Tuesday, July 26, 2011

CBSE XII (AISSCE) 2006 Physics Question Paper


Outside Delhi

  1. Define the term electric dipole moment. Is it a scalar or a vector quantity.

  2. The variation of potential difference V with length l in case of two potentiometers P and Q ia as shown. Which one of these two will you prefer for comparing the e.m.f.s of two primary cells?

  3. de Broglie wavelength associated with an electron accelerated through a potential difference V is λ. What will be its wavelength when the accelerating potential is increased to 4 V?

  4. Give any one difference between FAX and e-mail systems of communication.

  5. Steel is preferred for making permanent magnets whereas soft iron is preferred for making electromagnets. Give one reason.

  6. You are given 'n' resisitors, each of resistance 'r'. These are first connected to get minimum possible resistance. In the second case, these are again connected differently to get maximum possible resistance. Compute the ratio of the minimum to the maximum values of resistance obtained.

  7. Two capacitors of capacitance 6μF and 12μF are connected in series with a battery. The voltage across the 6 μF capacitor is 2 V. Compute the total battery voltage.
    A parallel plate capacitor with air between the plates has a capacitance of 8 pF. The separation between the plates is now reduced by half and the space between them is filled with a medium of dielectric constant 5. Calculate the value of the capacitance of the capacitor in the second case.

  8. Draw a labelled ray diagram to show the image formation in a refracting type astronomcal telescope. Why should the diameter of theobjective of a telescope be large?

  9. Draw a circuit diagram of a metre bridge and write the necessary mathematical relation used to determine the value of an unknownresistance. Why cannot such an arrangement be used for measuring very low resistances?

  10. Which one of the two, an ammeter or a milliammeter, has a higher resistance and Why?

  11. An alternating voltage of frequency f is applied across a series LCR circuit. Let fr be the resonance frequency for the
    circuit. Will the current in the circuit lag, lead or remain in phase with the appiled voltage when (i)f>fr (ii) f<fr?Explain your answer in each case.

  12. A point charge 'q' is placed at O as shown in the figure. Is VP - VQ positive or negative when (i) q>0 (ii) qJustify your answer.

  13. Using Gauss' theorem, show mathematically that for any point outside the shell, the field due to a uniformly charged thin sphericalshell is the same as if the entire charge of the shell is concentrated at the centre. Why do you expect the electric field inside the shellto be zero according to this theorem?

  14. Distinguish between frequency modulation and amplitude modulation. Why is an FM signal less susceptible to noise than an AMsignal?

  15. Write the order of frequency range and one use each of the following electromagnetic radiations:
    (i) Microwaves.
    (ii) Ultra - violet rays.
    (iii) Gamma rays.

  16. Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. Whatinformation can be obtained from the value of the intercept on the potential axis?
    A source of light of frequency greater than the threshold frequency is placed at a distance of 1 m from the cathode of a photo cell. Thestopping potential is found to be V. If the distance of the light source from the cathode is reduced, explain giving reasons, what changewill you observe in the
    (i) photo electric current
    (ii) stopping potential

  17. Define the term half - life period and and decay constant of a radio active substance. Write the SI units. Establish the relationship between the two.

  18. A neutron is absorbed by a 63Li nucleus with the emission of an alpha particle.
    (i)Write the corresponding nuclear reaction.
    (ii) Calculate the energy released, in MeV, in this reaction.
    Given: mass of 63Li = 6.015126 u ; mass of neutron = 1.0086654 u ; mass of alpha particle = 4.0026044 u ; mass of triton = 3.0100000 u ; Take 1 u = 931 MeV /c2

  19. When an inductor L and a resistor R in series are conected across a 12 V, 50 Hz supply, a current differs in phase from the applied voltage by π/3 radian. Calculate the value of R.
    A 0.5 m long metal rod PQ completes the circuit as shown in figure. The area of the circuit is perpendicular to the magnetic field of flux density 0.15 T. If the resistance of the total circuit is 3Ω , calculate the force needed to move the rod in the direction as indicated with a constant speed of 2 m/s.

  20. State Faraday's laws of electrolysis. Express these in mathematical notation. Name any two applications of electrolysis. NOT IN PRESENT SYLLABUS

  21. What are eddy currents? How are these produced? In what sense are eddy currents considered undesirable in a transformer and how are these reduced in such a device?

  22. A beam of light converges to a point P. A lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is

    1. a convex lens on focal length 20 cm

    2. a concave lens of focal length 6 cm?

    Do the required calculations.

  23. Consider an optical communication system operating at λ ~ 800 nm. Suppose, only 1% of the optical source frequency is the available channel band - width for optical communication. How many channels can be accomodated for transmitting

    1. audio signals requiring a bandwidth of 8 kHz?

    2. Video TV signals requiring an approximate band width of 4.5 MHz?

    Support your answer with suitable calculations

  24. Explain (i) forward biasing, (ii) Reverse Biasing of a P-N junction diode. With the help of a circuit diagram, explain the use of this device as a half wave rectifier.

  25. Draw a neat and labelled diagram of a cyclotron. State the underlying principle and explain how a positively charged particle gets accelerated in this machine. Show mathematically that the cyclotron frequency does not depend upon the speed of the particle.OR
    State Biot - Savart law for the magnetic field due to a current carrying element. Use this law to obtain a formula for magnetic field at the centre of a circular loop of radius R carrying a steady current I. Sketch the magnetic field lines for a current loop clearly indicating the direction of the field.

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