**Problem 1: **What is the magnitude of the force of attraction between an iron nucleus bearing charge +26e and its innermost electron, if the distance between them is 1.0 × 10^{-12}m? See Solution

**Problem 2:** Charges 2µC, 3µC and 4µC are place in air at the vertices of an equilateral triangle of sides 10 cm. What is the magnitude of the resultant force acting on the 4µC charge? See Solution

**Problem 3:** A charge q is placed at the center of a line joining two charges each of magnitude Q. Prove that the system of three charges will be in equilibrium if q = -Q/4. See Solution

**Problem 4: **Two opposite charges of magnitude 2 × 10^{-7} are placed 15 cm apart. What is the magnitude and direction of electric intensity (E) at a point mid-way between the charges? What force would act on a proton placed there? See Solution

**Problem 5:** Two positive point charges of 15 × 10^{-10}C and 13 × 10^{-10}C are placed 12 cm apart. Find the work done in bringing the two charges 4 cm closer. See Solution

**Problem 6:** A hallow sphere is charged to 14 µC. Find the potential (a) at its surface (b) inside the sphere (c) at a distance of 0.2 m from its surface. The radius of the sphere is 0.3 m. See Solution

**Problem 7: **If 280 J of work is done in carrying a charge of 2 C from a place where the potential is -12 V to another place where potential is V. Calculate the value of V. See Solution

**Problem 8:** Calculate the electric potential at the surface of a silver nucleus having radius 3.4 × 10^{-14} m. The atomic number of silver is 47 and charge on proton is 1.6 × 10^{-19}C. See Solution

**Problem 9: **The electric field at a point due to a point charge is 26 N/C and the electric potential at that point is 13 J/C. Calculate the distance of the point from the charge and magnitude of the charge. See Solution

**Problem 10:** Two point charges of 8µC and -4µC are separated by a distance of 10 cm in the air. At what point on the line joining the two charges is the electric potential zero? See Solution

**Problem 11:** An electron with an initial speed of 29 × 10^{5} m/s is fired in the same direction as a uniform electric field of 80 N/C. How far does the electron travel before brought to rest and turned back? See Solution

**Problem 12:** Two capacitors of capacitances 4µF and 8 µF are first connected (a) in series and then (b) in parallel. In each case external voltage source is 200 V. Calculate in each case the total capacitance, the potential drop across each capacitor and charge on each capacitor. See Solution

**Problem 13:** Three capacitors of capacitances 4 µF, 6 µF and 8 µF respectively are connected in series to a 250 V d.c supply. Find (1) the total capacitance (2) charge on each capacitor (3) P D across each capacitor. See Solution

**Problem 14:** If C_{1} = 14 µF, C_{2} = 20 µF and C_{3} = 12 µF and the insulated plate of C_{1} be at a potential 100V while one plate of C_{3} being earthed. What is the potential difference between the plates of C_{2} when the three capacitors are connected in series? See Solution

**Problem 15:** Find the charge on 5 µF capacitor in the circuit shown:

**Problem 16:** Two parallel plate capacitors A and B having capacitance of 2 µF and 6 µF are charged seperately to the same potential of 120 V. Now positive plate of A is connected to the negative plate of B and the negative plate of A is connected to the positive of B. Find the final charges on each capacitor.

**Problem 17:** A 6 µF capacitor is charged to a P.D 120 V and then connected to an uncharged 4 µF capacitor. Calculate the P.D across the capacitors.

**Problem 18:** Two capacitors of capacitance 8 µF and 10 µF are connected in series to a source of P.D of 180 V. The capacitors are disconnected from the supply and are connected in parallel with each other. Find the new potential difference and charge on each capacitor.

## Solved numerical problems from the book.

- Problem 11.2: Two small spheres each having a mass of 0.1 g are suspended from a point through the threads 20 cm long. They are equally charged and repel each other to a distance of 24 cm. What is the charge on each sphere? See Solution
- Problem 11.1: Find electric field at a distance of 30 cm from a 3 micro C point charge. See Solution
- Problem 11.3: A metallic sphere of 30 cm diameter carries a charge of 600 micro C. Find the electric field intensity (a) at a distance of 50 cm from the center of the sphere and (b) at the surface of the sphere. See Solution
- What is the electric potential energy of a 7 nC charge that is 2 cm from a 20 nC charge? See Solution
- What is the potential difference between two points in an electric field if it takes 600 J of energy to move a charge of 2 C between these two points? See Solution

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