Im having a very difficult time solving a question regarding the mass of an elec
ID: 1446605 • Letter: I
Question
Im having a very difficult time solving a question regarding the mass of an electron and the lab we just completed.
1a. Would it be possible to use the earths magnetic field to deflect the beam?
1b. How large would the tube have to be?
2. Assuming the earth had no magnetic field, would it be practical to determine the mass of the electron by accelerating it horizontally through a known potential difference and subsequently observing its deflection in the earths gravitation field. How far would it have to go?
I was told in order to solve this i need to find the velocity of an electron, but Im unsure which equations to use.
Explanation / Answer
Answer 1 a:
No, we cannot use the earths magnetic field to deflect the beam.
Magnetic poles always come in pairs, equal and opposite: if a field attracts an N pole, it repels the attached S pole. Similarly, if we generate the field by a current in a loop of wire --say, shaped like a rectangle--for each side in which the current flows in one direction, there exists a side where it flows in the opposite direction, and the magnetic field exerts opposite forces of equal strength on the two sides.
The magnetic field is very weak. Compared to fields in electric machinery, where appreciable forces are exerted, it is a few thousand times weaker.
1(b) The tube need not be large enough
2)
yes,it is possible to accelerate the electron.There are three circuits that need to be connected: filament heater supplying VF, accelerating potential VA , which accelerate the electrons emitted from the heated cathode to the carbon target. The external bias ( 0-50 V) focuses the electron beam and allows for the diffraction pattern to be visible at lower accelerating potential.
with the help of the de Broiglie equation we shall write an expression for the electron wavelength as a function of the accelerating voltage Va . This expression should contain several known constants, the wavelength and Va . On the next step: using the condition for the 1st interference maximum (2) , or better – the small angle approximation (3), write an expression that will connect the electron wavelength to something that you can measure ( the ring diameter D). relation between D and va is determined.Through this we can find that a calculation using de Broglie’s equation shows that electrons accelerated through a potential difference of 4 kV have a wavelength of about 0.02 nm. Interference and diffraction effects, as studied in physical optics, demonstrate the existence of wave.