Class XII Physics Sample Question Paper

Answer: Electric dipole moment is defined as the product of magnitude of either charge and the distance between the two charges. Its SI unit is coulomb-meter (Cm).

Answer: Drift velocity is the average velocity with which free electrons get drifted in a conductor under the influence of an electric field.

Answer: Gauss's law states that the total electric flux through any closed surface (called Gaussian surface) is equal to (1/) times the total charge enclosed by the surface.

Proof: Consider a point charge q at the center. Draw a sphere of radius r around it. The electric field at all points on the sphere is E = (1/4)(q/r). The flux through the sphere is = E 4r = (1/4)(q/r) 4r = q/.

Answer: Consider two parallel conductors carrying currents I and I, separated by distance r. The magnetic field produced by I at the location of I is B = (/4)(2I/r). The force per unit length on conductor 2 is F = I B = I (/4)(2I/r) = (/2)(II/r). This gives the attractive force between conductors carrying currents in the same direction.

Answer: Consider a concave mirror with focus F and center of curvature C. Let an object be placed at point O. Using ray diagrams and geometry, we can derive the mirror formula: 1/f = 1/v + 1/u, where f is the focal length, v is the image distance, and u is the object distance. This formula relates object distance, image distance, and focal length for spherical mirrors.

Answer: A potentiometer works on the principle that the potential drop across a uniform wire is directly proportional to its length when a constant current flows through it. To compare the emf of two cells, we first connect one cell (E) to the potentiometer and find the balancing length l. Then replace it with the second cell (E) and find the new balancing length l. Since the potential drop per unit length remains constant, we have E/E = l/l, allowing us to compare the emf of the two cells.

Answer: a) Voltage fluctuation refers to the continuous change in voltage level above or below the normal range. It can damage electronic appliances and reduce their lifespan.

b) A voltage stabilizer maintains the output voltage at a desired level despite changes in input voltage. It consists of an autotransformer with multiple taps and electronic circuits that detect voltage changes and automatically select the appropriate tap.

c) Rajan's father shows values of responsibility towards family welfare, knowledge-sharing, and practical application of technical skills to solve real-life problems.

Answer: a) When charging a capacitor, work is done to move charge from one plate to another against the electric field. The potential difference across the capacitor is V = Q/C. The work done in moving a small charge dq against potential difference V is dW = Vdq = (q/C)dq. Integrating from 0 to Q, we get W = ^Q (q/C)dq = Q/(2C). This work done is stored as potential energy: U = Q/(2C) = CV = QV.

b) For a parallel plate capacitor, C = A/d. When the distance is halved (d' = d/2) and the space is filled with a dielectric (k = 6), the new capacitance C' = kA/d' = 6A/(d/2) = 12A/d = 12C. Substituting C = 8 pF, we get C' = 12 8 pF = 96 pF.