Refraction Through Prism & Finding Angle of Deviation Experiment for i = 45 | Physics Demo STD 10

Summary

This video tutorial focuses on the practical aspects of using a glass prism in an experiment, addressing common queries and misconceptions. It explains that the angle of incidence is not equal to the angle of emergence in a prism, except in the special case of minimum deviation. The step-by-step demonstration includes setting up the experiment, measuring angles, and determining the angle of deviation. The tutorial emphasizes accuracy and allows for minor human errors, encouraging viewers to comment with any doubts. The video concludes with a thank you message for the support received.

Takeaways

• 🔬 The experiment involves using a glass prism to demonstrate the principles of light refraction and the angles involved, clarifying that the angle of incidence is not equal to the angle of emergence in a prism, unlike a glass slab.
• 📚 The script emphasizes the special case of 'minimum deviation' where the angles of incidence and emergence are equal, which only occurs when the prism is positioned in a specific way.
• 📏 The experiment requires marking and measuring angles accurately, using a protractor to determine the angle of incidence, which is set at 45 degrees in this demonstration.
• 📍 The setup includes an A4 size paper attached to a wooden board, with pins used to align and mark the paths of light rays.
• 📌 The experiment involves aligning pins to create a straight line with the images of the pins seen through the prism, ensuring the accuracy of the light path observation.
• 👀 It's important to view the experiment from the correct angle, with one eye closed and the eye parallel to the surface of the prism to observe the alignment of the pins' images.
• 📝 The script instructs on marking the locations where the pins are aligned with the images, which helps in tracing the path of the light rays.
• 📐 The angle of emergence is measured using a protractor, and it is found to be approximately 53 degrees in this experiment, differing from the angle of incidence.
• 📉 The angle of deviation is calculated by extending the incident and emergent rays and measuring the angle between them, which is approximately 38 degrees.
• 🔍 The refractive index can be determined using Snell's law and the measured angles of incidence and emergence.
• 📊 The experiment concludes with the suggestion to plot a graph of the angle of incidence versus the angle of deviation to find the minimum deviation and understand the relationship between these angles.

Q & A

What is the main purpose of repeating the prism experiment in the video?

The main purpose is to clarify the misconception that the angle of incidence is always equal to the angle of emergence when dealing with a glass prism, and to demonstrate the correct procedure for conducting the experiment.

Why is the angle of incidence not equal to the angle of emergence in a glass prism experiment?

The angle of incidence is not equal to the angle of emergence in a glass prism experiment because it only happens in a special case known as the minimum deviation case. This does not occur with a glass slab where the angles are generally equal.

What special case allows the angle of incidence to be equal to the angle of emergence in a prism?

The special case is known as the minimum deviation case. When the prism is positioned to achieve minimum deviation, the angle of incidence becomes equal to the angle of emergence.

How is the angle of incidence set in the experiment described in the script?

The angle of incidence is set by using a protractor to mark a 45-degree angle on the A4 size paper where the prism is placed.

What is the significance of marking the center of the A4 size paper with a dot?

Marking the center of the A4 size paper with a dot helps to accurately place the prism and ensures that the experiment is conducted symmetrically around the center point.

Why are two pins used in the experiment, and what is their purpose?

Two pins are used to create a reference for the angle of deviation. They are placed at a distance and their images are aligned to form a straight line, which helps in determining the path of the refracted and emergent rays.

What is the approximate distance between the two pins used in the experiment?

The approximate distance between the two pins is about 7 centimeters, as mentioned in the script.

How is the angle of emergence measured in the experiment?

The angle of emergence is measured by aligning a protractor with the emergent ray and the normal to the prism surface, then reading the angle formed.

What is the method to find the angle of deviation in the experiment?

The angle of deviation is found by extending the emergent and incident rays with dotted lines and measuring the angle formed between the extended lines using a protractor.

How can the refractive index be determined using the angles of incidence and emergence?

