# measuring angle of light refraction through a prism

Hoping someone can point me in the right direction. I am trying to measure the angle of light refraction through a prism (labeled as "base" in the diagram below) that is filled with a liquid. I will not know the refractive index of the liquid. See this diagram:

The biggest hurdle I am encountering is how do I measure "X" with a sensor? Basically the location the laser hits the back wall. I will already know "L", and with "X" it is simple trigonometry to figure out the angle.

Any ideas? Thanks in advance!

How about a phototransistor on an arm that you move out on a rail and use an Arduino to determine when the sensor crosses the laser beam path?

How accurately do you need to measure X and over what range? Both in terms of angle and distance.

Another idea similar to Crossroads' would be to mount a mirror on a servo motor to reflect the beam back to a phototransistor at a fixed point. The Arduino would vary the angle of the mirror until the beam was detected.

A more advanced solution would be to use a linear CCD strip salvaged from an old scanner. That involves knowing how to drive it which is an advanced skill. It involves finding and reading the data sheet for the CCD and getting the Arduino to generate those pulses.

I will already know "L",

Will you now? That is a good trick measuring to a point that does not physically exist.

What about measuring it with a ruler ?
But I presume this is an exercise from your physics class, and there are some stipulations which you haven't mentioned here.

What about measuring it with a ruler ?

What like Obama, or Putin?
I think a rule would be a better bet.

Hi,
Place the laser sensor inline with the laser.
Place the prism on a platform on an encoder shaft.
With no prism note the encoder output, place prism on turntable, and turn until laser beam coming out of the prism, hits sensor.
Note encoder reading, using previous reading calculate angle turned.
Encoder may put the cost of procedure out of reach.

Tom....

I think a rule would be a better bet.

In American English, a ruler is used to measure distances.

A rule is more like a law.

jremington:
In American English, a ruler is used to measure distances.

Thank God I am not an American then.

And yet "ruler" originated in Middle English.

"1.
a person who rules or governs; sovereign.
2.
Also, rule. a strip of wood, metal, or other material having a straightedge and usually marked off in inches or centimeters, used for drawing lines, measuring, etc."

In American English it is also correct to say that "the colonists rejected taxation by the British ruler", but not correct to say that President Obama is a ruler.

...Middle English.

Back then, most people outside the Shire spoke Elvish. The only Elvish I know is "You ain't noth'n but a hound dog..."

Anyway, we seem to have refracted away from the subject!

Anyway, we seem to have refracted away from the subject!

We are just looking at it from a different angle.

I'll get me coat.