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Physical significance 
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#1
May2008, 06:45 PM

P: 17

Can some help me to solve this question
I have no idea where to start a) What is the physical significance of the intercept of the graph with the frequency axis (xaxis)? b) What is the physical significance of the intercept of the graph with the kinetic energy axis (yaxis)? c) Use the graph to determine the value of Planck’s constant d) In a similar experiment, the cathode of the photocell is replaced with a cathode that has a stronger force of attraction for its electrons. Describe how a graph of kinetic energy against frequency would be i. Similar to the given graph ii. Different from the given graph 


#2
May2108, 02:48 AM

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Sci Advisor
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P: 9,781

If you have no idea where to start, them I'm afraid we cannot help you. You must have some idea of how to start. Have you read your class notes/text on the subject matter?



#3
Jan710, 06:35 PM

P: 31

E=hf therefore, h=E/f So referring to the graph, at 3 eV (4.8 x 10^19 J) the f is 10 x 10^14 Hz h = 4.8 x 10^19 J / 10 x 10^14 Hz h = 4.8 x 10^34 Js This does not make sense as Planck's constant, as we know, is 6.63 x 10^34 Js Can anyone shed some light on these issues? Thanks! 


#4
Jan710, 06:41 PM

HW Helper
P: 2,323

Physical significance
E does not equal hf; it equals hfW, where W is the work function of the metal.
I think parts a and b are pretty clear. The equation of the line in the graph is E=hfW, so what do the intercepts represent? 


#5
Jan710, 06:51 PM

P: 31




#6
Jan710, 07:42 PM

HW Helper
P: 2,323

There IS a yintercept. It's negative and doesn't represent an actual electron, but it does have physical significance.
Again, look at the equation of the line: E=hfW 


#7
Jan710, 07:56 PM

P: 31

h is constant, and f cannot be a negative With f=0, the yaxis will be negative the value of the work function So does the yintercept represent the work function? (in the negative plane of course) 


#9
Jan1110, 02:58 PM

P: 31

Perfect. So how would I prove Planck's constant without knowing the exact work function? Should I just use the value for W from the graph? Because it would be close but not exact...



#10
Mar110, 04:13 PM

P: 1

i would looooove to know the answer to c) & d). i figured out a) & b)!!!



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