12th

12th Standard EM

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Physics

use black pen only
Time : 02:00:00 Hrs
Total Marks : 50
    part-A
    10 x 1 = 10
  1. An electric field \(\vec { E } =10x\hat { i } \) exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

    (a)

    10 J

    (b)

    -20 J

    (c)

    +20 J

    (d)

    -10 J

    1. Rank the electrostatic potential energies for the given system of charges in increasing order.

      (a)

      1 = 4 < 2 < 3

      (b)

      2 = 4 < 3 < 1

      (c)

      2 = 3 < 1 < 4

      (d)

      3 < 1 < 2 < 4

    1. An electric dipole is placed at an alignment angle of 300 with an electric fi eld of 2 × 105 NC-1. It experiences a torque equal to 8 N m. Th e charge on the dipole if the dipole length is 1 cm is

      (a)

      4 mC

      (b)

      8 mC

      (c)

      5 mC

      (d)

      7 mC

    2. Four Gaussian surfaces are given below with charges inside each Gaussian surface. Rank the electric fl ux through each Gaussian surface in increasing order.

      (a)

      D < C < B < A

      (b)

      A < B = C < D

      (c)

      C < A = B < D

      (d)

      D > C > B > A

    1. Two identical point charges of magnitude –q are fi xed as shown in the fi gure below. A third charge +q is placed midway between the two charges at the point P. Suppose this charge +q is displaced a small distance from the point P in the directions indicated by the arrows, in which direction(s) will +q be stable with respect to the displacement

      (a)

      A1 and A2

      (b)

      B1 and B2

      (c)

      both directions

      (d)

      No stable

    2. What is the ratio of the charges \(\left| \frac { { q }_{ 1 } }{ { q }_{ 2 } } \right| \) for the following electric field line pattern?

      (a)

      \(\frac { 1 }{ 5 } \)

      (b)

      \(\frac { 25 }{ 11 } \)

      (c)

      5

      (d)

      \(\frac { 11 }{ 25 } \)

  2. Odd one out
    * * *
  3. (a) Electric dipole moment
    (b) Electric field intensity
    (c) Electric potential difference
    (d) Electrostatic shielding

  4. (a) Mica
    (b) Ebonite
    (c) Aluminium
    (d) Oil

  5. Choose the correct pair
    * * *
    1. Which charge configuration produces a uniform electric field?

      (a)

      point Charge

      (b)

      infinite uniform line charge

      (c)

      uniformly charged infinite plane

      (d)

      uniformly charged spherical shell

    2. The total electric fl ux for the following closed surface which is kept inside water

      (a)

      \(\frac { 80q }{ { \varepsilon }_{ 0 } } \)

      (b)

      \(\frac { q }{ { 40\varepsilon }_{ 0 } } \)

      (c)

      \(\frac { q }{ { 80\varepsilon }_{ 0 } } \)

      (d)

      \(\frac { q }{ { 160\varepsilon }_{ 0 } } \)

    3. A thin conducting spherical shell of radius R has a charge Q which is uniformly distributed on its surface. The correct plot for electrostatic potential due to this spherical shell is

      (a)

      (b)

      (c)

      (d)

  6. part-B

    Answer any three of the following

    3x4=12
  7. What is meant by quantisation of charges?

  8. Write down Coulomb’s law in vector form and mention what each term represents.

  9. What are the differences between Coulomb force and gravitational force?

  10. Write a short note on superposition principle.

  11. Define ‘Electric field’.

    1. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be

      (a)

      less than before

      (b)

      same as before

      (c)

      more than before

      (d)

      zero

  12. Part-C
    5 x 3 = 15
  13. Calculate the number of electrons in one coulomb of negative charge.

  14. Consider two point charges q1 and q2 at rest as shown in the figure.

    They are separated by a distance of 1m. Calculate the force experienced by the two charges for the following cases:
    (a) q1 = +2μC and q2 = +3μC
    (b) q1 = +2μC and q2 = -3μC
    (c) q1= +2μC and q2 = -3μC kept in water (εr = 80)

    1. Calculate the electrostatic force and gravitational force between the proton and the electron in a hydrogen atom. They are separated by a distance of 5.3 × 10-11 m. The magnitude of charges on the electron and proton are 1.6 × 10-19 C. Mass of the electron is me = 9.1 × 10-31 kg and mass of proton is mp = 1.6 × 10-27 kg.

    1. Consider the charge configuration as shown in the figure. Calculate the electric field at point A. If an electron is placed at points A, what is the acceleration experienced by this electron? (mass of the electron = 9.1 × 10-31 kg and charge of electron = −1.6 × 10-19 C)

    1. Calculate the electric field at points P, Q for the following two cases, as shown in the figure.
      (a) A positive point charge +1 μC is placed at the origin.
      (b) A negative point charge -2 μC is placed at the origin.

  15. Part-D
    3 x 5 = 15
  16. Consider a point charge +q placed at the origin and another point charge -2q placed at a distance of 9 m from the charge +q. Determine the point between the two charges at which electric potential is zero.

  17. The following figure represents the electric potential as a function of x – coordinate. Plot the corresponding electric field as a function of x.

  18. Four charges are arranged at the corners of the square PQRS of side a as shown in the figure.(a) Find the work required to assemble these charges in the given configuration. (b) Suppose a charge q′ is brought to the center of the square, by keeping the four charges fixed at the corners, how much extra work is required for this?
     

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