The refractive index can be determined using Snell's law, which relates the angle of incidence and the angle of refraction. By measuring these angles, one can calculate the refractive index of the prism material.

What is the significance of plotting a graph of the angle of incidence versus the angle of deviation?

Plotting a graph of the angle of incidence versus the angle of deviation helps to visualize the relationship between these angles and to identify the minimum deviation point, which is important for understanding the optical properties of the prism.

Outlines

00:00

🔬 Prism Experiment Revisited

The speaker reiterates the importance of understanding the behavior of light through a glass prism, clarifying misconceptions about the equality of angles of incidence and emergence. They emphasize that this only holds true in the special case of minimum deviation. The practical demonstration involves setting up an experiment with a protractor and pins on an A4 paper to measure the angle of incidence at 45 degrees. The goal is to align the images of the pins with the prism to appear in a straight line, illustrating the path of light through the prism.

05:02

📏 Measuring Angles in the Prism Experiment

After setting up the experiment, the speaker proceeds to measure the angle of emergence and deviation using a protractor. They carefully mark the locations where the pins were placed, join these points to the prism surface, and measure the angles formed. The speaker explains the process of finding the angle of deviation by extending the rays and measuring the angle formed between the extended emergent and incident rays. They also mention the possibility of slight human error in the experiment and how it can affect the results.

10:06

📈 Analyzing and Plotting Prism Experiment Data

The speaker concludes the experiment by discussing the analysis of the measured angles and the importance of plotting a graph of angle of incidence versus angle of deviation. They mention the concept of minimum deviation and how the angle of incidence equals the angle of immersion at this point. The speaker encourages viewers to perform the experiment with different angles of incidence to understand the relationship between the angles more clearly. They also address common concerns about the equality of certain angles in the experiment and emphasize the acceptability of minor discrepancies.

Keywords

💡Prism

A prism is a polyhedron with two congruent and parallel faces called bases, and all other sides are parallelograms. In the context of the video, a glass prism is used to demonstrate the principles of light refraction and dispersion. The script explains that unlike a glass slab, the angle of incidence and emergence are not equal in a prism except in the special case of minimum deviation.

💡Angle of Incidence

The angle of incidence is the angle at which a ray of light strikes a surface. In the video, the presenter sets the angle of incidence to 45 degrees to demonstrate the refraction through a prism. The script emphasizes that this angle is not equal to the angle of emergence in a prism, contrary to what happens with a glass slab.

💡Angle of Emergence

The angle of emergence is the angle at which light exits a medium after refraction. The video script describes measuring this angle using a protractor after the light has passed through the prism, finding it to be approximately 53 degrees, which is different from the angle of incidence.

💡Minimum Deviation

Minimum deviation is a special condition in optics where the angle of incidence equals the angle of emergence when light passes through a prism. The video script clarifies that this only occurs under specific conditions and is not the general rule for all prisms.

💡Refraction

Refraction is the change in direction of light as it passes from one medium to another due to a change in speed. The video demonstrates refraction by showing how light bends when it enters and exits the prism.

💡Snell's Law

Snell's Law, also known as the law of refraction, relates the angles of incidence and refraction to the indices of refraction of the two media. The script mentions using Snell's Law to verify the angle of refraction when the angle of incidence is known.

💡Refractive Index

The refractive index is a measure of how much light slows down and bends as it passes through a medium. The video script suggests that one can calculate the refractive index using the measured angles of incidence, emergence, and deviation.

💡Angle of Deviation

The angle of deviation is the angle between the incident ray and the emergent ray after refraction. In the script, the presenter measures this angle to be approximately 38 degrees and explains how it is related to the angle of incidence and the properties of the prism.

💡Equilateral Triangle

An equilateral triangle is a triangle with all three sides of equal length and all three angles equal to 60 degrees. The video script refers to the shape of the prism, which is an equilateral triangle, to explain the relationship between the angles of incidence, emergence, and deviation.

