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Bhushan Kadam asked a question
Subject: Physics, asked on on 27/2/13

Long Type Questions(3 marks)

  1. Define electric field intensity at a point. Derive an expression for the electric field intensity at a point on the axial line of a short dipole.
  2. Show that the potential on the equatorial line of an electric dipole is zero
  3. What is an electric dipole? Derive an expression for the torque acting on an electric dipole, when held in a uniform electric field. Hence, define the dipole moment.
  4. State Gauss theorem in electrostatics. Using this theorem, derive an expression for the electric field intensity due to an infinite plane sheet of charge of charge density σ
  5. Show mathematically that for any point out side the shell, the field due to a uniformly charged thin spherical shell is the same as if the entire charge of the shell is concentrated at the centre.
  6. Apply gauss theorem to find electric field intensity at a point due to an infinitely long thin, uniformly charged straight wire.
  7. Define the capacitance of a capacitor. Give its S.I unit for a parallel plate capacitor, prove that the total energy stored in a capacitor is ½ cv2and hence derive expression for the energy density of the capacitor.
  8. Derive an expression for the capacitance of a parallel plate capacitor when the space between the plates is partially filled with a dielectric medium of dielectric constant k.
  9. Obtain the equivalent capacitance of the network in figure shown below. For a 300V supply determine the charge and voltage across each capacitor.
  10. Give the principle of working of a Van –De – Graff generator. With the help of a labeled diagram describe its construction and working. How is the leakage of charge minimized from the generator?
  11. Establish a relation between drift velocity of an electron in a conductor of cross section A carrying current I and concentration ‘n’ of free electrons per unit volume of conductor.
  12. Define the term resistivity and write its S.I unit. Derive the expressions for
    1. resistance
    2. the resistivity of a conductor in terms of number density of free electrons and relaxation time.
  13. Draw a circuit diagram for a meter bridge two determine the unknown resistance of a resistor why are the connections between the resistors of a meter bridge made of thick copper strips? Find the shift in the balance point of a meter bridge, when the two resistors in the two gaps are interchanged.
  14. With the help of a circuit diagram explain how the internal resistance of a cell can be determine by using a potentiometer? Write the formula used?
  15. Show graphically the variation of resistivity with temperature for
    1. Metals
    2. alloys
    3. semi conductors
    4. non conductor (carbon)
  16. Why is potentiometer preferred over voltmeter to measure the emf of a cell? The potentiometer wire AB shown in the fig. is 400 cm long. Where should the free end of a galvanometer be connected so that the galvanometer shows zero deflection.
  17. Derive the relation between the focal length of a convex lens in terms of the radii of curvature of the two surfaces and refractive index of its material. A convex lens of focal length 40 cm and a concave lens of focal length 25 cm are kept in contact with each other. What is the value of power of this combination?
  18. State the essential condition for diffraction of light to take place. Use Huygen's principle to explain diffraction of light due to a narrow single slit and the formation of a pattern of fringes obtained on the screen. Sketch the pattern of fringes formed due to diffraction at a single slit showing variation of intensity with angle.
  19. State Huygens’ principle. Using the geometrical construction of secondary wavelets, explain the refraction of a plane wave front incident at a plane surface. Hence verify laws of reflection and refraction.
  20. With the help of a ray diagram, show the formation of image of a point object by refraction of light at a spherical surface separating two media of refractive indices n1and n2(n2> n1) respectively. Using this diagram, derive the relation.What happens to the focal length of convex lens when it is immersed in water?
  21. Define the term dipole moment of an electric dipole indicating its direction. Write its SI unit. An electric dipole is placed in a uniform electric field, Deduce the expression for the torque acting on it. In a particular situation, it has its dipole moment aligned with the electric field. Is the equilibrium stable or unstable?
  22. Obtain the expression for the capacitance of a parallel plate capacitor. Three capacitors of capacitances C1, C2and C3are connected
    1. in series,
    2. in parallel. Show that the energy stored in the series combination is the same as that in the parallel combination.
  23. Define the term magnetic inclination (Dip) and horizontal component of earth’s magnetic field at a place. Establish the relationship between them with the help of a diagram.
  24. Distinguish the magnetic properties of dia, para, and ferromagnetic substances in terms of
    1. susceptibility
    2. magnetic permeability
    3. coercivity. Give one example of each.
  25. Derive a mathematical expression for the force per unit length experienced by each of the two long current carrying conductors placed parallel to each other in air. Hence define one ampere of current. Explain why two parallel straight conductors carrying current in the opposite direction kept near each other in air repel?
  26. With the help of a neat and labelled diagram, explain the underlying principle and working of a moving coil galvanometer. What is the function of:
    1. uniform radial field
    2. soft iron core, in such a device? Write two factors on which the current sensitivity of a moving coil galvanometer depend.
  27. 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.
  28. State the Biot - Savart law for the magnetic field due to a current carrying element. Use this law, obtain a formula for magnetic field
    1. 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.OR
    2. derive the expression for the magnetic field due to a current carrying circular loop of radius 'R', at a point which is at a distance 'x' from its centre along the axis of the loop.
  29. Derive an expression for the torque acting on a loop of N turns, area A, carrying current i, when held in a uniform magnetic field. With the help of circuit, show how a moving coil galvanometer can be converted into an ammeter of given range. Write the necessary mathematical formula.
  30. Derive the expression for the de Broglie wavelength of an electron moving under a potential difference of V volt. Describe Davisson and Germer experiment to establish the wave nature of electrons. Draw a labelled diagram of the apparatus used.
  31. State the principle of working of p-n diode as a rectifier. Explain, with the help of a circuit diagram, the use of p-n diode as
    1. a full wave rectifier
    2. Half wave rectifier. Draw a sketch of the input and output waveforms.
  32. State Bohr’s postulates for an atom? Calculate energy of moving electron for nth orbit? What is the significance of negative energy?
  33. State Gauss’ theorem in electrostatics. Using this theorem, derive the expression for the electric field intensity
    1. at any point outside a uniformly charged thin spherical shell
    2. at a point due to an infinitely long, thin, uniformly charged straight wire
    3. at a point due to an infinite plane sheet of charge.
  34. What is a phasor diagram? With its help, drive an expression for the impedance of an ac series L-c-R circuit. In series LCR circuit, voltage across an inductor, a capacitor and a resistor are 30v, 30v and 60v respectively. What is the phase difference between the applied voltage and current in the circuit.
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Komal & 7 others asked a question
Subject: Physics, asked on on 24/2/14

