Posted: October 21, 2014 in Uncategorized


It’s been more than a week into the vacation. I suspect there must be an expectation at home now that you spend some time with your academic work. So unless your family is busy looking forward to Diwali, I guess it’s the right time for me to pop up and ask you to do some physics.

I am sorry I couldn’t finish the correction of papers in time. You all generally have done well. We will discuss the paper in detail once you are back here. I also want to clarify here that the mark sheet which you will receive (in a few days) will have your theory (80) plus your lab work (20) marks combined for physics.

I would like you all to begin by revising Optics and Electromagnetism (for 10 B students). Read your textbook thoroughly.

For the coming term, I would like you all to read through the chapter on Sound and Modern Physics. Class 10 B students should also read through the first two chapters of Mechanics from the textbook.

I will also post some worksheets or may be test papers for revision work.

Sorry!!! No homework.

Posted: April 14, 2014 in Uncategorized

I am sorry but it doesn’t look like I’ll be able to maintain this blog this vacation due to my travel plans and internet accessibility issues.

In case you have any specific individual queries, you can drop in your question as a comment to this post and I’ll be able to respond to those. You can of course browse through the older posts on this blog. There is more than enough interesting material to look at.

Do please revise the portion that is relevant for your coming academic year.

I was busy here with lots of end-term work and will be leaving with class 10 students for their excursion to SPS tomorrow. So the blog will become active only after my return on April 12th. Enjoy your vacations!

Questions and Answers

Posted: November 12, 2013 in Uncategorized

Sorry for taking this long to respond to your questions:

Qn 1. About the production of electricity using different sources of energy and what is required for the exam.

You need to know the energy transformations taking place in each case but you should not be asked any details about the process (diagrams, etc.) in the exam.

Qn 2. About gears in simple machines.

I’m going to teach about gears in the class. And about non-ideal (efficiency < 100%) pulley systems.

Qn 3. About resistivity of an electrolyte.

Resistivity of any material (solid metal or liquid electrolyte or a gas) is defined as the electrical resistance of the material of unit length and unit cross-sectional area.

For example, resistivity of NaCl solution is the resistance that this solution will offer between two electrodes which are 1 m apart and have an area of 1 m2.

Resistivity of an electrolyte does depend on the nature of the electrolyte, on the concentration of ions in the electrolyte and of course, on the temperature.

Qn 4. About high-tension wires.

High-tension wires are wires especially constructed to carry electric currents at very high voltage. So they are used in high-voltage applications, e.g. in heavy industries or in high-energy physics research labs.

Qn 5. About solenoids and coils and qn. 3 (d) from the term-end exam paper.

A coil is not a solenoid. A solenoid is not a coil.

Both are several turns of a wire wound generally over a cylindrical base.

The difference lies in the shape. A coil looks like a loop of thread while a solenoid looks like a spring. A coil is flatter, a solenoid is longer.

Technically, a coil has a diameter larger than its thickness while a solenoid has a thickness (or length) larger than its diameter.

Qn 6. About two-way switches and the double-pole switches.

They are different. A double-pole switch is like two switches mechanically joined together. So using a double-pole switch you can disconnect (or connect) a pair of wires with another pair of wires. An example is the kind that is used as Main Switch in the household circuits to connect (or disconnect) both Live and Neutral wires inside the house with the Live and Neutral wires coming from outside, by a single throw (flip).

A two-way switch is used to connect a wire to any one of a pair of wires. See the kind that is used in staircase switching. Or the one Edison used in his exploration of the thermionic emission from carbon filaments.

Qn 7. About high-tension, low-tension batteries.

I don’t know the story behind it but tension in electricity refers to voltage. So, a high-tension battery is a battery which can provide high emf (potential difference between its electrodes or terminals). The batteries we usually use are 1.5 V to 12 V batteries and these are called low-tension batteries. For a gas to become conducting, it has to be kept at a very low pressure and a very high voltage has to be applied across it. Therefore for thermionic emission in gases, they had to use high-tension batteries.

Qn 8. About the acceleration of the beam by anodes in cathode ray tube.

Anodes are +ve plates in cathode ray tubes. So negatively charged beam (which comprises of electrons) experiences a force towards the anodes and gets accelerated.

