Photo Electric Effect - Making Sense of Data

1407 Words3 Pages

Photo Electric Effect - Making Sense of Data

Brief:

I took part in a class experiment on the photo-electric effect. We

gathered lots of results which can be used to calculate several

values, such as the value of Planck's Constant. My task is to make

sense of the data obtained by interpreting, analysing and manipulating

the data from this class experiment. We did four repeats obtaining

results from six different colour bands. I have to communicate my

results logically, using ICT where appropriate.

Apparatus:

In the class experiment we used a unit developed by the University of

Newcastle-upon-Tyne and Rutherford College to provide a simple method

of calculating Planck's Constant. I can't expect a high order of

accuracy, due to the inexpensive production process. It analyses

different energy levels over the range of the visible spectrum by

using different coloured filters between the light source of the

photo-tube. The reverse voltage is controlled by a large knob on the

front of the unit. The knob is made to be large so that a higher level

of accuracy can be achieved.

[IMAGE]

How the Photo-Electric Effect is Recorded:

[IMAGE]

The voltage produced by the photoelectric tube is linked to an

electro-ray oscilloscope. It is measured by applying a voltage against

that produced by the photoelectric tube until the reading on the

oscilloscope is flat, then the reverse voltage is measured on the

voltmeter. The reverse voltage is controlled by the variable voltage

supply as shown on the diagram above. The Reason that the p.d is read

on the volt meter is because through use the variable voltage supply

may be...

... middle of paper ...

... but less than half the

value it should have been. This could have been caused by several

major sources of error:

* Varying Sensitivity Over the Spectral Range. This is why the

results plotted on the graph are not in a perfect straight line.

* Small amounts of photo-emissive material landing on the anode

during the production process. This causes reverse emission,

reducing the accuracy of the value of the reverse voltage.

* A small red slit in the red filter. This allowed light of higher

energy level through, raising the p.d produced by photo-emission

slightly raising the value of the stopping potential for the red

wavelength. This would have changed the line of best fit of the

graph slightly, creating further inaccuracy in the calculated

value of Planck's Constant.

Open Document