EXPERIMENTS IN PHYSICS AND CHEMISTRY

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EXPERIMENT 1: 

AIM:

DEMONSTRATING CONVERGENT RAYS AND DIVERGENT RAYS




Materials required: Rubber foam piece, slipper sole, Pins

Procedure: To understand convergent rays and divergent rays from mirror, we need to take a small piece of rubber foam and draw a straight line. Put the pins along the line drawn, and appears as straight lines coming out from the foam, now bend the piece of rubber foam inwards, and then we can observe that the pins meet at a point, and now bend the rubber foam, outwards then the pins appear that they are moving away from each other.



Conclusions:  Convergent rays meet to a point and divergent rays move away from each other.  The experiment also help us to understand the concept of normals to the curved surfaces, in the first case, the pins act as normals to the concave mirror and in the second case, the pins move away from a point.  The distance between converged or diverged point to surface is called Radius of curvature and the line is called normal.   

EXPERIMENT 2:

AIM: To find the focal length of a given concave mirror.

Materials required : Concave mirror, Screen, V-Stand (holder),                                          meter scale

Procedure: Collect the required materials from your laboratory, take V-stand and place the concave mirror in V-Stand, and to find the focal length of the concave mirror, we can use sun or tree or a person at a distance can be chosen as an object.  If you suppose sun as the object, then face the reflecting surface towards sun, and observe the clear image of the sun as a smallest bright spot on the screen or white paper, if you suppose tree as an object, then face the reflecting surface of the mirror towards the tree and observe an inverted image of the tree on the screen or a white paper.  

                 The distance from the image to the pole of the mirror is known as focal length of the mirror.  This distance is the distance between image and mirror as observed practically.

                We can observe the variation in size of the image when we move the screen towards or away from the Focus.

Precautions: Measure the distance accurately, look at the size of the screen or white paper which should not obstruct incoming sun rays.

EXPERIMENT 3:

AIM: To find the focal length of the given convex lens

Materials required: Convex lens, V-stand, screen, candle,                                              meter scale

Procedure: 

                       Collect apparatus or materials required from laboratory, place the convex lens in v-stand, and place the screen on one side of the lens, and allow the light rays coming from distant object such as a tree.  Adjust the distance from the screen to the lens such that the image of the tree should be clear.  The distance from the image to the optic center of the lens is called the focal length of the lens.  

Precautions: screen, lens should be on the same line.

Result:

Focal length can be also called as minimum limiting object distance. 

EXPERIMENT 4:

AIM: To understand the change in focal length of lens with surrounding medium

Materials required: Convex lens, Circular lens holder, glass tumbler, Black stone

Procedure: 

Before doing the experiment, find out the focal length of the given convex lens using distant object method, and note down the value.  Use the same lens and place in a lens holder.  Place a black stone at the bottom in glass tumbler which is filled with water.  Now slowly, place the lens holder with lens into the water, to see the clear image of the black stone.  The distance from the black stone to the lens will become the focal length of the lens.  

Precautions: Place the lens holder slowly into the water, the length of the tumbler should be at least 5 times than that of the focal length of the lens.  

Result & Observations:

We observe that the focal length of the convex lens is increased when it is placed in water.  We understand that the focal length depends on surrounding medium of the lens also.

  

EXPERIMENT 5

AIM: To calculate/find the Least distance of distinct vision of eye

Materials required: 30 cm scale, Any printed material(news paper, textbook), observer

Procedure:

To identify the least distance of distinct vision of eye, read a text book or news paper, at certain distance from your eye.  Now you are able to read the contents from the book or paper, now you try to move the book or paper towards your eye till the contents are unable to read by you.  Then you try to increase the distance from your eyes till you get clear/clarity of the letters.  Ask your friend to measure the distance between your eyes and the book, this distance will be the least distance of the distinct vision of your eyes. Check the distance frequently, you can understand that whether there is any eye defect or not.

Precautions:

Hold the book properly, measure the distances accurately.

Conclusion: 

Least distance of distinct vision can be varied with age.


