# Electronics and Communication Engineering - Exam Questions Papers

46.
A sphere with charge Q was placed in, but not touching a larger hollow sphere. If there is any charge initially on the outer sphere; to remove it the outer sphere was earthed momentarily, and then the inner sphere was removed. The charge remaining on the outer sphere was then measured. This charge was found to be __________ to the charge on the inner sphere.
equal and of same again
equal and of opposite sign
unequal and of same sign
unequal and of opposite sign
Explanation:

This is true for all sizes of the spheres and for all types of dielectric media between the spheres.

47.
At t = ∞; VR2 and VC will be
4, 4
2, 4
0, 2
2, 0
Explanation:

When steady state is reached again; then C is open

Now VR2 = 2V

.

48.
Two products are sold from a vending machine, which has two push buttons P1 and P2. When a button is pressed, the price of the corresponding product is displayed in a 7-segment display. If no buttons are pressed, '0' is displayed, signifying 'Rs' .0'. If only P1 is pressed, '2' is displayed, signifying 'Rs. 2'.
If only P2 is pressed, '5' is displayed, signifying 'Rs. 5'.
If both P1 and P2 are pressed, 'E' is displayed, signifying 'Error'. The names of the segments in the 7-segment display, and the glow of the display for '0', '2', '5' and 'E', are shown below.

Consider
1. push button pressed/not pressed is equivalent to logic 1/ 0 respectively
2. a segment a to g are considered as functions of P1 and P2, then which of the respectively.
If segments a to g are considered as functions of P1 and P2, then which of the following is correct?
g = P1 + P2, d = c + e
g = P1 + P2, d = c + e
g = P1 + P2, e = b + c
g = P1 + P2, e = b + c
Explanation:

From the figure

49.
Laplace transform of {t cos at} is:
Explanation:

x(t) x(s)

.

50.
The following series RLC circuit with zero initial conditions is excited by a unit impulse function δ(t).

For t > 0, the output voltage Vc (t) is