Section A
Q1.
(a) Find y(0.75) by applying Euler's method to the initial value problem (dy)/(dx) = 2 cos(4π x)/(3)) - y, y(0) = 1. Take step size h = 0.25.
(b) Four charges q1 = -2.0 × 10-9 Coulomb, q2 = 3.0 × 10-9 Coulomb, q3 = 2.0 × 10-9 Coulomb and q4 = 1.0 × 10-9 Coulomb are placed at four corners of a square of 2.0 metre side. Find out the potential at the centre of the square.
(c)
(i) Discuss the biasing conditions of p-n junctions in a Bipolar Junction transistor under saturation and cut off conditions.
(ii) Determine whether the transistor circuit shown can be termed as being saturated.
(d) Two parallel plates are separated 0.25 cm apart. The gap is partially filled with 0.23 cm thick sheet of fibre with \epsilonr = 5. A potential difference of 2.5 KV is applied across the plate. Determine the electric field strength in the fibre and air film between the fibre and the plate. Will the air break down? Dielectric strength of air can be taken as 30 KV/cm.
(e)
(i) What is meant by the term pinch off voltage of a JFET? Draw the drain characteristics of a JFET for V_{GS} = 0 V & show the pinch off voltage in the diagram.
(ii) Define the terms transconductance and amplification factor of a JFET.
(iii) In an FET, as V_{GS}, the gate-to-source voltage is varied from -1.5 V to -2 V, keeping V_{DS} constant, I_D of an FET decreases from 7.5 mA to 5.5 mA. What is the transconductance of the FET? If the a.c. drain resistance is 210 kilo ohms, find the amplification factor.
