## How to get pass marks in Physics in days?

Some students asked me this. These were students who never passed in any of the Physics tests during the year when they were in class 12.

Now that the exams are near, they are eager to pass with least effort.

I consoled them, and said, “If you believe and promise to do what I say, you can get more than pass marks in just  days effort.”

They agreed.

The formula I gave them and which fetched them good marks is listed below.

1. There are some derivations and constructions which are commonly asked in exams. With the help of your teacher identify the portions and learn them well. Take atleast fifteen such portions. Write and practice. Remember, these five days can change your future for ever.
2. Write all formulae with explanation of each term in a paper. Use them to solve atleast five numericals from each chapter.
3. Write all laws and principles and learn them by heart.  Try to write from memory and make sure that you can do it without any mistake.
4. Practice all diagrams
5. Revise whatever you learnt

Here you go! Do the above with confidence. Practice well, avoid distractions. Eat healthy food. Pray and practice. YOU WILL WIN

## Questions asked in Physics Viva Voce for Class 12 Physics Practical

Q1. Why are the resistances used in a resistance box is like 1,2,2,5,10,20,20,50,100,200,200,500,1000,2000,2000,5000 etc?

Ans: In this arrangement all natural numbers upto 10000 ohms (and above) can be realized.

1, 2, 2+1=3,2+2=4,5,5+1=6,5+2=7,5+2+1=8,5+2+2=9 etc

Try it yourself to get all numbers from 1 to 10000

Q2. Why wire is double folded in resistance box?

Ans: The resistance wires in resistance box and in standard resistances are double folded and then coiled so as to nullify the effect inductance. When double folded and coiled, in one half the current will be clockwise and in next half the current will be anticlockwise. Therefore, the magnetic induction created by one half will be cancelled by the other half.

Q3. we make coil of wire when finding resistance of wire through metre bridge ?

Ans: This is not correct. If it is to be coiled, it should be done as in Q1.

Normally the wire is stretched on a half meter scale and fixed with terminals (or arranged in some other manner)

If you feel that the wire need to be coiled, then take  care to avoid the magnetic effect.

## Found on the net – Physics Catalyst

We browse the internet to find out useful website for the learners. One such website we found today

http://physicscatalyst.com/chapter.php

## How was your AISSCE CBSE Class 12 Physics Exam 2013?

How was the CBSE Class 12 Physics Exam today?

Was it easy or difficult?

Many students reported that the questions were unexpected and extra ordinarily tough. What was your experience?

Were there questions beyond your comprehension?

Were there questions out of Syllabus?

Anju R  writes:

Hi,
The Physics CBSE exam was tough.It was not beyond the syllabus but it was confusing and was asked in a twisted manner.Almost all the students who prepared for the exams didnot leave any derivations,laws etc.But the saddest part was that they asked the big derivation for just one mark and only very few were asked.And most questions were unexpected ones.
It was painful when I saw that after the exam almost all the students were crying.Sitting for a whole night for studying the derivations,laws etc.. gave nothing to us other than tears.We were happy after the English exam but the Physics exam gave a terror over us about Board Exams.I think 90 %  of the students could not complete saying that it was a lengthy paper.

During the exam I could see many sitting with great confusion while few others in a hurry to complete  it and the rest of them sitting sadly.By the grace of God I completed 5 minutes before the alloted time and didn’t leave any question.I hope CBSE will consider us.

Yours sincerely,
Anju.R

## Faster than Light!

Mathew Abraham (A Physics Teacher in KVS) claims (on FaceBook) that faster than light communication and transfer of matter is possible and the fact will be revealed in near future.

See the transcript below.

I believe and maintain that “faster than light communication and transfer of matter is possible”. We have to find how?

• Vishnu V Mohan Maybe communication.But wat abt matter?
• Mathew Abraham It’s somewhat like a revelation to me, I hope that particles travelling faster than light would soon be discovered and that discovery would lead to interstellar travel in near future

## Physics Musings on Beer

Do you know there are a lot of Physics facts hidden behind a glass of beer.

Institute of Physics (UK) has launched a Christmas website based on beer, to help explain some of the more peculiar scientific phenomena hidden in a glass of beer.

http://www.physics.org/cheersphysics/

The site explains many facts of Physics too based on the beer story.

