal to E=pc, the speed of light constant cancels out which finalizes the De Broglie formula, wavelength=h/p.

Ariel Guan 1H
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### Re: What is equation is this ?

c is the speed of light. It is used in the c=λv equation (v is frequency), however, the equation is often rearranged in terms of frequency and substituted into E=hv. The equation would then be E= (hc)/λ .

905290504
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### Re: What is equation is this ?

c is the speed of light ina vacuum

Aydin Karatas 1F
Posts: 77
Joined: Wed Sep 30, 2020 9:37 pm

### Re: What is equation is this ?

c is the constant for the speed of light in a vacuum. It is used to relate the wavelength and frequency of EM waves with the equation c = (wavelength)v.

In today's lecture, c is used in the derivation for De Broglie's equation:

Since E = hc/(wavelength) and E = pc
hc/(wavelength) = pc ---> wavelength = h/p = h/mv

Hope this helps.

Eileen Quach Dis 2A
Posts: 111
Joined: Wed Sep 30, 2020 9:49 pm

### Re: What is equation is this ?

c represents the speed of light in a vacuum. We plug in this value to the equation c= wavelength * v, where v represents the frequency. Knowing the speed of light, you can use this equation when you know the wavelength and you want to solve for the frequency of the light, or vice versa. Since you know the speed of light, you can also use this equation by isolating v and substituting the value that it's equal to into the equation, E=hv, depending on what the question is asking.

Kimiya Aframian IB
Posts: 81
Joined: Wed Sep 30, 2020 9:34 pm

### Re: What is equation is this ?

jordanginyard_ wrote:What formula is c = 3.00 x 10^8 m.s^-1 for. I remember seeing this in the lecture but I was confused about why we use this equation or do we even use it at all.

Hi! "c" represents the speed of light which is a constant that we use in many different equations that involve electromagnetic waves. This also means that we can use this constant even if the light is not necessarily visual light. From our equations, c can help solve for Energy of photons, wavelength, frequency, etc.
Hope this helps!

Malakai Espinosa 3E
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### Re: What is equation is this ?

The number you listed is an estimated value for the speed of light! Some people round to three while others use more specific values like 2.98. I believe Professor Lavelle is okay with us rounding to 3 though.