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### Photoelectric Post Assessment Module 30C

Posted: Fri Oct 13, 2017 3:11 pm
For 30C, to find the frequency, do we have to use the equation where Energy of the photon = (Threshold energy)(kinetic energy)?

### Re: Photoelectric Post Assessment Module 30C

Posted: Fri Oct 13, 2017 6:59 pm
you can use the equation

frequency= (.5 x mass of electron x velocity of electron squared +work function) /plancks constant

i got that from
Energy of photon - work function = kinetic energy of electron
energy of photon = h x frequency
and
KE = .5mv^2

### Re: Photoelectric Post Assessment Module 30C

Posted: Sun Oct 15, 2017 1:39 pm
For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get

frequency= (1/2mv^2 + threshold)/ h (Planck's constant)

Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging into the calculator.

You should get 6.78 x 10^14 Hz.

Hope this helps!

PS work out the "combined equation" since this it might sound confusing

### Re: Photoelectric Post Assessment Module 30C

Posted: Sun Oct 15, 2017 5:03 pm
Cassandra Mullen 3E wrote:For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get

frequency= (1/2mv^2 + threshold)/ h (Planck's constant)

Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging into the calculator.

You should get 6.78 x 10^14 Hz.

Hope this helps!

PS work out the "combined equation" since this it might sound confusing

I did the same thing, but ended up with B, 2.27 * 10^38... What did you use as the "threshold"? I added the kinetic energy to the work function, which is what I assume the threshold is, but could the threshold possibly be something else, or did I make a mistake elsewhere?

### Re: Photoelectric Post Assessment Module 30C

Posted: Tue Oct 17, 2017 1:29 pm
JonathanLam1G wrote:
Cassandra Mullen 3E wrote:For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get

frequency= (1/2mv^2 + threshold)/ h (Planck's constant)

Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging into the calculator.

You should get 6.78 x 10^14 Hz.

Hope this helps!

PS work out the "combined equation" since this it might sound confusing

I did the same thing, but ended up with B, 2.27 * 10^38... What did you use as the "threshold"? I added the kinetic energy to the work function, which is what I assume the threshold is, but could the threshold possibly be something else, or did I make a mistake elsewhere?

For the threshold/work function value, I used 2.50 x 10^-19 J.