# Do you fancy argon-ion lasers?

1. Nov 29, 2009

### LebLlama

Do you fancy argon-ion lasers??

I sure dont. =/

1. The problem statement, all variables and given/known data
I dont. This is a practice test problem and I cannot figure it out. Frustrating!

An argon-ion laser emits a blue-green beam of light with a wavelength of 488 nm in a vacuum. What is the difference in energy in joules between the two energy states for the atomic transition that produces this light?

a.
6.18 × 10–20 J

b.
1.05 × 10–20 J

c.
5.10 × 10–28 J

d.
4.08 × 10–19 J

e.
4.76 × 10–24 J

2. Relevant equations

See below. Im not sure its right though since im not producing one of the multiple choice questions.

3. The attempt at a solution

This is what I came up with so far:
so we know the wavelength (l) of the light emitted.

now, E (energy) is h * n (h = Plancks constant, n = frequency)

so

E = h * n

but also, l = c T = c / n (T is the period of the oscillation of the emitted light) which means

n = c / l

so

E = h * c / l

with this formula E can be computed

(c = 3 * 10^8 m/s is the speed of light)
my answer isnt any of the above, however. :(

help? =)

2. Nov 30, 2009

### ideasrule

Re: Do you fancy argon-ion lasers??

Try again. The formula E=hc/l is right, and if you plug in the right numbers, it DOES give you one of the answer choices.

3. Nov 30, 2009

### LebLlama

Re: Do you fancy argon-ion lasers??

I keep getting 4.07 x 10^-28

Thats a combination of c and d haha. :(

4. Nov 30, 2009

### LebLlama

Re: Do you fancy argon-ion lasers??