EXPERIMENT 6



AIM: To understand dispersion of light - splitting of white light ray into seven colours

Materials required: Prism, Source of white light, [a dark room], a screen

Procedure .....The splitting of white light ray into its constituent colours is known as dispersion.  To do this activity, take a prism and white light source and allow the white light to pass through the prism, then we get seven colours called VIBGYOR.

Precautions: To get a narrow beam of light, white light should be allowed to pass through a small hole of paper or wooden plank.


Observations: When white light passes through a prism, dispersion takes place and refraction can be observed.  

The angle of deviation is different for different colours.  Violet is deviated maximum and red is deviated least. 




EXPERIMENT 7:

AIM: To prove white light is constituent of seven colors.

MATERIALS REQUIRED: Plane mirror, sunlight from sun, small tub with water

PROCEDURE:

Take small tub and fill it with water, place the plane mirror in water such that it makes some angle with water surface and make it in the presence of sunlight, the water droplets act as prism and makes the white light into seven colors and these are reflected from the mirror and arrange the reflected light to fall on to the white wall.  One can observe the formation of rainbow.  

precautions to be taken:

1. arrange the demonstration under the presence of sun light.

2. the mirror should be at certain angle to the surface of water

Observations:

-white light is constituent of seven colors (VIBGYOR).

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Balancing a Chemical Equation

How to balance a chemical equation?

A chemical equation tells us the type of reaction between different reactants. Chemical equation gives the states of the reactants and products.  One can calculate the amount of products required for required amount of products.

To balance a chemical equation, very interesting method is algebraic expression method.


for example:  C3H8 + O2 -----> CO2  + H2O



The above reaction is to be balanced using algebraic expressions

step 1) the coefficients of Each reactants and products assumed to be a,b,c,d,...

                    aC3H8 + b O2 -----> c CO2  + d H2O

step 2) identify and count the number of elements on both sides of the reaction

                    carbon: 3a = c

                    hydrogen: 8a = 2d

                    oxygen:  2b = 2c + d

                    

step 3) let us assume a=1, then simplify the equations for other variable values

                        c = 3,     2d = 8   then d = 4             if d=4 and c =3 then 2b=6 + 4 = 10, b=5

step 4) write the chemical equation using the variable values

            C3H8 + 5O2 ---> 3CO2  + 4 H2O



step 5) count the number of atoms on both sides

                   carbon atoms  = 3
                  hydrogen atoms = 8
                  oxygen atoms = 10 




step 6) we conclude that the equation is said to be balanced. 

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Stephen Hawking ....

Stephen William Hawking....great Mathematician, Physicist

Prof. Stephen william Hawking was born on 8th Jan. 1942, in Oxford, England.  Stephen studied at St. Albans School.  Stephen was awarded Ph.D. titled "properties of Expanding Universe" in 1965.  Stephen William Hawking  was an English theoretical Physicist and Cosmlogist.

Important Concept from Stephen William Hawking.......

1. Hawking radiation:

This is the black body radiation which is supposed to be released by blackholes due to Quantum effects.  This leads to black hole evaporation, the meaning is, Hawking radiation reduces the mass and energy of blackholes.

AWARDS :

1. The Adams Prize: The prize is named after the mathematician "John Conch Adams"

2. Eddington Medal: Royal Astronomical society awards the Eddington Medal.  

3. Fundamental Physics Prize: It is awarded by Fundamental Physics Prize Foundation

TOP BOOKS WRITTEN BY STEPHEN WILLIAM HAWKING:

"A Briefer history of time" a famous book written by Stephen Hawking.  A Briefer history of time books gives explanation on all the forces of physics.  

Another book - "The Universe in a Nutshell". 

Stephen is a fellow of the Royal society and he is a member of the US National academy of Science.

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LENS & LENS MAKER'S FORMULA

What is a Lens?

A transparent medium bounded by two surfaces, at least one of the surface should be a curved, is said to be a lens and it is said to be THIN LENS, When there is a small gap between the two surfaces or lenses where the thickness are much less and considered negligible in comparison to the radius of curvature.

