Harvey's Question Thread

[HarveyD]

ohh okay, that would make sense
i'll have a look through the assessor reports and check that out, thanks

what did you end up getting for the graph one?

[Lasercookie]

ohh okay, that would make sense
i'll have a look through the assessor reports and check that out, thanks

what did you end up getting for the graph one?

It says it at the start of the VCAA 2007 report.

With the graph question:
Ek_max is the stopping voltage in electron volts. But volts and electron volts are interchangeable right?
So stopping voltage is a measure of energy, so it make sense to use e=hf.

But then I tried to confirm the answer: the frequency of the stopping voltage would be the threshold frequency right?
so , so that implies that

Extrapolating the graph should give a good approximation of the work function. Like counting the squares, it's a bit dodgy I think, but VCAA gave this as a legit method in VCAA 2007... anyway Work function should be about 2 using that method? and the threshold frequency (2.66 * 10^14 Hz) should be the x-int. It doesn't seem to match up.

[HarveyD]

hmm this was my method
Ek Max = hf - W
1.1 ev = hf - 2
hf = 3.1 ev
then f = 7.5 x 10^14 Hz

so i thought maybe the answers made a mistake and found the threshold frequency rather than the actual frequency used...
hmm 

[Lasercookie]

so i thought maybe the answers made a mistake and found the threshold frequency rather than the actual frequency used...
hmm 

Yeah, I did your method to start off with, but I'm pretty sure we are looking for the threshold frequency. f1' was the frequency they used when measuring the stopping voltage.

Wait, I made a common sense error (i think). The scale is stopping voltage vs. frequency, so the threshold frequency wouldn't be the x-intercept. If it was the x-int, that would mean a 0 stopping voltage i.e. no electron ejected.

I'm starting to go around in circles now. I think I'll leave this question for now and ask my teacher when school starts again.

[HarveyD]

Are the solutions to this question right..?
I thought only intensity affected  the photocurrent?