User:Arianna Pregenzer-Wenzler/Notebook/Junior Lab/2008/10/01
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Set UpSJK 01:49, 22 October 2008 (EDT)
We are using a mecury light source shining through a lens that focuses and splits the 'white light' into it's spectrum. By moving the lens on its support rods (all the way out) we focused the first maxima on the slit in the h/e apperatus. We decided to measure the bands of light to the right of the first maxima. The first three bands are shades of blue that we will call Blue 1,2,3 then a yellow/green band and a orange band. The first part of this experiment is compareing the time to reach the stopping potential (Vmax) for the five different band varying the intensity of the light using filters that allow between 100% down to 20% of the light to pass. For the 3 blue bands we just use the filter to change the intensity, for the orange and yellow bands we need to add the apropriate colored filter.
For each intensity we wait until our volt meter has reached a steady(ish) max value that we call the max for that intensity. Then we make 5 timed trials of the time needed to reach this Vmax, making sure we reset the apperatus between trials. We need to do this for only two bands of color!!
Data, Experiment 1
part A note pushing reset button can result in moving the h/e apperatus.
moving from center maxmia to the right we start w/ blue 1 , then blue 2, blue 3 , yellow/green, orange
note all readings V/20,this is not correct, the 20 on the voltmeter corresponds to how precisely the voltmeter is mesuring the voltage, ie how many decimal places are being reported.
This time I am going to start with the intensity at 20%, measure the Max stopping potential, then measure the time it takes to get to that stopping potential for all the other intensities. Ok this was frustrating, I started here with the idea of taking another set of measurments on the time it takes to reach a stoping potential set by taking the stoping potential of the green band at its lowest intensity. I made the assumption that if I could reach a given potential at 20% intensity, then I could reach that same potential at 40% and greater intensities. Wrong assumption, the potential I reached at 20% intensity, was greater than what seemed to be the Max potential at 40% so just to check I moved to 60% and 100% I should have recorded the potential's I did reach but I didn't think to, but they weren't easily comming up on the potential reached at 20%.
we hooked up the oscilliscope so we could see the patter of the voltage. We thought we should see the voltage go from zero to some max voltage in an exponitial fassion. We spent quite awhile with the oacilliscope set to AC coupling (should have been set to DC). On AC coupling we saw a voltage occilating around zero with a spike right after we zeroed the insterment, decaying exponetially back to zero, not what we wanted to see (this didn't make any sense). With the coupling se to DC, you see a voltage of zero (as the insturment zeros), once you release the button there is a spike of positive voltage toward (appearing to reach) the max voltage then the voltage drops and then approaches Vmax in the expected exponitial fassion. The voltage reaches its max value very quickly (a second or so) so trying to measure the time to reach Vmax in the first experiment was pretty much pointless.
record DVM voltage for each band
I am going to assume this is the (aprox Max) voltage for each color
remember to divide Voltage by 20 (our Voltmeter is set on 20)
I am recording the values the voltmeter fluxuates between
making sure to zero out the instrument using the discharge, and waiting to record my value until the voltmeter reading is fluxuating in a constant manner
1st Blue:2.059-2.060 Volts this is a medium blue
2nd Blue:1.720-1.721 Volts this is a purple blue
3rd Blue:1.497-1.498 Volts this is a bright blue
making sure to use the yellow filter, I adjusted to light so that it fell on the slit/photodiod then put the filter in front of the slit then zeroed the insturment
Green:0.839-0.840 Volts (with yellow filter) this is a bright yellow/green,
I have a yellow and a green filter and I'm thinking that this value shoud be intrupreted as green so....
Green:0.852-0.853 Volts (with green filter)
Orange:0.714-0.715 Volts (with yellow filter) this is just orange
Data Analysis Experiment I
Data Analysis Experiment II
Data, Experiment 2
For each band of color in the first order measure stoping potential, then move to second order and repeat
Starting at the center maxima (a 'white' band) moved to the lst order to the right. Note these values should be the same as the values I recorded for Part B of experiment B, if they are different this points to systematic error (our equiptment is giving different values for what should be the same reading). I am noticing that this time through the values given by the voltmeter are not fluxuating between values.
Blue 1: 2.053 Volts
Blue 2: 1.713 Volts
Blue 3: 1.487 Volts
Green: 0.850 Volts (using green filter)
Orange: 0.716 Volts ( using yellow filter)
2nd Order (trial 1):
Blue 1: 2.049-2.050 Volts
Blue 2: 1.715-1.716 Volts
Blue 3: 1.510-1.511 Volts
Green: 1.235-1.236 Volts (using green filter)
Orange: 0.801-0.802 Volts ( using yellow filter)
note I did not ecpect these values for 2nd order, I expected that the stopping potential would decrease, of course there are plenty of variables, like the amount of light in the room. But I am taking these measurments one after another so the conditions should be similar for all trials.
2nd Order(trial 2):
Blue 1: 2.039-2.040 Volts
Blue 2: 1.708-1.709 Volts
Blue 3: 1.510-1.511 Volts
Green: 1.232-1.233 Volts (using green filter)
Orange: 0.803-0.804Volts ( using yellow filter)
note: there is a lot of variation here, I will go to record a value that I think has stablized only to re-check myself and find that my voltmeter is fluxuating between a slightly different set of values.