LENS MAKER'S FORMULA:

When a lens of refractive index n2 is placed in the medium of refractive index n1, and the radii of curvatures of lens are R1 and R2, then we can write

                     ( n1/v)-(n1/u)  =  (n2-n1)[1/R1  -  1/R2]

dividing the equation by n1,

           we get,   1/v  -  1/u  =  (n2/n1  - 1)[1/R1 - 1/R2]

when the object is at infinity, u = infinity,  and then the image distance v = f, then

lens maker's formula is    1/f = (n2/n1  - 1)[1/R1 - 1/R2]

                                       1/f =(n-1)[1/R1 - 1/R2]



LIMITATIONS OF LENS MAKER'S FORMULA :

- the lens should be thin to consider above formula and the medium is same on either side of the lens.


sign conventions:

for convex lens:

R1 is positive,  R2 is negative and f is positive

for concave lens:

R1 is negative, R2 is positive and f is negative

PROBLEMS USING LENS FORMULA:

1. An object is placed at 8 cm from a lens of  focal length 15 cm, then calculate the image distance and determine whether the image is real or virtual.


2. A student using a lens of focal length -15cm, and object is placed at 20 cm from it, then calculate how far the image is from the lens and find out the magnification.  Conclude whether the image is real or virtual.

3. Calculate the image distance and determine whether the image is real or virtual when an object is placed at 20 cm, from a lens of negative focal length -10cm.

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What is net neutrality?

NET NEUTRALITY.........

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Refraction of light at curved surfaces - do you know?

Refraction of light at curved surfaces.....do you know?

How do you differentiate lens and spherical mirror?

Differentiate focal length and Focus?

Whether pole and optic centre denote same or different?

Differentiate centre of curvature and Radius of curvature?

Can you Identify different types of lenses?

Differentiate beam and ray

Factors effecting focal length of lens

Draw converging beam and diverging beam

What do you term the effective width of a lens through which refraction takes place?

Write lens formula and mirror formula

When do you say an image is magnified or enlarged?

Can you draw ray diagrams for convex and concave lenses?

Can you say convex lens acts both diverging and converging lens...explain 

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REFLECTION AT CURVED SURFACES - PROBLEMS

PROBLEMS IN PHYSICS - REFLECTION AT CURVED SURFACES

PROBLEM 1: 



Where is the image formed when 8 cm tall object is placed at 20 cm. in front of a concave mirror with focal length 5 cm.  Find out the size of the image also.




PROBLEM 2:



A 10 cm tall object is placed in front of a convex mirror of focal length 15 cm, Find out the image distance and write its characteristics .



PROBLEM 3:


10 cm focal length concave mirror is placed at 40 cm, from a wall.  Calculate the object distance such that its image is formed on the wall.



PROBLEM 4:



In front of 15 cm focal length concave mirror, an object is placed at 30 cm, if the object is displaced through 10 cm towards mirror, calculate by how much distance the image is displaced?



PROBLEM 5:



The image is formed behind the mirror, at a distance of 10 cm, when an object is placed at 20 cm in front of it.  Identify the type of mirror used and also calculate the focal length.  

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REFLECTIOIN AT SPHERICAL SURFACES - do you know

DO YOU KNOW? 

 1. Angle of incidence, angle of reflection

 2. Plane mirror, spherical mirrors

3. Normal drawn to plane mirror and spherical mirror

4. Radius of curvature and focal length

5. Relation between R and f

 6. Parallel beam of light

7. Principal axis acts as Normal, discuss

 8. Virtual image and Real image - properties

 9. Situation to get hi=ho in a concave mirror

 10. Characteristics of image formed by convex mirror

 11. Mirror formula - applying to concave and convex mirrors

12. Simplify uv=uf+vf

13. Sign conventions - discussion

 14. The relation between size of image and size of object --> magnification

 15. The relation between object distance and image distance --> magnification

 16. The image formed by convex mirror - explanation

17. Uses of concave and convex mirrors

 18. Working principle of solar cooker

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BENEFITS OF TULSI LEAVES

IMPORTANCE OF TULSI LEAVES....