Qn 9. About radiations and waves.
Radiations is a loose term associated both with electromagnetic waves and with the particles emitted from radioactive sources. So, alpha, beta and gamma emissions from radioactive nuclei were also called radiations though out of these only gamma emissions are waves. So gamma radiations can be said to have wavelength (in a classical sense) while alpha and beta emissions are streams of particles.

Qn 10. About using lead for protection against radioactive radiations.

Any heavy metal (go far down in the periodic table) is good at absorbing radioactive emissions. Lead is probably the cheapest of them all. That could be the reason why it is so extensively used in safety gear in radioactive establishments.

Qn 11. About deflecting system in cathode ray tube being like a box.

Yes, the X- and Y-plates can be imagined as two pairs of opposite sides in a box.

Qn 12. About thermometer project.

Use ANY design! It should be working, that’s all. DON’T USE MERCURY THOUGH!

Qn 13. About the centre of gravity of a cone. “The centre of gravity of a solid cone lies at a height 1/4 from the base on the axis whereas the centre of gravity of a hollow cone at a height 1/3 from the base. What’s the difference based on?”

A solid cone is “more biased” towards its base in terms of its mass than a hollow cone is. So for a solid cone, the CG gets “pushed down” further towards the base. Does that make sense? Or are you looking for a more rigorous proof/argument?

Qn 14. About drag being a contact force.

It is a contact force. It is not exactly like friction between two solid surfaces. It is a due to what physicists call ‘viscosity’ of fluids, which you can say is a kind of friction or drag force between different layers of a moving fluid. Drag force is different from friction in many ways, one of them being that it is dependent on the relative velocity between different layers while force due to (kinetic/sliding) friction is independent of speed.

Qn 15. About Schrӧdinger’s cat experiment.

Schrӧdinger’s cat experiment is a thought experiment suggested by physicist Erwin Schrӧdinger. It is built around a certain interpretation of quantum physics (called Copenhagen interpretation). You can look at these links to know about it further:The Physics behind Scrӧdinger’s cat Paradox and Wikipedia, of course!

schrodinger-catCredit: http://chaospet.com/comics/2007-09-01-33.png

‘Space Ferrari’ falls to Earth

Posted: November 11, 2013 in Uncategorized

Read this story from BBC here: European Space Agency’s Goce satellite falls to Earth

Project: Make a thermometer

Posted: November 9, 2013 in Uncategorized

Some of you had made a working model of an electric motor or that of an electric generator during your summer vacation. I suggest that others make a working thermometer. Of course, if you have made a motor/generator and want to make a thermometer too, do it. It should be fun.

A thermometer measures temperature of an object. It is difficult to make an instrument which directly measures temperature. Often thermometers measure some property of the object which changes with its temperature. And then you calibrate this changing property with the actual temperature of the object (using another thermometer) and you have your thermometer ready.

So you will have to look for some physical property that changes with temperature and that you can easily measure. Examples of physical properties that change with temperature are size (length, area, volume), resistance, refractive index, etc.

It might be a good idea to look for different kinds of thermometers on the Internet and then decide which kind you would like to make for yourself.

Once you are ready with your thermometer, prepare a sheet for your design with the following details:

Diagram of the design:

Materials used: [What were the materials that you used to make your thermometer?]

Approximate cost of construction: [How much does your thermometer cost? In terms of raw materials. Let's leave out the costing of manual labour and ingenuity, etc.]

Physical property that the thermometer actually measures:

Kind of objects that the thermometer can measure the temperature of: [All thermometers are designed to measure the temperature of specific kind of things, e.g. liquids, human body, furnaces, air, etc.]

Range: Minimum and maximum temperatures that your thermometer can measure.

Accuracy: [Check your thermometer with another thermometer and see what the difference is. When you check the temperature of different objects you may find that your thermometer differs from the other thermometer by 2 to 7 degree Celsius. Then the accuracy of your thermometer is +/- 7 degree Celsius.

Resolution (or Least Count): [What is the smallest temperature difference your thermometer can measure? 5 degrees, 2 degrees, 1 degree, 0.5 degree? That's the resolution.]


I had asked you to watch a lecture from MIT OCW on the discovery of electron and nucleus. See here: http://physicsfor10.wordpress.com/2013/11/05/preparation-for-modern-physics/

Here’s a small quiz I’ve prepared which you should take after you’ve watched the video: http://tinyurl.com/l6r6bm7

I’m not sure about this but you may have to use your Google account to take the test.

ps: In the next post, I will respond to the questions that some of you’ve asked.