## CBSE 12th Std Physics Numerical from Optics

A convex lens of crown glass(1.5) has a focal length of 15 cm. The lens is placed in (a) water(1.33) and carbon bisulphide(1,65).determine in each case whether the lens behaves as a conveging or a diverging

## What is refractive index?

Refractive index of a substance is a measure of the relative speed of light through that substance. It tells us by what fraction light is slowed down in the medium. Refractive index = speed of light in vacuum /speed of light in the medium Snell’s law...

## TIME 3 HRS                                    MAX MARKS: 70

GENERAL INSTRUCTIONS:

1. All questions are compulsory.
2. There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry 2 marks each, questions 19 to 27 carry 3 marks each and questions 28 to 30 carry 5 marks each.
3. There is no overall choice. However an internal choice has been provided in one question of two marks, one question of 3 marks and all three questions of five marks. You have to attempt ony one of the choices in such cases.
4. Use of calculators is not permitted.

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1. What is the polarizing angle of a medium of refractive index √3 ?
2. Consider the circuit shown, where APB and AQB are semicircles. What will be the magnetic field at the centre ‘C’ of the circular loop?

3. The closed loop PQRS is moving into uniform magnetic field acting at right angles to the plane of the paper as shown in the figure. State the direction in which the induced current flows in the loop.

4. What is the angle between the directions of electric field at any point on the equatorial line of an electric dipole and the dipole moment?
5. Draw the voltage current characteristics of a zener diode.
6. What is the shortest wavelength present in the Paschen series of spectral lines?
7. Name the constituent radiation of the electromagnetic spectrum which
1. Has the wavelength range between 390 nm and 770 nm
2. Is absorbed from sunlight by ozone layer.
In an experiment on photoelectric effect the following graphs were obtained between the photoelectric current (I) and the anode potential (V). Name the characteristic of the incident radiation that was kept constant in this experiment.

Calculate the potential at the centre of a square of side √ 2 m, which carries at its four corners, charges of +2nC, +1nC, -2nC and -3nC respectively. State the condition under which the phenomenon of resonance occurs in a series LCR circuit. Plot a graph showing the variation of current with frequency of the ac source in an LCR circuit. Show that the total energy stored in an inductor L, when a current I is established through it is ½ LI2 . Draw the energy level diagram showing the ground state and next few excited states for H atom. Mark the transition which corresponds to the emission of the spectral series for Balmer series.The graph shows the variation of voltage(V) across the plates of two capacitors A and B versus increase of charge (Q) stored on them, which of the two capacitors have higher capacitance? Give reason for your answer.

A TV tower has a height of 400m at a given place. Calculate its coverage range if the radius of the earth is 6400 km. Find the wavelength of electromagnetc waves of 5 x 1019 Hz in free space. Give its two applications.How does the resolving power of a compound microscope change on]
1. Decreasing the wavelength of light used
2. Decreasing the diameter of its objective lens

OR

In a single slit diffraction pattern,