## Sunday, October 28, 2007

### H C Verma JEE Physics Ch. 11 GRAVITATION

A newly discovered planet is 13.5 times more massive than the earth but half as dense. Approximately, how much longer would it take to orbit this new planet, and why is your answer an approximation?

Solution:

Since density is mass/volume, the only way that the planet is 13.5 times more massive and yet half as dense is if it has 27 X the volume. If the planet is 27X more voluminous, and since it is probably spherical like the earth, it will have a radius that is three times(cube root of 27 = 3) larger.(the rest of terms cancel in the volume of sphere formula.) The circumference will also be three times larger, and at equal speeds, it will take approximately three times longer to orbit. The reason it is an approximation is that in reality you have to factor in the height above the surface. Let it equal to h, and let R = radius of earth. Cp= circumference of orbit around new planet;
Ce= circumference of orbit around Earth;
the ratio of the circumherences then becomes
Cp/Ce = 2p(3R +h)/[2p(R +h)]
If h is a lot smaller than R, then the answer will be approximately 3.

Source:
http://www.emsb.qc.ca/laurenhill/science/07scsoln.html
april 07 solution

### JEE Physics Ch. 23 HEAT AND TEMPERATURE Questions

If equal and separate masses of alcohol and water are initially at the same temperature and they are heated for a short while, the alcohol will experience a higher change in temperature. What inverse relationship accounts for this behaviour? Why do we specify for a "short while"?

Solution:

Since water has a higher boiling point, it will eventually experience a higher change in temperature, but initially, prior to boiling, alcohol heats up faster, even though it absorbs the same amount of heat as water. This is a result of alcohol's lower specific heat.

Source:
http://www.emsb.qc.ca/laurenhill/science/07scsoln.html
May 07 question

### Questions Ch 36 Permanent Magnets

Problem from a set published in Eenadu on 29.3.2008

Two small magnets of moments 0.108 Am² and 0.192 Am² are placed on the two mutually perpendicular lines. The distance between the points of intersection of these lines respectively 30 cm and 40 cm from these magnets. The resultant field at the point of intersection is

a) 1*10^-6 T
b) 2*10^-6 T
c) 3*10^-6 T
d) 4*10^-6 T

procedure

### Questions Ch. 44 X-Rays

Simple Questions

1. What are X-Rays?
2. What is a Coolidge tube?
3. What is the difference between Cathode Ray tube and Coolidge tube?
4. distinguish between characteristic X rays and Continuous X rays.
5. Differentiate between K X rays and L X rays.
6. What is Moseley's law?
7. What is Bragg's law?

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Give Reasons

1. X rays are not deflected by electric or magnetic field.
2.

### Simple Questions Ch. 46 The Nucleus

1. What are the masses of proton and neutron?
2. What are the masses of proton and neutron in enegy units?
3. What is a unified atomic mass unit?
4. What chacteristics of atoms are represented by symbols A, N, and Z?
5. what are isotopes, isotones, isobars and nuclides?
6. How many nuclides are identified by physicists?
7. What is highest N/Z ratio identified?
8. what are radio active nuclides?
9. What is the formula for average radius of a nucleus?
10. what is formula for average volume of a nucleus?
11. What is nuclear spin of nucleus?
12. What are nuclear forces?
13. What is relation between nuclear force and charge?
14. What is binding energy?
15. what is mass excess?
16. what is Alpha decay?
17. What is beta decay?
18. disinguish between beta minus decay and beta plus decay?
19. what is gamma decay?
20. What is Q value of a process?
21. Distinguish between neutrino and antineutrino.
22. What is antiparticle of an electron?
23. What are characteristics are measured by units Bq and Ci?
24. Define activity of a radioactive material.
25. Left to itself, the heavy nucleus will not break according to classical physics. Is the statement true?
26. What barrier penetration?
27. What is Heisenberg uncertainty in the context of nuclear fission?
28. What are the constituents of natural uranium?
29. How do you prepare [236,92] uranium from natural uranium?
30. Give two combinations of fragments formed due to fission of [236,92) uranium.
31. what is a breeder reactor?
32. what is temperature inside the sun?
33. what is Tokamak design?
34. what is inertial confinement?

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II. Give reasons for the following.

1. According to calculation by physicists, a temperature of the order of 10^9 K is required if deutrons are to be fused. But the temperature inside the sun is estimated to be around 1.5*10^7 K and the fusion is going on.