**ELECTROSTATICS : Questions**

Assam Board Questions on Electrostatics:

**These questions are from past exams of Higher Secondary final under AHSEC, Assam:**

** ****Q1) [HS ’12]** Can a body have a charge of 1.8x10^{-19} C? Give reason. [marks 1]

**Q2) [HS ’13]** State Gauss’s Law of electrostatics. [marks 1]

**Q3) [HS ’12]** Using Gauss’s theorem find the field due to a charged thin spherical shell at a point outside the shell. [Marks 2]

**Q4) [HS ’12]** Find an expression for electric field at any position on an axial line of an electric dipole. [Marks 2]

**Q5) [HS ’13]** What is an electric dipole? Find an expression for the torque acting on an electric dipole placed in an external uniform electric field. [Marks 1+1=2]

**Q6) [HS ’13]** If electric field E = 0 in a region do you think potential at the region should also be zero? Justify your answer. [Marks 2]

**Q7) [HS ’13]** What is electrostatic shielding? How can it be achieved? [Marks 1+1=2]

**Q8) [HS ’14]** State Coulomb’s law of electrostatics. Express it in vector form. [Marks 1+1=2]

**Q9) [HS ’14]** Apply Gauss’s theorem to calculate the electric field due to an infinite plane sheet of charge. [Marks 3]

**Q10) [HS ’14]** If E = (3i + 6j + 4k) N/C, calculate the electric flux through a surface of area 20 cm^{2} in Y-Z plane. [Marks 3]

**Q11) [HS ’12]** A condenser of capacity 500 pF is charged to a potential 100V. Find the charge on the condenser and energy stored in it. [Marks 2]

**Q12) [HS ’13]** Find an expression for potential at a point due to a point charge. [Marks 2]

**Q13) [HS ’13]** A 400 pF capacitor is charged by a 100V Battery. How much electrostatic energy is stored by the capacitor? [Marks 2]

**Q14) [HS ’14]** What is electric polarization vector? Define the electric susceptibility. [Marks 1+1=2]

**Q15] [HS ’14]** Deduce an expression for the capacity of a parallel plate condenser. [Marks 3]

**Q)[HS’15, Marks=1]** What is quantisation of charge?

**Answer:** The fact that electric charge is always an integral multiple of e (the charge on an electron) is called quantisation of charge.

**Q)[HS’15, Marks=2]** A 100pF capacitor is charged by a potential difference of 100V. What is the amount of charge stored? What is the electrostatic energy stored in the capacitor?

**Q)[HS’15, Marks=5] **Define electric dipole and dipole moment. Derive an expression for electric field intensity at a point on the axial line of an electric dipole.

**Answer:** An electric dipole is defined as a pair of equal and opposite point charges separated by a small distance.

Electric dipole moment is a measure of the strength of the dipole. It is vector quantity whose magnitude is equal to the product of one of the charges and the distance between them.

Mathematically, dipole moment p = q(2a)

The direction of the dipole moment is from the negative charge to the positive charge.

[The derivation is same as the question of HS’12 above.]

**Q)[HS’15, Marks=5]** Explain the concept of electric field. Express electric flux through a surface in terms of electric field intensity. Show that the electric flux through a cylindrical surface with its axis parallel to a uniform electric field is zero.

**Q)[HS’16, Marks=2] **State two basic properties of electric charges.

**Q)[HS’16, Marks=2] **Define dielectric constant of a medium.

**Q)[HS’16, Marks=3] **A parallel plate capacitor has plate separation d and the area of each plate is A. The space between the plates is completely filled with a dielectric of constant K. Derive the expression for the capacity of the parallel plate capacitor.

**Q)[HS’17, Marks=1]** In an electric field a unit positive charge is displaced from one point to another point along a straight line of length 2 cm and the work done is 2 mJ. If it is displayed along a parabolic path between the same points of length 5 cm, what will be the work done?

**Q)[HS’17, Marks=2]** Three electric point charges q0, q1 and q2 are at distances r0, r1 and r2 respectively with respect to same origin. What is the force on charge q0 in the field of charges q1 and q2?

**Q)[HS’17, Marks=2] **The volume charge density within a volume V is (r). What is the force on a small test charge qo placed outside the volume having position vector r0 with respect to the same origin considered to specify the position vector of the charge distribution within the volume?

**Q)[HS’17, Marks=1+3+1] **What is the net electric flux through a closed surface surrounding an electric dipole? Derive the expressions for electric field intensity both inside and outside a uniformly charged spherical shell. What is the total charge enclosed by a closed surface if the electric flux entering and leaving the surface are 20000 N/C m2 and 30000 N/C m2 respectively? Given ε0=8.35x10-12C2N-1m-2

**Q)[HS’17, Marks=1+1+1+2] **Why is an insulator sometimes called a dielectric? What is the main difference between free and bound charge? Generally, one of the two plates of a Capacitor system is earthed, why? Derive the expression for the energy stored in a charged capacitor.

**Q)[HS’18, Marks=1] **Which experiment established the fact that electric charge is quantized?

**Answer:** Millikan’s Oil Drop experiment established the fact that electric charge is quantized.

**Q)[HS’18, Marks=1+1]** Give the statement of Coulomb’s law for the force between two point charges. Write this law in vector notation for two point charges of same magnitude and opposite sign separated by a distance r in vacuum.

**Q)[HS’18, Marks=1+1]** Two point charges 0.01 C are placed 10 cm apart in vacuum. Calculate the magnitude of electric field intensity at the middle point of the charges and mention its direction.

**Q)[HS’18, Marks=3] **A 600 pF capacitor is charged by a 200V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor. How much electrostatic energy is lost in the process?