  1. Draw a labelled ray diagram to show the formation of an image by a compound microscope. Write the expression for its magnifying power. How does the resolving power of a compound microscope change, when
    1. refractive index of the medium between the object and the objective lens increases; and
    2. wavelength of the radiation used is increased?
  2. An electric dipole is held in a uniform electric field.
    1. Using suitable diagram, show that it does not undergo any translatory motion and
    2. derive an expression for the torque acting on it and specify its direction.
  3. Draw a graph to show the variation of the angle of deviation 'D' with that of the angle of incidence 'i' for a monochromatic ray of light passing through a glass prism of refracting angle 'A'. Hence deduce the relation.
  4. Two long parallel straight wires X and Y separated by a distance of 5 cm in air carry currents of 10 A and 5 A respectively in opposite directions. Calculate the magnitude and direction of the force on a 20 cm length of the wire Y.
  5. A circ
  6. circular coil of100 turns, radius 10 cm carries a current of 5 A. it is suspended vertically in a uniform horizontal magnetic field of 0.5 T, the field lines making an angle of 600 with the of the plane of the coil. Calculate of the torque must be applied on it to prevent it from turning.
  7. Two point chargesare located 20 cm apart in vacuum,
    1. Find the electric field at the mid point of the line AB joining the two charges,
    2. If a negative test charge of magnitude 1.5 x10-9c is placed at the centre, find the force experienced by the test charge.
  8. In a given circuit, inductor L and resistor R have identical resistance. Two similar electric lamps B1and B2are connected as shown. When switch S is closed,
    1. which one of the lamps lights up earlier,
    2. will the lamps be equally bright after some time? Justify your answer.
  9. Write the mathematical relation for the resistivity of a material in terms of relaxation time, number density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity of a metal increases and that of a semi-conductor decreases with rise in temperature.
  10. Name the gate obtained from the combination of gates shown in the figure. Draw its logic symbol. Write the truth table of the combination.
  11. Force of attraction between two point charges placed at a distance ‘d’ apart in a medium is ‘F’. What should be the distance in the same medium so that the force of attraction between them becomes 9F ?
  12. Two bulbs whose resistances are in the ratio of 1 : 2, are connected in parallel to a source of constant voltage. What will be the ratio of power dissipation in these?
  13. Write two properties of a material used as a suspension wire in a moving coil galvanometer.
  14. A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time the electric vector is. Calculateat this point.
  15. Define the term ‘activity’ of a radionuclide. Write its SI unit.
  16. At what angle of incidence should a light beam strike a glass slab of refractive - index √3 , such that the reflected and the refracted rays are perpendicular to each other ?
  17. A carrier wave of peak voltage 12 V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75 %?
  18. Which mode of propagation is used by short wave broadcast services having frequency range from a few MHz up to 30 MHz?
  19. Derive an expression for the energy stored in a charged parallel plate capacitor with air as the medium between its plates.
  20. A bar magnet of magnetic moment 1.5 J/T lies aligned with the direction of a uniform magnetic field of 0.22 T.
  21. What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment,normal to the field direction, & Opposite to the field direction?

