PHYSICS MUSING MUSING
SOLUTION OF JULY 2016 CROSSWORD
Winner (July 2016)
• Swastik Biswas, Kolkata
Solution Senders (June 2016)
• Devjit Acharjee, Kolkata
It is very interesting to solve the crossword of Physics For You.
It enhances knowledge in Physics, and being a science lover I enjoy it very much. So, thanks for the thought of the crossword.
• S. Sharanya Bharghavi, Mumbai
Solution Senders of Physics Musing Set-36
1. Virat Vyas, Bhopal (M.P.) 2. Suman Mondal, Kolkata (W.B.) 3. Rupesh Singh, Gorakhpur (U.P.)
Q1. What is the origin of 4pe0 in the formula of electrostatic force and µ
p0
4 for magnetism?
–Ms. Aarohi Pandey, Mandsaur (M.P) Ans. The original formula given by Coulomb, for the
force between two point charges is F kq q
=± r1 22 , +ve for repulsion and –ve for attraction.
The force is proportional to the product of the charges and inversely proportional to the square of the distance between them.
q+1
Later, when Gauss gave his theorem,
∫
E dS q ⋅ =e1+0 where q1+is the charge enclosed.But dS
∫
= 4p for a sphere, the gaussian surface r2 for point charges as well as spheres.E q
For magnetic field also one gets µ p0
Here it makes no difference.
But k was put 1
4pe and the similar constant for 0 magnetism as µ
p0
4 to suit the S.I. units. Once the units are settled, the k was changed.
But this was a great choice, suggested by Gauss the controversial to the trivial, the team will tackle the questions, easy and tough.
The best questions and their solutions will be printed in this column each month.
Y U ASK
WE ANSWER
other values of areas were adjusted so that 1 4pe0 was kept intact.
Any good formula should lead to other discoveries and fit into the mosaic patterns in various fields.
4pe0 4µ0 0 0 p e µ
⋅ = = a constant whose value was the same as 12
c , being the velocity of light. c This gave the clue to Maxwell to identify light as an electromagnetic wave. The connection between light and electromagnetism was seen by him.
This was a great step in the theory of light.
Many gems of truth are scattered everywhere. The great scientists recognize the truth behind the scattered formulas.
Q2. Entropy of the universe is constantly increasing – Can this be applied at atomic levels and other topics in modern physics?
–Ms. Poonam Madhe, Nasik (Maharashtra) Ans. According to White O.M. (Heat), entropy is a
mathematical concept. The change in entropy is Q
T where Q is the quantity of heat taken in by the body at temperature T.
From Carnot cycle’s discussion, for a particular
Entropy increases in all irreversible changes.
Perfectly reversible cycle is only theoretical. There are always leakages of heat and the insulators are never perfect. Therefore every time a machine works, the sink gets hot. In normal engines, entropy increases.
The second law of thermodynamics as stated by Clausius is that the entropy of the world tends to a maximum. We should not mix modern physics with classical physics, although later you may find their applications.
Q3. Why do doors and windows find it difficult to get closed in cold weather?
–Mr. Arun S Ans. In cold weather due to increase in humidity in the
atomosphere water does not evaporate rapidly.
So, the cellulose in the wood expands due to the added water content and swells hence it does not
fit the door frame.
SmalleSt microwave detector created
Researchers have created the world’s smallest and most sensitive microwave detector, beating the previous record by fourteen fold, an advance which may help in making ultra-sensitive cameras and accessories for emerging quantum computers.
The detector, which is smaller than a human blood cell, has a simple design of superconducting aluminum and a single golden nanowire. “For us size matters. The smaller the better. With smaller detectors, we get more signal and cheaper price in mass production,“ said Mikko Mottonen from Aalto University in Finland.
This design guarantees both efficient absorption of incoming photons and very sensitive readout. The whole detector is smaller than a single human blood cell, the researchers said. The new detector works at a hundredth of a degree above absolute zero temperature.
volcanoeS go quiet before they erupt
Periods of seismic quiet occur immediately before volcanic eruptions and can thus be used to forecast an impending eruption for restless volcanoes, scientists say.
When dormant volcanoes are about to erupt, they show some predictive characteristics - seismic activity beneath the volcano starts to increase, gas escapes through the vent, or the surrounding ground starts to deform.
However, until now, there has not been a way to forecast eruptions of more restless volcanoes because of the constant seismic activity and gas and steam emissions. Diana Roman, a volcanologist at Carnegie Institution for Science (CIS) in the US, working with a team of scientists from Pennsylvania State University, Oxford University, the University of Iceland found that periods of seismic quiet occur immediately before eruptions and can thus be used to forecast an impending eruption for restless volcanoes.
