Plus Two Physics

Van de Graff Generator Pics

Common Engineering Entrance Test Not Welcomed By IITs

The Indian Institutes of Technology have rejected the idea of selecting the candidates through a Common Engineering Entrance Test for all engineering colleges. HRD ministry-appointed committee said in its report, “Scores in a well-designed National Aptitude Test should be used to capture parameters of interest such as raw intelligence, aptitude, general awareness, comprehension and written communication skills. NAT should not require extensive preparation and coaching. The questions should be designed in such a way that it would not require inputs beyond plus 2 level.” To make the exam process more friendly for students, the committee has proposed to make NAT an online test conducted throughout the year.

MODEL QUESTION PAPER FOR AISSCE 2008

PHYSICS

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.

_____________________________________________________________________________________

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.
8. 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.

   

9. 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.
10. 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.
11. Show that the total energy stored in an inductor L, when a current I is established through it is ½ LI² .
12. 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.
13. 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.

    

14. 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.
15. Find the wavelength of electromagnetc waves of 5 x 10¹⁹ Hz in free space. Give its two applications.
16. 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, how does the angular width of the central maximum vary when

    1. Aperture of slit is increased
    2. Distance between the slit and screen is decreased. Justify your answer in each case.
17. A galvanometer coil has a resistance of 12 ohm and the meter shows full scale deflection for a current of 3 mA. How can you convert the galvanometer into a voltmeter of range 0 to 18 V
18. V-I graphs for parallel and series combination of two metallic resistors are shown in figure. Which graph represents series combination? Justify your answer.

    

19. Apply Gauss’ theorem to obtain an expression for electric field due to an infinite plain sheet of charge.
20. In figures (a), (b) and (c) are shown three ac circuits with equal currents. If the frequency of the emf is increased, then what will be the effects on the current flowing through them? Explain with reason.

    

21. A convex lens made of a material of refractive index n₁ is kept in a medium of refractive index n₂. Parallel rays of light are incident on the lens. Complete the path of the light rays emerging from the convex lens if,

(i) n₁>n₂     (ii) n₁=n₂     (iii) n₁<n₂

1. Derive an expression for the angular width of central maximum of diffraction pattern produced by a single slit illuminated with monochromatic light.
2. Radiation of frequency 10¹⁵Hz are incident on two photosensitive surfaces A and B. Following observation are recorded.

   Surface A: no photoemission takes place

   Surface B: Photoemission takes place but photoelectron has zero energy

   Explain t
   he above observation on the basis of Einstein’s photoelectric equation. How will the observation with surface B changes when the wavelength of incident radiation is decreased?

3. The sequence of stepwise decays of radioactive nucleus is

   
   

   If the mass number and atomic number of D₂ are respectively 176 and 71, what are the corresponding values for D and D₄ nuclei. Justify your answer.

4. Explain with the help of a neat diagram, the action of transistor as a switch.

   OR

Explain through a labeled circuit diagram the use of a transistor as an oscillator.

1. What is amplitude modulation? Represent the process graphically. Write two limitations.
2. What is an intrinsic semiconductor? How can these materials be converted into (i) P-type (ii) n-type extrinsic semiconductor. Explain with the help of energy band diagram.
3. Find the magnetic field induction at a point on the axis of a circular coil carrying current and hence find the magnetic field at the centre.

   OR

   1. Explain briefly the magnetic elements of earth.
   2. At a certain location in Africa, a compass points 12° west of the geographic north. The north tip of the magnetic needle of a dip circle placed in the plane of magnetic meridian points 60° above the horizontal. The horizontal component of earth’s magnetic field is measured to be 16 gauss, specify the magnitude of earth’s field at the location.
4. (a) State the principle of a potentiometer with the help of circuit diagram. Describe a method to find the internal resistance of a primary cell.

   (b) Two primary cells of emf E₁ and E₂ (E₁>E₂) are connected to the potentiometer wire AB as shown in figure.

   If the balancing lengths of the two combinations of cells are 250 m and 400 m. find the ratio of E₁ and E₂

   OR

   What is drift velocity? Establish the relation between drift velocity and electric current. Deduce ohm’s law using the concept of drift velocity.

5. With the help of a ray diagram, show the formation of mage of a point object by refraction of light at the convex spherical refracting surface separating two media of refractive indices n₁ and n₂ (n₂>n₁) respectively. Using this diagram derive the relation

Write the conventions used.

OR

Deduce lens maker’s formula for a thin biconvex lens. How does the focal length of a convex lens change if monochromatic red light is used instead of monochromatic blue light?