Priyanka & 2 others asked a question
Subject: Physics, asked on on 21/2/16

Physics

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Numerical Questions(2 marks)

  1. The output of an OR gate is connected to both the inputs of a NAND gate. Draw the logic circuit of this combination of gates and write its truth table.
  2. A convex lens of refractive index 1.5 has a focal length of 18 cm in air. Calculate the change in its focal length when it is immersed in water of refractive index 1.33.
  3. Two point charges and are separated by a distance of 1 m in air. Calculate at what point on the line joining the two charges is the electric potential zero.
  4. A voltage of 30 V is applied across a carbon resistor with first, second and third rings of blue, black and yellow colours respectively. Calculate the value of current, in mA, through the resistor.
  5. Calculate the current drawn by the primary of a transformer which steps down 200 V to 20 V to operate a device of resistance. Assume the efficiency of the transformer to be 80%.
  6. An a.c. voltage of 100 V, 50 Hz is connected across a 20 ohm resistor and mH inductor in series. Calculate
    1. impedance of the circuit,
    2. rms current in the circuit
  7. In an ammeter (consisting of a galvanometer and a shunt), 0.5% of the main current passes through the galvanometer. Resistance of the galvanometer coil is G. Calculate the resistance of the shunt in terms of galvanometer resistance, G.
  8. An electric bulb B and a parallel plate capacitor C are connected in series to the a.c. mains as shown in the given figure. The bulb glows with some brightness. How will the glow of the bulb be affected on introducing a dielectric slab between the plates of the capacitor? Give reasons in support of your answer.
  9. The output of a 2-input NOR gate is fed to a NOT gate. Draw the logic circuit of this combination of gates and write the truth table for the output of the combination for all inputs.
  10. The electric field and electric potential at any point due to a point charge kept in air is 20 N/C and 10 J/C respectively. Compute the magnitude of this charge.
  11. Draw and explain the output waveform across the load resistor R, if the input waveform is as shown in the given figure.
  12. Two cells E1 and E2 in the given circuit diagram have an emf of 5 V and 9 V and internal resistance of 0.3Ω and 1.2Ω respectively.
  13. Calculate the value of current flowing through the resistance of 3Ω.
  14. Two capacitors of capacitance of 6µF and 12µF are connected in series with a battery. The voltage across the 6µF capacitor is 2 V. Compute the total battery voltage.
  15. A parallel plate capacitor with air between the plates has a capacitance of 8 pF. The separation between the pates is now reduced by half and the space between them is filled with a medium of dielectric constant 5. Calculate the value of capacitance of the capacitor in the second case.
  16. A 4µF capacitor is charged by a 200 V supply. The supply is then disconnected and the charged capacitor is connected to another uncharged 2 µF capacitor. How much electrostatic energy of the first capacitor is lost in the process of attaining the steady situation?
  17. Find the wavelength of electromagnetic waves of frequency 5 x 1019Hz in free space.
  18. A compound microscope with an objective of 1.0 cm focal length and an eye-piece of 2.0 cm focal length has a tube length of 20 cm. Calculate the magnifying power of the microscope, if the final image is formed at the near point of the eye.
  19. The magnifying power of an astronomical telescope in the normal adjustment position is 100. The distance between the objective and the eye-piece is 101 cm. Calculate the focal lengths of the objective and of the eye-piece.
  20. An electric dipole of length 4 cm, when placed with its axis making an angle of 600 with a uniform electric field experiences a torque 4√3 Nm. Calculate the
    1. magnitude of the electric field.
    2. potential energy of the dipole, if the dipole has charges of ±8nC.
  21. ATV tower has a height of 400 m at a given place. Calculate coverage range, if the radius of the earth is 6400 km.
  22. Give the logic symbol for an OR gate. Draw the output wave form for input wave forms A and B for this gate.
  23. In the figure below, circuit symbol of a logic gate and input wave from is shown.
    1. Name the logic gate,
    2. write its truth table and
    3. give the output wave form.
  24. Two point charges qA= +3µc and qB= -3µc are located 20 cm apart in vacuum,
    1. Find the electric field at the mid -point of the line AB joining the two charges,
    2. If a negative test charge of magnitude1.5×10-9Cis placed at the centre, find the force experienced by the test charge.
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Subject: Physics, asked on on 8/11/13
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Subject: Physics, asked on on 25/2/14
  1. Explain, using Huygens’ principle ,how diffraction is produced by a narrow slit which is illuminated by monochromatic light. Show that central maximum is twice as wide as the other maxima and the pattern becomes narrower as the width of the slit is increased.
  2. explane
    1. State Brewster’s law.
    2. A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length 6.0 cm. What is the magnifying power of the telescope ? What is the separation between the objective and the eyepiece ?
  3. What is the significance of Davisson and Germer experiment. Draw Davisson- Germer 3 electron diffraction arrangement. Where do we find the utility of the result of the experiment ?
  4. Draw a diagram to show the variation of binding energy per nucleon with mass number for different nuclei. State with reason why light nuclei usually undergo nuclear fusion.
  5. A 10 kg satellite circles earth once every 2 h in an orbit having a radius of 8000 km. Assuming that Bohr’s angular momentum postulate applies to satellites just as it does to an electron in the hydrogen atom , find the quantum number of the orbit of the satellite.
  6. A ground receiver station is receiving a signal at
    1. 5 MHz and
    2. 100 MHz transmitted from a ground transmitter at a height of 300 m located at a distance of 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder.
    ( Given the value of radius of the earth is 6400 km and maximum electron density, Nmax=1012m-3)
  7. Explain
    1. forward biasing
    2. Reverse biasing of the p-n junction diode .With the help of a circuit diagram, explain the use of this device as a half-wave rectifier.
  8. A parallel plate capacitor, each with plate area A and separation d, is charged to a potential difference V. The battery used to charge it is then disconnected. A dielectric slab of thickness d and dielectric constant k is now placed between the plates. What change, if any, will take place in :
    1. charge on plates,
    2. electric field intensity between the plates
    3. capacitance of the capacitor. Justify your answer in each case.

