# Physics-2000-Set-III

**(Only those questions have been answered, which are different from Set I and Set II)**

**Q6) Name the electromagnetic radiation which has the largest penetrating power. (Marks 1)**

Ans6) Gamma rays have the largest penetrating power.

**Q7) Two planets A and B have solar constants 50 W/m2 and 1400 W/m2 respectively. Which one of the two planets has a higher temperature ? (Marks 1)**

Ans7) Solar constant is proportional to fourth power of absolute temperature. Solar constant of B is greater than that of A. So temperature of B is higher than that of A

**Q8) What is the polarising angle of a medium in which the angle of refraction is 33o? (Marks 1)**

Ans8) Angle of refraction (r) = 90o ip where ip is polarising angle

ip = 90 – r = 90 – 33 = 57o

**Q10) Briefly explain how the distance of a superior planet can be determined from earth. (Marks 2)**

Ans10) The distance of a superior planet can be determined from earth by applying kepler’s third law of planetary motion. According to this law

T2 R3

Where T is the time period of revolution & R is the semi-major axis of the orbital path of planet around the sun.

Let T1 & T2 be the time period of revolution of earth and the superior planet R1 & R2 be their respective semi major axes. Then

T12/T22 = R13/R23

or R2 = R1 (T2/T1)2/3

Knowing R1, T1 & T2 the value of R2 can be calculate.

**Q13) Four capacitors are connected as shown in the figure given below :**

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

Ans13) The equivalent circuit is

C1, C2, C3 are in parallel. There equivalent capacitance = C’ =C1 + C2 + C3 = 5 + 10 + 15 = 30 F

C’ is in series with C4.

Their equivalent capacitance C is given by

1/C = 1/C’ + 1/C4 = 1/30 + 1/30 = 1/15

or C = 15 F