1. Mar 16, 2004

meawinner

Here are two questions I am stuck on:
1. How many visible photons are produced per second from a 2Watt lamp? It says the range of the wavelengths is near 5x10^-7m. I tried this and got 3.33x10^33Hz but apparently thats wrong so please help me.

2. A photon of frequency 6x10^14Hz explores a path 6m long. Find the time of travel and the number of rotations of the phasor. This one I dont have a clu how to start but if I get the first answer I can easily work out the number of rotations of the phasor.

meawinner

2. Mar 16, 2004

outandbeyond2004

Mea, do you know the energy of each photon is given by Planck's constant times the frequency?

2 Watts is power = energy per second.

3. Mar 16, 2004

meawinner

Yup

Yeah i tried this and thats where i got the 3.33blah blah blah.... answer. I used 2W = 2joules per second and therefore if its one second it 2 joules, i put this in E=hf and it came out wrong as thats not the answer in my text book. Dont say why cant i just copy it because the teacher will know if there is no working. But thanks anyway. Do you know any other way?

4. Mar 16, 2004

Staff: Mentor

Re: Yup

Try again. First find the energy of a single photon, using E =hf. (Hint: First change the given wavelength into frequency, using the wave equation: v = f&lambda;.)