Experiment to determine the speed of light

In summary, the speaker is trying to calculate the speed of light for their advanced physics coursework using Maxwell's equation. They planned to calculate the values for magnetic permeability and electric permittivity and use them in the equation, but their experiment is not going as planned. They are having trouble finding the value for Eo using parallel plate capacitors and varying the distance between plates. Similarly, they are unsure of how to calculate the magnetic permeability using a helmholtz coil and a magnetic sensor. The speaker is also questioning whether they should be getting an actual value for the constants or just checking their accuracy in using them. They are advised that they are simply checking their accuracy in using the predefined constants and that their results will only check their
  • #1
Stoooooart
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For my advanced physics coursework i am calculating the speed of light, one of my experiments uses Maxwell's equation for electromagnetic waves c = 1/((sqrroot of)EoxUo)

what i had planned to do was calculate values for the magnetic permeability and the electric permittivity and plug them into that equation to find the speed of light and it's not going as i planned...

to find the electric permittivity my experiment was using parallel plate capacitors, varying the distance between the plates and measuring the resulting charge between the plates, keeping the voltage constant, but i don't know how i use my results to find the value for Eo, I've tried plotting a graph of Q(charge) against 1/d(distance between plates), 1/d used to get a direct proportion, and finding the gradient of that line, but it's not giving me anything like the true value for Eo...please help?

Also, for calculating Uo, i got together a helmholtz coil and a magnetic sensor(which produces a voltage and 1V = 100mT), for that experiment i varied the current through the helmholtz coil and took not of the voltage and correspoding Teslas, but i do not know what to do with my results to calculate the magnetic permeability of free space...please help?

thanks in advance for any helpful posts.
 
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  • #2
You can't measure epsilonzero or muzero by your experiments.
muzero is a defined number, used to define the ampere in terms of the force between two wires. If you measure amps with an ammeter, you have already chosen muzero to be
4pi times 10^-7.
If you use SI units for Q and V, you have already put in the connection between epsilonzero, muzero, and the now defined speed of light.
Your results will just check your accuracy in using these already defined constants.
 
  • #3
by checking my accuracy in using these already defined constants, do you mean i should get a value for the constant and be able to check it's accuracy against the true value or do you mean check my accuracy in putting the constant to use?:S

if you mean actually deriving a value for the constants that i could check the accuracy of against the true value, what would i do to determine this value?
 
  • #4
sorry...i get what you mean now, the voltmeter and coulometer i am using in my experiments have been calibrated using these predefined constants, so in trying to calculate them, i am in short, checking my accuracy in using them...but if i am checking my accuracy of using them, should i not get an actual value to check against the true value?
 
  • #5
But you are only checking how accurately you measured.
It is like measuring the the "fundamental constant" 2.54 cm/inches
by measuring the length of a meter stick using a one foot ruler.
You are just measuring your accuracy in putting the constant to use.
If using the standard formula for capacitance, and measuring Q and V, doesn't agree with the formula, it might be that d is too large.
You need d^2<<A for the formula to hold.
Also, Q is difficult to measure accurately.
In any event though, you are just testing your accuracy of measurement.
 

1. What is the purpose of an experiment to determine the speed of light?

The purpose of this experiment is to accurately measure the speed of light, which is a fundamental constant in physics. It can also help us to better understand the behavior of light and its interactions with matter.

2. How is the speed of light typically measured in this experiment?

The most common method is using a device called a Michelson interferometer, which involves splitting a beam of light and measuring the time it takes for the beams to recombine. The distance between the two mirrors in the device is known, so by measuring the time it takes for the beams to travel this distance, we can calculate the speed of light.

3. What are some factors that can affect the accuracy of the experiment?

Some factors that can affect the accuracy of the experiment include the temperature and pressure of the medium through which the light is traveling, as well as any imperfections in the equipment used to measure the time and distance. It is important to control these variables as much as possible in order to obtain reliable results.

4. How has the speed of light been historically measured?

In the past, scientists have used various methods to measure the speed of light, including using rotating mirrors and observing the timing of eclipses of Jupiter's moons. However, the most accurate and widely accepted value for the speed of light was determined by the Michelson-Morley experiment in the late 19th century.

5. Why is it important to continue conducting experiments to determine the speed of light?

Despite many successful experiments and a well-established value for the speed of light, there is still ongoing research and experimentation being done to better understand this fundamental constant. This can lead to new discoveries and advancements in fields such as optics, astronomy, and telecommunications.

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