Calculating e/m Ratio: A Puzzling Problem

• barcelonaboy
In summary: I'm not sure where else I might be going wrong, but if you have any other pointers that might be useful I would be grateful.
barcelonaboy
I'm trying to calculate the ratio of e/m, I've plotted the given data points to get a straight line graph with a gradient of 0.848.

I know that the ratio of e/m is given by e/m = (4.49*10^8 * gradient^2)/volts
where volts = 3000.

When I plug the numbers in I get a value of 107625 which is nowhere near the given book value of e/m 1.7*10^11 Ckg^-1

I think that I'm doing something in the wrong units as I need to get the answer in C/kg^-1, but I can't see where I'm going wrong.

Any pointers owuld be much appreciated

I'm afraid that I don't know what you might be doing wrong because I don't know what data varibles you have. Are you plotting a current against a radius of a circle, or velocity against current flow, or voltage against current even I think can be one setup for an electron beam experiment.

Have you checked that your units are in the SI format?

Is your set of axis the right way round?

Haths

Hi Haths,

I'm plotting a graph of Voltage (V) against Current (mA) (V/mA) as part of an electron beam experiment, which is giving a gradient of 0.848 with the R^2 coming out as 0.9991 which is a good fit for the data points, so I'm confident in the graph and the data points.

The equation that I need to plug my numbers into is, this includes the 4.49*10^8 as a dimensionless constant

I think that I'm going wrong on the units in the gradient as I can't see how to get from an equation that has units in volts and mA to one that involves Coulombs/kg or if there is some conversion factor that I'm not aware of.

What is the purpose of calculating e/m ratio?

The e/m ratio is used to determine the charge-to-mass ratio of an electron, which is a fundamental physical constant that is important in various areas of physics and engineering.

How is e/m ratio calculated?

The e/m ratio is calculated by measuring the deflection of an electron beam in a magnetic field and using the principles of electromagnetism to determine the ratio of the electron's charge to its mass.

Why is calculating e/m ratio considered a "puzzling problem"?

The e/m ratio has historically been a challenging measurement to make accurately, as it requires precise control and measurement of both electric and magnetic fields. Additionally, the value of the e/m ratio has been a topic of debate and has been revised multiple times as measurement techniques have improved.

What factors can affect the accuracy of e/m ratio calculations?

External factors such as temperature, air pressure, and magnetic interference can affect the accuracy of e/m ratio calculations. Additionally, imperfections in the equipment or experimental setup can also introduce errors in the measurement.

What are some real-world applications of e/m ratio calculations?

The e/m ratio is used in particle accelerators, mass spectrometers, and in the design of electronic devices such as cathode ray tubes and vacuum tubes. It is also important in understanding the behavior of charged particles in various fields, such as in space exploration and plasma physics.

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