# Franck Hertz Graph

1. Nov 27, 2013

### jenny777

Hello,

How can I determine when the current is starting rise? What methods should I use to do so? on excel or matlab.

I've attached an image of my graph below

Thanks a million

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2. Nov 27, 2013

### Jilang

Er, can you use a ruler?

3. Nov 27, 2013

### jenny777

that's what I did on my last lab, for planck's constant, but apparently I need some systematic way of determining it according to my TA

4. Nov 27, 2013

### jenny777

I'm writing a formal lab report for Franck Hertz oscillation

5. Nov 27, 2013

### Jilang

Can you plot the gradient using Excel. Then if possible say when the increase in the gradient becomes statistically significant?

6. Nov 27, 2013

### jenny777

how do I find the gradient? (sorry I'm not really good at this)

7. Nov 27, 2013

### Jilang

Or may get Excel to determine the best fit line. It will tell you the equation of the line and where is crosses the x axis.

8. Nov 27, 2013

### Jilang

If you don't know how look up trend lines in Excel help.

9. Nov 27, 2013

### jenny777

I tried fitting an exponential and linear line, but it didn't work. it was way too off. But why would the would I be looking for a y-intercept of the line? (where it crosses the origin)

10. Nov 27, 2013

### jenny777

oops, i meant to say why would I be, not why would the would I ....haha

11. Nov 27, 2013

### Jilang

Rather than plot the current, you could plot the change in the current. That would be the change in each current measurement divided by the each little change in your input variable. That would be the gradient.

12. Nov 27, 2013

### Jilang

Sorry, I meant the x axis. And you can't use all the points - you need to exclude the flat part, else you will get rubbish.

13. Nov 27, 2013

### jenny777

I think the gradient plot sounds good! thanks so much!