It says that the bubbles are not rising but they are constantly falling in a g;ass of beer. Can’t believe? Visit the site to know more.

## Question Bank in Physics Class XII

The collection will also be helpful for students of other syllabuses.

The file consists of syllabus, key points, collection of very short Answer (1 mark), Short answer type question – solved (2 marks), short answers (3 marks), Long answers (5 marks), Solved numericals and 3 sample papers.

The contents are arranged chapter-wise. Any student will find this a boon for easy preparation and to score better marks in Physics.

## Alternating Current and Direct Current

AC/DC (electricity)

Electricity is the most widely used form on energy because it is most efficiently distributed and transported. Also it can be easily converted to other forms of energy like mechanical energy, heat energy etc. Also since it is one of the fastest forms of usable energy it is used in logic digital circuits for computation since it gives the fastest results. It is this versatility of electricity that makes it so useful for modern life.
Of course electrical energy has various forms as well. It can be stored charge, alternating current or direct current. Each of these forms of energy have different advantages. Now we know that most  of power that we get in our homes is in the form of AC. However it is not necessarily the most used form of energy. In fact most electronic equipment use DC power and converts AC from the supply to DC. Then why is it made AC in the first place. Let us discuss that shall we?

Continue reading “Alternating Current and Direct Current”

## Inside a Car Engine

(Internal Combustion Engine)

We cannot imagine modern life without the car. The automobile has been one of the singular most amazing inventions of the 21st century and almost defines modern times. Inside of most mechanical petroleum based vehicles is the internal combustion engine.
Today we shall have a brief look at the internal combustion engine and it’s basic working principles.
Basically the the internal combustion engine is a cyclic machine that works on the basis of polytropic expansion laws.
polywhat?!

Ok so a polytropic process is one in which the gas equations work differently than that stated in boyle’s law because temperatures need to be constant for the famous law to work. (Pressure*Volume= constant at constant temperature)
Here since during expansion of the gases the temperature does not remain constant and hence the law looks like:
Pressure*Volumex =constant

The variable x depends upon the gas used.

So as you can see pressure will have to change greatly for the equivalent volume to change and to keep the equation valid. That’s exactly what happens in an internal combustion engine where an small explosion changes the pressure greatly but the limited volume is not much and hence the equivalent change in volume remains small.

First cycle: Suction
As you can see from the diagram the camshaft being slightly oval is rotating about a central point which for a certain time pushes the lever which opens the valve connecting the gasoline tank to the combustion chamber. The engine is so tuned such that when the fuel flows from the gasoline tank to the combustion chamber the bigger rotating structure downwards pulls the piston downwards. Hence the fuel gets trapped in the chamber when the valve closes.

Second cycle:Compression
This is the part where things get interesting. With the fuel trapped inside the chamber due to valve action the wheel rotates such that it pushes the piston above and compresses the fuel. This fuel now now has to withstand high pressure as the piston has lowered the volume greatly. When it is compressed at the maximum a spark plus in the chamber is ignited which causes a small explosion to increase pressure rapidly and push the piston downwards.[remember the part where i told you that the volume is quite limited but the change in pressure is enormous]

Third cycle: Expansion
Here work is obtained from the engine as it causes the rotation in the rotating part attached to the piston to increase. The expansion is the part where the actual energy is obtained from the engine. The wheel continues to rotate by inertia. This is why sometime you need to move the car a bit before getting it to work. It is because the first two parts of the cycle need energy to function and it’s the third cycle which actually provides work.

Fourth cycle: Exhaust
Now the second camshaft is made to rotate at such a speed that by the end of the third cycle  the exhaust valve opens up and the fumes that remain after the explosion is forced out by the upward movement of the piston.
Now the second cycle starts where the piston is made to move by inertia and hence the cycle continues.

That’s it! That’s how the internal combustion engine works. Now obviously you will not get an exact replica of this engine inside your car. Rather they have as many as four piston moving up and down to form a 4-stroke internal combustion engine. Also they have a variety of cooling mechanisms and noise filters to reduce the noise from the explosion that takes place inside the machine. However this is the absolute basic and all other made upon this model. There are differences between a petrol and a diesel engine but then again they are not much different from this model.
So now the looking up the car engine  won’t seem like an engineering job at NASA anymore, would it?!