Physics Assessment #26

[LuminousTruth]

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The beam splitter in figure 1 is set at what angle to the incident beam?
A) 15
B) 30
C) 45
D) 60

The answer is "C". I read the explanation but I was still confused in how they got the answer.Can anyone explain?

I know that the incident beam reflects as the same angle as the returning beam but I did not know why some parts of the incident beam were initially reflected to the viewing space, since should reach the reflector array first and then come back and get reflected.

 

[Eastfolding]

This is Snell's Law, Angle of incidence = Angle of reflection.

The question tells you that the light is reflected at a right angle.

So if the angle between the incident beam and the reflected beam is 90 degrees, then the angle of incidence must be 45 degrees, because it is measured from a vector normal to the mirror.

 

[sciencebooks]

Using the diagram, the beam splitter is set at a position to create "equal distances" or "equal angles". I then figured that they must both be 45 to create 90 degrees total. I probably got really lucky after reading that other response.

 

[Trayshawn]

Was this in a passage? Or a really long discrete lol.

Its a pretty confusing diagram, but i got it now.

The light makes essentially travels in a straight line from source to reflector (it refracts in glass, but then essentially undoes that refraction when it returns to air). It reflects off the reflector in the exact same direction as it came (the angle of incidence on the reflector is zero, so the reflected light has an angle of zero as well and travels straight back). It hits the beam splitter and reflects and a 45 degree angle, right? This action should EXACTLY mirror the first reflection of light (from the source to the splitter) since none of the incident angles changed. Thus the angle of that reflection must be 45 degrees also. If the angle from the light to the normal line is 45 (the definition of an incident angle of 45 degrees) then the angle from the light to the splitter must also be 45 degrees since the angle from the splitter to its normal line (or any surface to its normal line for that matter) must equal 90.

This was a REALLY wierd problem and pretty time consuming!

 

[circulus vitios]

Was this in a passage? Or a really long discrete lol.

Its a pretty confusing diagram, but i got it now.

The light makes essentially travels in a straight line from source to reflector (it refracts in glass, but then essentially undoes that refraction when it returns to air). It reflects off the reflector in the exact same direction as it came (the angle of incidence on the reflector is zero, so the reflected light has an angle of zero as well and travels straight back). It hits the beam splitter and reflects and a 45 degree angle, right? This action should EXACTLY mirror the first reflection of light (from the source to the splitter) since none of the incident angles changed. Thus the angle of that reflection must be 45 degrees also. If the angle from the light to the normal line is 45 (the definition of an incident angle of 45 degrees) then the angle from the light to the splitter must also be 45 degrees since the angle from the splitter to its normal line (or any surface to its normal line for that matter) must equal 90.

This was a REALLY wierd problem and pretty time consuming!

I'm not understanding how you got this?

 

[richkaj]

The beam splitter is at an angle if you could think of the slab as flat you can see that the light comes in and bounces off. If you put a normal line through it, you will see that it is a complete internal reflection, equal on both sides which is 45 degrees...

 

[Trayshawn]

ahhh its so hard to explain. Its such an involved problem.

The reflections are essentially mirror images of one another. With the beam splitter acting as the mirror. So the 45 degree angle one one side is the same on the other side.

 

[circulus vitios]

Yeah, I feel like I don't understand the spacial relationship between the splitter, the viewing screen, the normal of the splitter, the angles, etc. Oh well.

 

[richkaj]

Ok, let's look at the screen. You are facing it. The incoming light isn't facing it straight forward. It is at an angle. The light goes in and is also reflected. The normal gives a 45 degree incidence and reflection...

Look at the incoming beam. It hits the screen and reflects. When a normal line is placed in between with a total internal reflection gives 45 degrees for each one.

 

[Chasing Never Land]

Hi everyone -

I'm still beyond confused. I must be using the wrong normal line, b/c when no matter how I look at it I get that the angle between the normal to the glass and the incident/reflected beam is either 0 or 180. And when I try and look at the normal to the viewing screen, I'm not sure what to use as the incident light ray. But regardless of whether I use the very first incident ray or the refracted ray, I still get angles of 180/0 or 90.

I'm normally good with picturing things, but this is driving me nuts. HELP!!!!!!

(I know this is asking a lot, but if anyone out there labelled the angles, could you upload a pic? )

 

[studyingtoo714]

Sent from my iPhone using SDN mobile

 

[studyingtoo714]

This is my attempt at this question although I still remain unclear about the rays. The math makes sense but not the drawing of the rays.


Sent from my iPhone using SDN mobile

 

[studyingtoo714]

Sent from my iPhone using SDN mobile

 

[alyssa100x]

View attachment 216962

"If you go back to your physics book, it will say that for reflected light, theangle of incidence equals the angle of reflection. The passage says that the reflected light reflects "at a right angle", which is 90 degrees. Thus the angle of incidence (and the angle of reflection) are each 45 degrees, which sum up to the 90. The question asks what the angle of incidence is."

 

[prince_]

Hopefully this clears things up (click on attached file)

 

[themgoals]

Hopefully this clears things up (click on attached file)

Nice!