    OR

    1. State the principle of Van de Graaff generator and draw a labelled diagram of the generator.
    2. A parallel plate capacitor is to be designed with a voltage rating 1 kV, using a material of dielectric constant 3 and dielectric strength about 107 Vm-1. For safety ,we would like the field never to exceed say 10% of the dielectric strength. What minimum area of the plates is required to have a capacitance of 50 pF ?
    1. Derive an expression for the maximum force experienced by a straight conductor of length l, carrying current I and kept in a uniform magnetic field B.
    2. A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspended in mid-air by a uniform horizontal magnetic field B. What is the magnitude of the magnetic field

    OR

    1. State the principle of cyclotron and draw labelled diagram.
    2. A cyclotron’s oscillator frequency is 10 MHz .What should be the operating magnetic field for accelerating protons ? If the radius of the ‘Dees’ is 60 cm, what is the kinetic energy of the proton beam produced by the accelerator ? (e=1.60 x 10-19C,mp=1.67 x 10-27kg ). Express your answer in units of MeV ( 1 MeV =1.602 x 10-13J)
  9. Draw a labelled ray diagram of an astronomical telescope, forming the image at infinity. An astronomical telescope uses two lenses powers 10 dioptre, 1 dioptre.
    1. State with reason, which lens is preferred as objective and eye-piece.
    2. Calculate the magnifying power of the telescope ,if the final image is formed at the near point.
    3. How do the light gathering power and resolving power of a telescope change if the aperture of the objective lens isdoubled ?

    OR

    1. An angular magnification (magnifying power) of 30 is desired using an objective of focal length 1.25 cm and an eyepiece of focal length 5 cm. How will you set up the compound microscope ?
    2. A myopic person has been using spectacles of power -1.0 dioptre for distant vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened .

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  1. What is the De Broglie wavelength associated with
    1. an electron moving with a speed of 5.4×106m/s, and
    2. a ball of mass 150g travelling at 30.0 m/s?
  2. The half-life of92U238undergoing α- decay is 4.5×109years. What is the activity of 1g sample of92U238?
  3. A regular hexagon of side 10 cm has a charge 5µc at each of its vertices. Calculate the potential at the centre of the hexagon.
  4. Double convex lenses are to be manufactured from a glass of refractive index 1.55 with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?
  5. Three capacitors of capacitance 2pF, 3pF and 4pF are connected in parallel.
    1. What is the total capacitance of the combination?
    2. Determine the charge on each capacitor if the combination is connected to a 100V supply.
  6. What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens?
  7. Fig. shows a light bulb (B) and iron cored inductor connected to a DC battery through a switch (S).
    1. What will one observe when switch (S) is closed?
    2. How will the glow of the bulb change when the battery is replaced by an ac source of rms voltage equal to the voltage of DC battery? Justify your answer in each case.
  8. The given figure shows the experimental set up of a metre bridge. The null point is found to be 60cm away from the end A with X and Y in position as shown.

    When a resistance of 15Ω is connected in series with ‘Y’, the null point is found to shift by 10cm towards the end A of the wire. Find the position of null point if a resistance of 30Ω were connected in parallel with ‘Y’.
  9. Why is a potentiometer preferred over a voltmeter for determining the emf of a cell? Two cells of emf E1and E2are connected together in two ways shown here.

    The 'balance points' in a given potentiometer experiment for these two combinations of cells are found to be at 351.0cm and 70.2cm respectively. Calculate the ratio of the emfs of the two cells.

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