ELECTROSTATICS TEST PAPER FOR CLASS XII

1. What orientation of an electric dipole in a uniform electric field corresponds to its stable equilibrium?

2. What is the area of the plates of a parallel plate capacitor of capacitance 2F and with separation between plates 0.5 cm?

3. What is the work done in carrying a point charge 10 nC between two points separated by a distance 5 cm on an equipotential surface?

4. A parallel plate capacitor is made by stacking ‘n’ equally spaced plates connected alternatively. If the capacitance between any two plates is ‘C’, determine the resultant capacitance of the combination

5. Calculate the coulomb force between two a particles separated by a distance of 3.2 x 10^-15 m

6. Draw graph showing variation of electric field with distance for a uniformly charged metallic sphere.

7. An electron and proton are free to move in an electric field. Which one will have greater acceleration? Why?

8. Sketch two equipotential surfaces for (a) a point charge. (b) between two plane sheets of charge.

9. Show that the work done in rotating an electric dipole of dipole moment p in a uniform electric field E by an angle θ from the equilibrium postition W = PE(1-cos θ)

10. The given graph shows the variation of charge ‘q’ verses potential difference for two capacitors C1 and C2 .The capacitors have same plate separation, but the plate area of C2 is double that of C1.Identify the line in the graph corresponding to C1 & C2 and why?

11. Derive an expression for the torque acting on an electric dipole placed in a uniform electric field.

12. Derive an expression for the capacitance of a parallel plate capacitor.

13. You are given three capacitors of value 2μF, 3μF, 6μF. How will you connect them to a resultant capacity of 4μF?

14. Two equally charged identical metal spheres A and B repel each other with a force of 2·0 x 10^-5 N. Another identical uncharged sphere C is touched to A and then placed at the mid point between A and B. What is the net force on C?

15. A dielectric slab of thickness t introduced between the plates of a parallel plate capacitor separated by a distance d. (t < d). Derive an expression for the capacitance of the capacitor

16. Describe the principle construction and working of a Van de graff Generator with the help of a neat labeled diagram.

17. Use Gauss theorem to derive an expression for the electric field at a point due to

a. an infinite plane sheet of charge of uniform charge density σ

b. a thin infinitely long straight line  of charge of uniform charge density λ

************************

What is a Parallelopiped (Also named Parallelepiped)

A parallelopiped or parallelepiped is a three-dimensional figure formed by six parallelograms. (See figure)

Scope and Excitement of Physics

I have decided to write this short article because Many students asked me to give them an easy way to Write a note on the Scope and Excitement of Physics

Scope of Physics

Scope relates to the field of study in Physics. That is what all things are included in the study of Physics.

When discussing Physics, it would be better to ask what not is included. Physics discusses anything in the universe. Physics is the study of matter and energy with which the entire universe is made up of.

To Quote from the NCERT Text

“The scope of physics is truly vast. It covers a tremendous range of magnitude of physical quantities like length, mass, time, energy, etc. At one end, it studies phenomena at the very small scale of length (10^-14 m or even less) involving electrons, protons, etc.; at the other end, it deals with astronomical phenomena at the scale of galaxies or even the entire universe whose extent is of the order of 10²⁶ m. The two length scales differ by a factor of 10⁴⁰ or even more. The range of time scales canbe obtained by dividing the length scales by the speed of light : 10^–22 s to 10¹⁸ s. The range of masses goes from, say, 10^–30 kg (mass of an electron) to 10⁵⁵ kg (mass of known observable universe). Terrestrial phenomena lie somewhere in the middle of this range.”

In Physics, we study from extremely small  to  extremely large. Physics discusses the beginning of the universe and the various phenomena occuring recurrently in the universe. Wherever there is matter and energy, there is Physics.

Excitement of Physics

The NCERT Book says,

“Physics is exciting in many ways. To some people the excitement comes from the elegance and universality of its basic theories, from the fact that a few basic concepts and laws can explain phenomena covering a large range of magnitude
of physical quantities. To some others, the challenge in carrying out imaginative new experiments to unlock the secrets of nature, to verify or refute theories, is thrilling. Applied physics is equally demanding. Application and exploitation of physical laws to make useful devices is the most interesting and exciting part and requires great ingenuity and persistence of effort.”

Physics is exciting because

• It trains us in problem solving
• It helps us to have an analytical outlook
• To observe rather than see things
• Everything is explained on the basis of the cause effect relationship, which helps us think logically and decide rationally
• Whether or not, a students of plus two continue to learn Physics, the basic problem solving skill he has acquired during the PlusTwo Physics course will remain with him and will be constantly helping him in all walks of life.