Inverse Variations

[Guest]

I am having some trouble with inverse variations, I would appreciate any sort of help.

The frequency of a radio wave varies inversely as its wavelength. If a 200 meter wave has a frequency of 3000 kilocycles, what is the wavelength of a wave that has a frequency of 2000 kilocycles?

y=k/x
200 = 3000/x
Then cross multiply to get 200x = 3000 and x = 15

Then take 2000/15 = 133.33

I'm not sure that I am getting the numbers in the right locations.

Thanks.

 

[skeeter]

let's not use x and y ...

let f = frequency in kilocycles
w = wavelength in meters

frequency varies inversely as its wavelength ...

f = k/w where k is the constant of proportionality

200 meter wave has a frequency of 3000 kilocycles ...

3000 = k/200

k = 600000

so, your final equation is ...

f = 600000/w

can you now find the wavelength of a 2000 kilocycle wave?

 

[wjm11]

a 200 meter wave has a frequency of 3000 kilocycles

Just as an aside, these inputs do not correspond to real world physics. For electromagnetic radiation, wavelength*frequency = the speed of light (about 3.00x10^8 m/s), which is what the "k" in this problem should be. This problem seems to indicate a speed of light of twice that value.