# Homework Help: Just finished my phy 2 midterm 3

1. Apr 12, 2010

### jimmybagz

Just finished my phy 2 midterm 3!!- one problem I am iffy about

1. The problem statement, all variables and given/known data
So first question I have is on a conceptual problem in our exam dealing with wavelength and frequency of light along with speed in water and Air
1. The frequency of light in water is____ that of air
2. The wavelength of light in water is____ that of air
3. The speed of light in water is ____ that of air

2. Relevant equations
$$\lambda$$matter=$$\lambda$$vaccum/n
v=c/n
v=f*$$\lambda$$

3. The attempt at a solution
1. This is the one I put my best guess on....equal to
-I was not sure on this one very frustrating as I studied hard and just didnt remember this one
2. Pretty sure....Less than
-I used the formula relating n to $$\lambda$$ and since nwater>nair therefore the wavelength in water is less than wavelength in air...I also confirmed this since i remember a salesman at a scuba/snorkeling place trying to convince me that i should buy a red lensed mask because red light is as he said "absorbed by water" well seeing as red is higher in the visible spectrum if he wasn't just blowing smoke up my rear end then wavelength of light in water must be less than that of air
3. Easy peasy lemon squeezey... less than
-nwater>nair there for vwater<vair

Last edited: Apr 12, 2010
2. Apr 12, 2010

### AtticusFinch

Re: Just finished my phy 2 midterm 3!!

You got 1 correct. Think about a wave on a string. If at the boundary between two strings of different density you have different frequencies that would mean there are times when there should be some sort of jump discontinuity between the strings. That obviously doesn't make sense.

The scuba mask story doesn't really pertain to question 2. I think divers use red tinted masks because red light is the first to be absorbed when diving. Really to answer number two you have to realize that the speed of light decreases in water and the frequency stays the same so the wavelength must decrease.

3. Apr 12, 2010

### jimmybagz

Re: Just finished my phy 2 midterm 3!!

well regardless if the scuba story is pertinent... $$\lambda$$water<$$\lambda$$air aka the answer I put is correct?

4. Apr 12, 2010

### AtticusFinch

Re: Just finished my phy 2 midterm 3!!

Yeah. That is what I said...

5. Apr 12, 2010

### jimmybagz

Re: Just finished my phy 2 midterm 3!!

cool well thanks thats what I needed