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Monthly Archives: December 2010

Buzzing sound from a transformer – Magnetostriction

Subasaraswathi asks:

Why does a buzzing sound come from an electric transformer?

In which direction should we lie to sleep?

Haritha asked:

it is heard that we should not lie in north-south direction.is there any explanation for it?


Answer to be posted soon.

BMMD – Body Mass Measuring Device

Priyanka asked

What is a BMMD? How does it work?


BMMD stands for Body Mass Measuring Device used by astronauts, which is basically a spring mounted chair which measures mass as a measure of inertia. As you know, one experiences weightlessness inside a satellite and normal methods of measuring mass do not work. (like a common balance or a spring balance). The time period of oscillations which depends on the force constant and mass is used in measuring mass in BMMD used by an astronomer

Determinism, quantum theory and …. ?

Anchu Wilson asked:

It is known that the behaviour of microscopic particles and systems cannot be predicted.Like, the exact position of an electron cannot be determined ,but that we can give only a probable region where this can be found.So can this theory be applied to support (at least theoretically)the existence of parallel universes,where the lack of determinism in Quantum Theory can be applied ? Suppose in one universe something happens,the reverse happens in a parallel universe,just like the position of electron is indeterminate?

Can the theory of existence of parallel universes be refuted or proved?



Such a question I have discussed elsewhere in the site already. The theory of parallel universes or multiple universes is one which comes into discussion when quantum mechanics and the theory of probability is discussed.

Schrödinger’s cat is a relevant thought experiment which can be considered in this discussion.

Imagine a cat inside a box. The box is provided with a mechanism which triggers a system which inject potassium cyanide to the cat. The box is also provided with a single atom of a radio active substance. The life period of a single atom of a radio active element varies from 0 to infinity. SO, the atom may or may or decay in a given time interval. If the atom decays, the radiation emitted will trigger the cyanide injection system and it will instantly kill the cat.

If the cat is inside the box and the box is kept closed for one hour, What is the state of the cat?

Is it dead or alive?

When after one hour we open the box and see, we will EITHER  see a DEAD  cat or a LIVE cat depending on whether the atom decayed or not.

But the probability of decaying or not decaying of the atom during the one hour are equal. Then when we are not looking at the cat, what can we say about the state of the cat?

We can say that it is the superposition of the two probabilities. But when we make an observation, only one of the probabilities become a reality.

What happens to the other probabilities?

Some say that there is a MASTER MIND which determines which of the two (or many) probabilities should become the reality. One of the many probability becomes a reality and all others collapse.

It’s right to remember one saying in this context;

“To say YES to somebody is to say NO to all others”

The another theory explaining the probability turning to reality is that, whenever we make an observation, or take a result, the universe splits into as many as the number of probabilities.

So, it’s not a Universe, but a MULTIverse.

We don’t know what actually is taking place. But it’s very thought provoking to read and think on such ideas and theories.

Here are some links which you can use for further reference.

Short circuiting, overloading, Area vector

Gopika asked:

What is the basic difference between short circuiting & overloading?
Why is area considered as both scalar and vector quantity?



Short circuiting

As such the words suggest, the circuit becomes shorter. If there is a failure in insulation or some other means by which the two wires (phase and neutral) comes into electrical contact, the circuit gets shortened as the current always chooses the path which has got least resistance. Since the resistance of the shorted circuit is less a heavy current flows.


In house hold circuiting we are using parallel combination of the different appliances. Every instrument is connected in parallel to the supply. Whenever a new apparatus is switched on, it draws more current. If the current drawn by all the devices connected in a circuit is more than the maximum current rating for the given circuit, the condition is called overloading.

Fluorescent lamp flickers and incandescent lamp does not!

Swathi asked:

Why do fluorescent lights flicker (tube lights) while Incandescent bulbs don’t , especially when they are switched on..Is it an effect of the pulses as sensed by the retina?


If your question is regarding the start up flickering,

the fluorescent lamp requires a very high voltage to start conducting. In a lit up tube light, the conduction is taking place through the gas filled inside the tube. As you know, air is a bad conductor. To make it conducting, it is to be ionized first. This is done by developing a very high potential difference between the two ends of the tube by the combined action of starter and the choke. Starter is a make and break arrangement which makes the supply intermittent. When the supply is disturbed, a huge potential difference is developed and flashes produced inside the tube ionizes the gas inside the tube. After such a few occurrences, the gas will be ionized enough to make the gas conducting. During this process lot of UV radiations are emitted. This strikes the fluorescent coating on the tube which converts UV radiations to visible light. So, the tube light flickers due to the action of starter during the startup time.

But, if your question is with regard to the flickering of a lit up fluorescent lamp, …………. 

I will answer it later

Black Holes and Thermal Radiation

Varun G asked

“Do black holes produce thermal radiation, as expected on theoretical grounds and do they absorb light?”

Ans: Hope you are talking about the Hawking radiation.

Any body at a temperature above absolute zero emits radiations. If the temperature of black body is not absolute zero (It was Stephen Hawking who predicted that black holes should have a finite, non-zero temperature, and hence the name “Hawking Radiation”) it will emit radiation.

In a black hole emitting radiation, there is a loss of mass. If the mass decreased due to Hawking Radiation is more than the mass gained by the black holes via alternate means, the net mass of the black holes will go on decreasing. (This is called “black hole evaporation” Further, it has been noted that the black holes with lower mass emit more radiations than the heavier ones.

This answer may seem contradicting the definition of black hole itself.

“A black hole is a body whose gravitational force of attraction is so huge that even electromagnetic radiation cannot escape from it” as the definition goes.

But the Hawking Radiation is caused by Quantum effects. The processes behind the “escape” of radiation from a black hole is thought to be

  • Vacuum Fluctuations and
  • Quantum tunneling

The above terms and concept will be too high to be discussed at school level. However for the curious ones, I am giving some links to explore.

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