$4$(a) (i) Explain the following statements giving reason : (I) An equipotential surface through a point is normal to the electric field at that point. (II) When a dielectric is placed in an external electric field, the electric field inside the dielectric is less than that outside it. (III) The potential difference between the plates of a charged parallel plate capacitor decreases when its plates are brought closer. (ii) Obtain an expression for the work done to dissociate the system of three charges q, - 4q and 2q placed at the vertices A, B and C respectively of an equilateral triangle of side 'a'.

OR

(b) (i) Answer the following giving reason : (I) The electron drift speed is estimated to be only a few mm/s for currents in the range of a few amperes. How, then, is the current established almost the instant a circuit is closed ? (II) A low voltage supply from which one needs high currents must have very low internal resistance. Why ? (III) The assertion that V = IR is a statement of Ohm's law is not true. Why ? (ii) Two cells of emfs 12 V and 6 V are connected in parallel as shown in the figure. Their internal resistances are $\displaystyle 1 \Omega$ and $\displaystyle 0.5 \Omega$ respectively. Calculate the emf and internal resistance of the equivalent cell between points A and B. 2026_CBSE_Physics_Set_Region4_Subset_Set1_QUNKNOWN__ii_p16_6

2026_CBSE_Physics_Set_Region4_Subset_Set1_QUNKNOWN__ii_p16_6

Physics · Electrostatic Potential and Capacitance · Equipotential Surfaces