Tulsi is very important and most prominent herbs in the society.  We use to call the tulsi as 'king of herbs'.  The scientific name of the tulsi is 'ocimum tenuiflorum'.  Tulsi has been cultivated for more than 6000 years.  It is mostly used in Southeast asian countries. Tulsi plant can protect us from many infections.  Let us look at the health benefits of tulsi...

1. ORAL HEALTH:

Tulsi acts as very good mouthwash which can control oral plaque since it has very high antibacterial activity.

2. USEFUL TO PREVENT EYE DISORDERS:

Tulsi leaves protect the eye from free radiacals and environmental damage.

3. VERY GOOD FOR PROTECTING BLOOD VESSELS

Tulsi leaves possess antiinflmmatory and antioxidant properties, it can remove plaque in blood vessels.

4. TULSI CAN INCREASE IMMUNITY

Respiratory disorders like asthma can be treated using tulsi.

5. LIVER CAN BE PROTECTED

6. BLOOD SUGAR LEVELS CAN BE REGULATED


Tulsi can support blood sugar regulation by increasing insulin secretions in type2 diabetes people.

7. PREVENTS KIDNEY STONES

Tulsi helps to reduce uric acid level in the body, it has the property to to clean out the kidneys.

8. SKIN CARE

By consuming tulsi, one can be free skin from all infectios.

9. TULSI PREVENTS PREMATURE AGING

The free radical damage can be reduced by tulsi.

10. EFFECTIVE TO CURE COUGH AND COLD.

Tulsi is considered a sacred plant and it is also used as antiinflammatory and stress reducer.

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Raman Effect - National science day

About Chandrasekhara Venkata Raman (1888-1970)

C.V. Raman was born on Nov.7, 1888 in Trichiopoly (Tiruchirapalli). The Raman's family lived on a low income when Raman was born.  C.V. Raman was awarded both Bachelor and Master's degree before Raman turned 20.

Why National Science Day is celebrated on Feb.28th?

In India, National science day was celebrated first on Feb.28, 1987.  Then onwards we are celebrating National Science Day on Feb.28, this is to mark the discovery on the "Raman Effect" by Indian Physicist, sir C.V. Raman on 28 Feb. 1928.

What is Raman Effect?

While C.V. Raman travelling to Europe in the early 1920s, he noticed that the sea water is in blue color.  This leads to the discovery of the Raman Effect.


Definitions:

I. Change in the wavelength of light that occurs when a light beam is deflected by molecules.

II. Certain molecules cause waves radiation to scatter differently than the other molecules.

III. Raman effect is an inelastic scattering of photon.  Change in the wavelength of light that occurs when a light beam is deflected by molecules.  During  scattering, a very few photons undergo a change in behaviour.

Experiment: When there is an interaction between the particles of  the liquid and the photons to be responsible for the change in the behaviour of the photons.

Why National science day is celebrated on Feb.28?

In India, the first National science day was celebrated on Feb. 28, 1987, then onwards continuously celebrating National science day.  The reason behind it is that to mark the discovery of the "Raman Effect" by Indian physicist sir C.V. Raman on 28 Feb. 1928.

Applications of Raman Effect:


I. NON-DESTRUCTIVE TESTING:  Scientists using the raman effect for analysing the atomic structures of the particles without causing any destruction to the substance.

II. Raman effect - Raman spectroscopy is being used to study the properties of different materials.

III. The chemical constitution of the substances also can be analysed by Raman effect.

DAILY LIFE EXAMPLES:

Why the sky is blue?

As we all know that when light travels in a straight light, and something gets in its path - that may reflect the light, bend it, or scatter it.  By using these known properties we can explain it.

When sunlight passes through the atmosphere, due to the gases & particles present in air, the light is scattered in all the directions.  Sunlight is combination of seven colors, among them, blue is scattered more than the other colors because it travels as shorter and smaller waves.  Blue color is reached to our eyes from all the directions, that is most of the time we see a blue sky. 

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