## Problem A9

$c=\lambda v$

Jasmin Argueta 1K
Posts: 69
Joined: Fri Sep 28, 2018 12:16 am

### Problem A9

In the seventh edition problem A9 I am having trouble solving for the frequency for 2.5nm . I tried using using the equation h(wavelength)v=c. I just rearagned it and did v=c/h. So I did v=(2.998x10^8)/2.5. The book says the answer is 1.2x10^17 HZ. I'm not sure how, do you covert 2.5 nm to meters, if yes I still don't understand where the 17 exponent came from since we're diving the exponents(subtracting in reality).

Sofia Ban
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

### Re: Problem A9

First, use the equation c=wavelength x frequency(v). Rearrange this equation so that you are looking for the value of v, so v= c/wavelength. Then, convert nm to m. We know that the SI unit for nm is 1x10^-9m, so 2.5nm will be 2.5x10^-9m. Plug in this value as well as the speed of light constant (3.00x10^8), and you should get 1.2 x10^17 as your numerical value.

keyaluo4C
Posts: 54
Joined: Fri Sep 28, 2018 12:17 am

### Re: Problem A9

Yes, you would first have to convert nm to m which would make it v=(3x10^8 ms^-1)/(2.5x10^-9 m).

Michael Torres 4I
Posts: 92
Joined: Thu May 10, 2018 3:00 am
Been upvoted: 1 time

### Re: Problem A9

To find the frequency for 2.5 nm use the equation (speed of light)=(wavelength)(frequency).

You can start off by converting the wavelength to meters so you're using proper SI units. You need to do this because you're also using the speed of light in meters.

Next, arrange the equation as (speed of light)/(wavelength)=(frequency).

(2.998 * 10^8 m/s)/(2.5 * 10^-9 m) = 1.2 * 10^17 s^-1

This makes frequency equal to 1.2 * 10^17 Hz.

You get the 17 exponent because 8 - (-9) = 17.

Pritish Patil 1K
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

### Re: Problem A9

The trick is to first convert 2.5nm to 2.5x10^-9 meters (SI unit). Then plug into the rearranged equation of v=c/lambda to solve for the frequency.

Jasmin Argueta 1K
Posts: 69
Joined: Fri Sep 28, 2018 12:16 am

### Re: Problem A9

Thank you everyone!