💡Practical Experiment

A practical experiment is a hands-on activity that demonstrates scientific principles. The video script describes a step-by-step process of conducting an experiment with a prism to observe and measure the effects of light refraction and deviation.

💡Graph Plotting

Graph plotting is a method used to visualize data by plotting values on a graph. The script mentions that after obtaining various angles of incidence and deviation, one should plot a graph to find the minimum deviation and the corresponding angle of incidence.

Highlights

The angle of incidence is not equal to the angle of emergence in a glass prism, unlike in a glass slab.

Angle of incidence equals angle of emergence only in the special case of minimum deviation in a prism.

In the experiment, a glass prism is placed on an A4 size paper, and a protractor is used to measure angles.

The angle of incidence is set to 45 degrees, and pins are used to trace the light path.

Two pins are placed at a distance of at least 5 centimeters from each other to determine the path of the incident ray.

The emergent ray is traced by aligning two additional pins with the images of the first two pins as seen through the prism.

The angle of emergence is measured using a protractor and found to be roughly 53 degrees.

The angle of deviation is determined by extending the emergent ray backward and the incident ray forward.

The angle of deviation is measured to be approximately 38 degrees.

The angle of refraction is found to be around 33 degrees using the refracted ray.

The sum of the angle of incidence and the angle of emergence should be equal to the sum of the angle of the prism and the angle of deviation, allowing for minor human error.

For a 60-degree prism, the calculation shows that 45 degrees (incidence) + 53 degrees (emergence) equals 98 degrees, and 60 degrees (prism) + 38 degrees (deviation) also equals 98 degrees.

The experiment allows for an error margin of about one or two degrees.

To obtain the minimum deviation graphically, different angles of incidence are tested, and a graph is plotted with the angle of incidence on one axis and the angle of deviation on the other.

The point of minimum deviation on the graph indicates where the angle of incidence equals the angle of emergence.

Transcripts

and I am going to repeat the Bold

practical of prism once again

there are many queries in that

particular experiment so I have decided

to make video once again please note

that

this is a glass prism that we are going

to use and unlike the glass slab

angle of incidence will not be equal to

the angle of emergence it happens only

in the glass slab many many people have

commented that I should be equal to e

But please understand that angle of

incidence is equal to angle of emergence

in all cases in case of glass lab not in

case of prism it happens only in a

special case which is known as minimum

deviation case so when the prism is in

minimum deviation at that time only the

angle of incidence and emergence are

equal so practically we don't know which

angle

V for the angle of incidence we will get

the minimum deviation right

so please do not expect that angle of

incidence will be equal to angle of

emergence in case of the class prism

right

so now let's quickly proceed further and

I'm going to make the angle of incidence

45 degree this time and I am going to

repeat the practical

so as you can see that I have uh

clamped two soft board pins on an A4

size paper these are some basic

stationeries and this A4 size paper is

well attached on this wooden board

so now we are going to take the prism

and we are going to place it exactly at

the center of the A4 size paper we are

going to press it with our thumb and we

are going to out mark it

[Music]

like this

okay

now exactly at the center I am going to

make a DOT

then I am going to place the protractor

and

one dot I am going to make it at 90

degree

another at 45 degree

this line

is the normal

which is perpendicular to the surface

now this is going to be my incident rate

this is 90 degree this is 45 degree so

the angle of incidence is 45 degree

now

we are going to place

two pins

which are at least at a distance of

5 Centimeters from each other

please note that when you fix the pins

you will find it

the pins to be not piercing at some

locations

so you try different areas do not take

up the prism and try to bang it right

that looks very very odd so now

approximately I would think that the

distance is more than yes it is more

than 5 Centimeters this is roughly

six point six centimeters no it's all

approximately seven centimeters okay so

we are good to go now I am going to

place the prism back at the traced

location and then I'm going to see the

images of these two pins from this side

and then I am going to place another two

pins

here such that one here and the another

here such that these two pins and the

images of these two pins appear in a

perfect straight line

you need to get down from where you are

sitting

and you need to close one of your eyes

your eyes must be parallel

to the surface of the bone

as you can check by yourself that the

images of those two blue pins they are

appearing from this side of the prism

[Music]

