Physic-2000-Set-II

Q1) Draw an equipotential surface for a point charge Q > 0.
(Marks 1)

Ans1) Equipotential surface are the surface of concentric spheres with the charge at their centre.

Q2) If the ratio of the horizontal component of earth’s magnetic field to the resultant magnetic field at a place is 1/2, what is the angle of dip at that place ? (Marks 1)
Ans2) Cos = BH/B = 1/2
= 45o

Q3) How does the energy gap in an intrinsic semiconductor vary, when doped with a pentavalent impurity ? (Marks 1)
Ans3) Decreases

Q5) Why is the transmission of signals using ground waves, restricted only to a frequency of 1500 kHz ? (Marks 1)
Ans5) The transmission of signals using ground waves is restricted only to a frequency of 1500 kHz because it becomes weaker as the frequency increases as they are damped by interaction with matter.

Q9) Four capacitors are connected as shown in the figure given below :

Calculate the equivalent capacitance between the points X and Y. (Marks 2)
Ans9)

The equivalent circuit is

C1, C2, C3 are in parallel. There equivalent capacitance = C’ =C1 + C2 + C3 = 20 + 30 + 50 = 100 F
This equivalent capacitance is in series with C4.
Net capacitance ‘C’ is given by
1/C = 1/C’ + 1/C4 = 1/100 + 1/100 = 1/50
or C = 50 F

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