Wednesday, October 11, 2006

Two Kerala Entrance 2006 Questions on Electrostatics


The following mcq appeared in the Kerala Engineering Entrance
Test 2006 question paper:
A network of six capacitors, each of value C, is made as shown in Fig 1. The quivalencapacitance between the points A and B is
(a) C/4 (b) 3C/4 (d) 3C/2 (d) 3C (e) 4C/3
The network shown in Fig 1 is redrawn in the second figure shown side by side with Fig1. You can easily understand that the network has two identical branches, each containing a parallel combination of two capacitors in series with a single capacitor.The parallel combined value 2C in series with C makes a net value 2C.C/(2C+C) = 2C/3. The parallel combined value of the two branches is the equivalent capacitance between A and B and is equal to 4C/3 [Option (e)].
The following mcq appeared in the Kerala Medical Entrance Test 2006 question paper:
The total electrical flux leaving a spherical surface of radius ‘r’ metre enclosing an electric dipole of charge ‘q’ is
(a) zero (b) q/ε0 (c) 8π
r2q/ε0 (d) 2q/ε0 (e) 4π r2q/ε0

This is a very simple question which you will occasionally get. Since the closed surface contains a dipole, the electric flux leaving the surface is zero. Note that the outward flux due to the positive charge of the dipole is balanced by the inward flux due to the negative charge of the dipole.

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