Snell's law of Refraction

[grisgrisy]

interesting video and very informative

[rainprettybb]

youtube is good for education^^

[MsYouknowthename]

what are the names of the equipments used ??

[MegaMakeupify]

Where did you get the sheet of paper with all the angles?

[QuantumBoffin]

@MegaMakeupify The sheet of paper was hand drawn, but it does the job. There are some commercial versions available (PASCo make one, I believe) but, alternatively, you could just photocopy (and enlarge) a protractor.

[9999rox]

Who is snell

[greendayhall]

@9999rox hes a man who evolved from a snail after discovering that light can penetrate tru his shell

[mexus37]

Foartee phiove degrees.

[marmite5599]

Very interesting, I particularly like the parts where you tell the captivated viewer the degrees. A bit long though, got a bit bored at around 0:03

[go2ec4]

ive tried this but the results are not the same ,when i set the light on an angle of 10 the reflected light' angle was 11

[Sapient1989]

@go2ec4 that is because the refractive index of ur medium is different from the one that is used in the vid.

[FreddieCThatsMe]

pofg;p

#

[griffallstar]

so....was the critical angle 45?or 80?

[mrtictac94]

@griffallstar I swear it's meant to be 42 degrees, but this one only started showing strongly at 70 ?

[griffallstar]

so....was the critical angle 45?

[HKNajjar]

How come total reflection does not occur until something very close to 90 deg?

In another video there seemed to be total reflection. Maybe it's because this is a white beam, that one was red?

[QuantumBoffin]

@HKNajjar this demonstration does not show total internal reflection - I plan to add another one that does at some stage. If you look at the ray you will see it always leaves the block travelling along the normal: total internal reflection occurs when this angle become large (about 43 degrees for glass, depending on the grade of glass).

[junior1984able]

Hello,does the glass block have to be circular shaped for it to work??

[Bushater2000]

@junior1984able No, the light ray simply has to impact the glass block (of any shape) at an angle to have noticeable results.

[junior1984able]

@Bushater2000 thank you, one quetion i had in mind also,where could I buy a light projector like the one you have??

[QuantumBoffin]

Any science educational supplier - which depends upon which country you're in. The projector is called a Ray Box - try doing a search for it.

[QuantumBoffin]

Refraction occurs with any glass block but using a semi-circular block makes it a lot easier to measure the angle of refraction.

[junior1984able]

@junior1984able how much would one ray box cost?

[QuantumBoffin]

@junior1984able It works with any transparent object (regardless of shape or material) - light even refracts when it leaves water, which is why it is difficult to judge how deep a swimming pool is.

[mrrshs]

why do you used a glass slab in form of a protector?

[QuantumBoffin]

It just makes measuring the angles a lot easier.

[cheekymonkey0808]

Really good video! I was just wondering is the angle of refraction always lower than the angle of incidence??

[QuantumBoffin]

When light enters a denser substance, such as glass, it slows down. It's this slowing down that makes the angle of refraction less than the angle of incidence. When the light leaves the block it speeds up again - under these circumstances the opposite is true, although you can't see that in this video.

[cheekymonkey0808]

@QuantumBoffin Thankyou- it makes sense now!

[xenialz]

why didnt the light change direction as it left the block? I've been scrounging my textbook for answers but there weren't any :S.

[QuantumBoffin]

The light leaves the block at 90 degrees to the surface (i.e. along the normal line). When light enters of leaves a block stright on in this way it does not change direction: the light only bends if it hits the edge of the block at an angle.

[MizxBluexEyes]

thank you!

[dimi194]

why do you have to use the semi-circular block-like object?

[QuantumBoffin]

You can do the experiment using any glass or Perspex block. The semi-circular block, however, makes it much easier to read the angle of refraction.

[trungli]

Thanks! By the way, is that a regular laser pen?

[QuantumBoffin]

I just used a 24W 12V bulb, along with a narrow slit in front of it. Not sure a standard laser pen would work that well - the beam is too narrow - you might not get a very good trace.

[trungli]

Thanks for the great demo.

Where can I get the glass block and laser pen? I'd like to show my students as well. Thanks!

[QuantumBoffin]

Most educational science suppliers stock such items. Try doing a search for "Pasco" - they're an american company (but have stockists worldwide) and produce some excellent (but pricey) equipment. They also produce a template (better quality than my hand drawn one) to measure angles with.

[JohnCBriggs]

Nicely done. Thanks for sharing.

[shutuplz23]

nice demonstration!

[reyjr2]

This was an awesome demonstration!! I will reproduce this experiment for my class.

[QuantumBoffin]

I have one of my A level students to thank for this method - he did a project on improving the accuracy of the experiment. The method is straightforward (takes a class about 10 to 15 minutes to do) and the results you get are excellent.

[Dablackninja100]

dude i didnt learn nothin all u did wuz shine a light

[QuantumBoffin]

The aim of a video is to demonstrate an experiment concerning refraction, allowing measurements to be taken: it is intended to be used in a classroom with the assistance of a teacher who could then explain it to you.

If you want to understand refraction there are other videos out there that will explain it to you.