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Kamal98

1. accelerating voltage and radius formed by the electron beam

2. magnetic field strength and radius formed by electron beam

Theoretically I should obtain an equation of the form:

r = (1/B) *sqrt(2mV/e)

where B is the magnetic field strength, V is the accelerating voltage and e and m the charge and mass of an electron. However after doing the experiment and plotting the graphs I get a y-intercept in the graph equation which should not be there.

I am trying to explain the reason for the intercepts. The graphs are in the link below:

https://drive.google.com/open?id=0B1PHDJFDQLRldjNYUmZ4b1pSMVk

Now, firstly the error on the value for r (the radius) is enough to explain the intercepts. Drawing graphs at the extreme ends of the error bars shows that the y-intercepts varies from a positive value to a negative value meaning that the intercept becomes zero at some point between the error bars. However I was wondering if this could also be explained through the earth's magnetic field strength. In the experiment, the apparatus has to be aligned in the earth's north-south direction, a dip needle is then used to determine the dip angle and the apparatus is elevated to the angle to cancel out the effects of the earth's magnetic field. This is important as it affects the trajectory of the electrons. However, I did not do this in my experiment. So it is a source of error. But I do not know how to determine the impact of this and whether it will be larger or smaller than the error already present on r.

I can in a way justify that taking this into account would have made the graphs more 'ideal' correcting the intercepts to near zero. But its not concrete.

Another thing:

The earth's magnetic field strength is of the order 10^-5T and the magnetic field strength in my experiment was made through helmholtz coils and the field strength varied from an order of 10^-4T to 10^-3T. Is the order of the earth's field big enough to impact the field created by the coils?

Can anyone enlighten me on this? I know its not a straightforward answer.