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Sunday, January 1, 2017

Equivalent Lens

In this post, we will learn how to find the equivalent focal length or power of the two thin lenses placed in contact with each other.

By Applying Lens formula in 1st lens,


And by Applying Lens formula in 2nd lens,  


Now adding these two lens equations, we get


If "Feq" is the focal length of the equivalent lens, then


Therefore by eq (3) & (4) we get

Also, we know that the power of a lens is inversely proportional to its focal length. 


Solve this problem based on ray optics:-

If the final image of the tree is formed at infinity after refraction from the given combination of three lenses, then find the focal length (f3) ?

If you reach some unexpected result, then what conclusion can you draw from this result ?

Saturday, December 10, 2016

How do aeroplanes fly?

Flight Of An Aeroplane

The aerofoils are designed such that their upper surface is more curved and their lower  surface is less curved.

By doing this, according to Bernoulli's Principle, there is Low Pressure Zone (LPZ) on the upper side and High Pressure Zone (HPZ) on the lower side.

Also, we know that things move from HPZ TO LPZ.

Therefore there develops a lift in the aerofoils.

And finally Aeroplane flies.

Sunday, December 4, 2016

Special case of Bernoulli's Theorem



From this, we can easily say that-

Where there is Low Velocity, There will be High Pressure 
Where there is High Velocity, There will be Low Pressure.

Wednesday, November 30, 2016

12th Class Physics Test Paper- Atoms And Nuclei


                                      CBSE TEST PAPER-01
                      CLASS - XII PHYSICS (Atoms and Nuclei)

1. Name the series of hydrogen spectrum lying in ultraviolet and visible region? [1]

2. What is Bohr’s quantisation condition for the angular momentum of an electron in the second orbit? [1]

3. Define Bohr’s radius? [1]

4. State the limitations of Bohis atomic model? [2]

5. The half life period of a radioactive substance is 30 days. What is the time for 34th of its original mass to disintegrate? [2]

6. How many α and β-particles are emitted when 232, 90 Th changes to 208 ,82 Pb [2]

7. Binding energies of 16, 8O and 35,17Cl are 127.35 MeV and 289.3 MeV respectively.Which of the two nuclei are more stable? [2]

8. THE total energy of an electron in the first excited state of hydrogen atom is -34.eV

(1) K.E. of the electron in this state.
(2) P.E. of the electron in this state and
(3) Which of the answer would change of the choice. Justify your answer?

9. Prove that the speed of election in the ground sate of hydrogen atom is equal to the speed of electron in the first excited state of hydrogen like Li++ atom. [3]

10. Draw a graph showing variation of potential energy of a pair of nucleon as a function of their separation indicate the region in which the nuclear force is (a) Attractive (b) Repulsive. Also write two characteristics features which distinguish it from the coulomb’s force. [3]

11th Class Physics Test Paper- Gravitation


                                       CBSE TEST PAPER-01
                                CLASS - XI PHYSICS (Gravitation)

1. On which fundamental law of physics is Kepler's second law is based? [1]

2. Which is greater the attraction of the earth for 1 kg of aluminum or aluminum or attraction of 1kg of aluminum for the earth?[1]

3. Distance between two bodies is increased to three times its original value.What is the effect on the gravitational force between them?[1]

4. The distance of the planet Jupiter from the sun is 5.2 times that of the earth. Find the period of the Jupiter’s revolution around the sun?[2]

5. Show that for a two particle system F12 = F21[2]

6. State two essential requisites of geostationary satellite? [2]

7. Show that an artificial satellite circling round the earth in an orbit of radius obeys Kepler’s third low?[2]

8. A 400kg satellite in a circular orbit of radius 2 Re about the earth calculate the kinetic energy potential energy and total energy of the satellite? RE = 6.4x106m, M = 6x1024kg[2]

9. Two uniform solid spheres of radii R and 2R are at rest with their surfaces just touching. Find the force of gravitational attraction between them if density of spheres be P?[3]

10. Find expressions for (1) potential energy (2) kinetic energy (3) total energy for an artificial satellite.



Hence, we can say that the velocity of efflux is equal to velocity acquired by a body when falling through a height equal to the height of the liquid above the orifice. 

Tuesday, November 29, 2016