The duration of the silence can indicate the level of energy that will be released when eruption occurs.
Longer quiet periods mean a bigger bang. The team monitored a sequence of eruptions at the Telica Volcano in Nicaragua in 2011. It is a so-called stratovolcano, with a classic-looking cone built up by many layers of lava and ash.
They started monitoring Telica in 2009 with various instruments and by 2011 they had a comprehensive network within four kilometres of the volcano’s summit.
Stephen Hawking, one of the world’s best-known physicists, is set to announce plans to map the entire known universe using a supercomputing centre he founded at Cambridge University.
The Cosmos computer will plot the position and movement of billions of galaxies, black holes, supernovas and other cosmic structures, ‘The Sunday Times’ reported.
Hawking, the author of ‘A Brief History of Time’, will detail the plans of this super map during a talk to some of the world’s most eminent scientists at the Starmus science conference, which begins on June 27, 2016 in Tenerife, Spain.
Paul Shellard, Cambridge University’s professor of cosmology and director of the Cosmos computer centre, said it would use images of radiation from the Big Bang captured by the European Space Agency’s Planck satellite to draw up a map of the early universe.
“Planck gives us an amazing picture of the early distribution of matter and how that led to the structure of the modern universe,” he said.
The images will be augmented by data from the Dark Energy Survey, which has a 13-feet diametre telescope in Chile, to map hundreds of millions of galaxies and reveal the nature of the dark energy that is accelerating the expansion of the universe.
hawking to announce planS to map univerSe
solution set-36 1. (b) : Charge on inner shell,
qr = –s(4pr2)
Charge on outer shell, qR = s(4pR2) Potential of given system of shells for different values of x,
(i) 0 < x ≤ r, V q
3. (a) : According to question, frequency of torsional oscillation = frequency of vertical oscillation,
1
BQ is because of two currents in same direction.
BR is because of two currents in opposite direction.
5. (d) : By symmetry, magnetic field cannot exist.
6. t=mgR q= −I d q sin dt22 For small amplitude, sinq ≈ q
\ ddt
Total heat generated =Q J
C
So, required heat generated = 5 8
1 10
1
× =16J 8. On first touch of electrometer with metal ball
Vmetal = Velectrometer
⇒ q1C1 = (Q0 – q1)C2 Net charge transfer, q Q
C
Similarly after second touch,
q q n more times to get electrometer voltage equal to 1 kV.
Hence, electrometer reads less than 1 kV for n = 6.
9. Using Newton's second law of motion, f = ma
Taking torque about centre of mass, t0 = Ia FR fR mR a
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ACROSS
2. A cathode from which electrons are emitted as a result of the photoelectric effect. [12]
6. The stationary electromagnetic structure of an electric motor or generator. [6]
7. A group of magnesium alloys used to enease uranium fuel elements. [6]
8. Commonly used to improve the frequency response of a loudspeaker. [6]
11. The reciprocal of dynamic viscosity. [8]
14. A dimensionless number used in problems involving both heat and mass transfer. [5, 6]
17. Any of a class of heat-resistant materials made of ceramic and sintered metal. [6]
21. A system of axes that forms a frame of reference. [9]
23. The derived SI unit of activity equal to one disintegration per second. [9]
24. A self-evident proposition not requiring demonstration. [5]
26. A type of astronomical object with a mass between that of a large planet and a small star. [5, 5]
27. A transuranic radioactive chemical element with symbol Cm. [6]
28. The branch of physics deals with deformation and flow of matter. [8]
29. A negatively charged elementary particle classed as a lapton. [5]
30. An instrument for measuring the changes in magnetic flux. [9]
DOWN
1. An elementary particle, charged or neutral, classified as a hyperon. [5, 8]
2. It is equal to one joule second. [6]
3. A high-pitched audio frequency tone heard in receivers. [4]
4. A temporary connection between electronic circuits. [6]
5. A pair of closely spaced lines in a spectrum. [7]
9. A unit of frequency. [7]
10. An abnormal transient electrical disturbance in a conductor. [5]
12. An apparatus for studying thermal expansion. [11]
13. A formula for calculating moments of inertia. [4, 4]
15. A type of switch that operates using superconductivity.
[8]
16. An alloy of lead and tin. [6]
18. The property of allowing the passage of lines of magnetic flux. [9]
19. The process by which a solid undergoes plastic deformation. [5]
20. Denotes a nuclear process that absorbs energy. [9]
22. A powdery metallic oxide formed when an ore has been heated. [4]
25. A unit for measuring signal speed in a computer. [4]