## F.Sc ICS Notes: Physics XII: Chapter 12 Electrostatics Numerical Problems

__Compare magnitudes of electrical and gravitational force exerted on an object (mass 20 g charge = 20 micro C) by an identical object that is placed 10 cm from the first. (G = 6.67 * 10(-11) Nm(2)kg(-2))__

**Numerical Problem 12.1:**__Calculate the net electrostatic force on q as shown in the figure on book.__

**Numerical Problem 12.2**__A point charge q = -8 * 10(-8) C is placed at the origin. Calculate electric field at a point 2 m from the origin on the z axis?__

**Numerical Problem 12.3**__Determine the electric field at the position r = (4i + 3j) m caused by as point charge q = 5 * 10(-6) placed at origin.__

**Numerical Problem 12.4**__Two point charges, q1 = -1 * 10(-6) C and q2 = 4 * 10(-6) C, separated by a distance of 3 m. Find and justify the zero field location.__

**Numerical Problem 12.5**__Find the electric field strength required to hold suspended particle of mass 1 * 10(-6) kg and charge 1 micro C between two plates 10 cm apart.__

**Numerical Problem 12.6**__A particle having a charge of 20 electrons on it falls through a potential difference of 100 volts. Calculate the energy acquired by it in electron volts (eV).__

**Numerical Problem 12.7**__In Millikan's experiment, oil droplets are introduced into the space between two flat horizontal plates, 500 mm apart. The plate voltage is adjusted to exactly 780 Volts so that the droplet is held stationary. The plate voltage is switched off and the selected droplet is observed to fall a measured distance of 1.50 mm in 11.2 s. Given that the density of the oil used is 9000kgm(-3), and the viscosity of air at laboratory temperature is 1.8 * 10(-5) Nm(-2)s, calculate:__

**Numerical Problem 12.8****(a)**the mass, and

**(b)**the charge on the droplet (assume g = 9.8 ms(-2))

__A proton placed in uniform electric field of 5000 NC(-1) directed to right is allowed to go a distance of 10 cm from A to B. Calculate:__

**Numerical Problem 12.9****(a)**Potential difference between the two points

**(b)**Work done

**(c)**The change in Potential Energy of the proton

**(d)**The change in Kinetic Energy of the proton

**(e)**Its velocity (mass of proton is 1.67 * 10(27) kg)

__Using zero reference point at infinity, determine the amount by which a point charge of 4 * 10(-8) C alters the electric potential at point 1.2m away, when__

**Numerical Problem 12.10****(a)**charge is positive

**(b)**charge is negative

__In Bohr's atomic model of hydrogen atom, the electron is in an orbit around the nuclear proton at a distance of 5.29 * 10(-11) m with a speed of 2.18 8 10(6) m/s.__

**Numerical Problem 12.11****(a)**The electric potential that a proton exerts at this distance.

**(b)**Total energy of the atom in eV.

**(c)**The ionization energy for the atom in eV.

__The electrostatic flash attachment for a camera contains a capacitor for storing energy used to produce the flash. In one such unit, the potential difference between the plates of a 750 micro Farad capacitor is 330 Volt. Determine the energy that is used to produce the flash.__

**Numerical Problem 12.12**__A capacitor has a capacitance of 2.5 * 10(-8) Farad. In the changing process, electrons removed from one plate and placed on the other one. When the potential difference between the plates is 450 volt, how many electrons have been transferred? (e = 1.60 * 10(-19) Coulomb)__

**Numerical Problem 12.13**
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