[Music]

foreign

[Music]

pins they are appearing in the perfect

straight line This step has to go very

very well for the accuracy of the

experiment

now I am going to remove the pins

and mark the pricked locations

I am going to place the prism back at a

safe place remove these two pins and now

I am going to join these two points with

this prism surface let me name the prism

surface is as ABC then I am going to

join these two points P1 and P2 which

are the brick locations with the surface

AC of the prism

this is going to be my emergent Ray

now I am going to join these two points

this is say Point P3 and this is point

P4

this is going to be my refracted Ray

refracted Ray this is incident Ray

this is refracted Ray this one is the

emergent Ray now very carefully I am

going to place the protractor back

at surface AAC

and this point should be matching with

this point

like this

line of the protractor should match with

surface AC

now pointing at

90 degree

this is my normal

I'm going to join these two points let

the normal be long enough

[Music]

so this is my angle of emergence e and I

am going to measure the angle of

emergence by using the protractor please

put the protractor like this such that

this line should match with our emergent

Ray

like this one and this point of the

protractor must match with the

this particular point so I'm getting the

angle of emergence

as

this is 10 20 30 40 50 roughly around 53

degrees so this is the angle of

emergence which is 53 degrees now how

would we find out the angle of deviation

you need to extend this emergent Ray

backwards with a dotted line

like this

and extend the incident Ray forward

like this then the angle which is formed

this angle is the angle of deviation so

we are going to put the protractor back

at its place like this

and then we are going to measure the

angle of deviation

yeah

so from here to here this is 10 degree

20 degree 30 degree and this is

somewhere around 38 degrees so the angle

of deviation is roughly 38 degrees and

please understand that I and E are not

equal now I am just going to write down

all the angles over here this would be

our angle of refraction let us measure

that too

[Music]

for that I will have to extend this

refracted Ray forward

like this one and

then

10 20 30 roughly around 33 degrees is

the angle of refraction

you can also verify with the help of the

Snell's law so angle of

incidence is 45 degree you can also find

out the refractive index using these two

values

the angle of emergence and deviation are

as follows

sorry this is 38 degree and this is 53

degrees

now

I plus e

should be equal to a plus Delta but

since we are doing the experiment there

can be a human error of about one or two

degrees that's perfectly fine you need

not to exactly make them equal okay so I

is 45 degree plus e so that is 45 plus

53 this answer turns to be around

98 Degrees whereas a plus Delta a plus

Delta is equal to the angle of prism is

60 degrees because it is an equilateral

triangle

so 60 degrees plus 38 degrees so this is

perfectly 98 Degrees I was not expecting

this one but if you really do it with a

great trigger you may get the correct

answer if these two are not equal that's

perfectly fine many people have

commented a lot about this that these

two angles are not equal but that's

perfectly fine

two degrees error here and there is

allowed in the experiment you need not

to worry about that so now

all the angles are given and similarly

you can make the angle of incidence as

60 degrees 30 degrees other angles and

then you can find out the other angles

as well finally you will need to plot a

graph of

I

and Delta so here the angle of deviation

and then here the angle of incidence and

then for all the other values you will

have to plot the graph for angle of

incidence and for the angle of deviation

you will get similar kind of graph

this is the point which is the minimum

deviation Delta minimum and over here at

that angle the angle of incidence will

be equal to the angle of immersion so

you have to obtain that part graphically

so I hope this practical is now very

much clear to you still if you have any

doubts please do comment in the comment

section and I am really really very very

thankful to all of you that your support

has made my channel a very very big

success so once again pranam and

namaskar to everybody thank you very

much thanks a lot