NCERT Solutions for class 12 Physics Chapter 1
Answer The Following Question Answers of class 12 physics Chapter 2 – Electrostatic Potential and Capacitance:
Question 1. Two charges 5 × 10−8 C and −3 × 10−8 C are located 16 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero. Solution : Given, Two charges q A = 5 x 10 -8 C and q B = -3x10 -8 C Distance between two charges, r = 16 cm = 0.16 m Consider a point O on the line joining two charges where the electric potential is zero due to two charges. Question 2. A regular hexagon of side 10 cm has a charge 5 µC at each of its vertices. Calculate the potential at the centre of the hexagon. Solution : Let O be the center of the hexagon. It contains the charges at all its 6 vertices, each charge = + 5 μC = 5×10 -6 C. The side of the hexagon is 10 cm = 0.1 m It follows that the point O, when joined to the two ends of a side of the hexagon forms an equilateral triangle Electric potential at O due to one charge, Question 3. Two charges 2 μC and −2 µC are placed at points A and B 6 cm apart. (a) Identify an equipotential surface of the system. (b) What is the direction of the electric field at every point on this surface? Solution : (a) For the given system of two charges, the equipotential surface will be a plane normal to the line AB joining the two charges and passing through its mid-point O. On any point on this plane, the potential is zero. (b) The electric field is in a direction from the point A to point B i.e. from the positive charge to the negative charge and normal to the equipotential surface. Question 4. A spherical conductor of radius 12 cm has a charge of 1.6 × 10−7C distributed uniformly on its surface. What is the electric field (a) Inside the sphere (b) Just outside the sphere (c) At a point 18 cm from the centre of the sphere? Solution : Given, q = 1.6 x 10 -7 C Radius of the sphere, r = 12 cm = 0.12 m(a) Inside the sphere: The charge on a conductor resides on its outer surface. Therefore, electric field inside the sphere is zero.
(b) Just outside the sphere: For a point on the charged spherical conductor or outside it, the charge may be assumed to be concentrated at its center.
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Question 5. A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10−12 F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6? Solution : Given: Capacitance of capacitor when medium between two plates is air, C = 8 pF = 8×10 –12 F Question 6. Three capacitors each of capacitance 9 pF are connected in series. (a) What is the total capacitance of the combination? (b) What is the potential difference across each capacitor if the combination is connected to a 120 V supply? Solution : Given, C 1 = C 2 = C 3 = 9 pF = 9 x 10 -12 F V = 120 volt . Question 7. Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. (a) What is the total capacitance of the combination? (b) Determine the charge on each capacitor if the combination is connected to a 100 V supply. Solution : Given, C 1 = 2 pF C 2 = 3 pF C 3 = 4 pF , V = 100 volt