CBSE

How was your Physics Practical Examination?

Hello students!

It’s the time of AISSCE Practical Examination.

How was your Physics Practical Examination and Viva?

Which questions were asked to you?

Which were the experiments and activities you were asked to perform?

How farely did you do it?

Share your experience here as comments to this post. Your responses will be a boon for the others.

You can post the questions you were asked during Viva so that others can find the answers to them and learn for the Viva during their turn.

Class 12 Physics : Electrostatics Revision Test

Max marks:50 Time:2hrs

1. A glass rod rubbed with silk acquires a charge of 6×10^-12 C. Calculate the number of electrons it has gained or lost. (1)
2. If the magnitude of each charge becomes doubled, the separation between them is halved and the system of charges kept in a medium of=3 Calculate the force between them. (1)
3. If two equal charges separated by a distance of 2m in air medium experiences a force of 0.9×10¹⁰ C, Calculate the magnitude of each charge. (1)
4. Electric field intensity is 400Vm^-1 at a distance of 2 m from a point charge. At what distance it will become 100 Vm^-1? (1)
5. What will be the force experienced by a particle of charge 2µC placed in an electric field of 10kVm^-1? (1)
6. What is the work done by moving 400μF charge between two points separated by a distance of 27 cm on an equipotential surface? (1)
7. Calculate the number of electric lines of force from a charge 1.7708X10^-6 C in air medium? (1)
8. Two protons ‘A’ and ‘B’ are placed between two parallel plates having a potential difference ‘V’ as shown in the figure. Will these protons experience equal or unequal force? (1)
9. Draw an equipotential surface for a point charge q> 0(1)
10. The capacitance of a parallel plate capacitor is ‘C’. If 15 such capacitors are connected in series and then in parallel, what is the ratio of effective capacitance of first case to the second? (1)
11. What is electric polarization ,polar and non polar molecules?( 2)
12. 2) Define electrostatic induction and corona discharge. ( 2)
13. Calculate the ratio of force experienced by a proton to that of the electron placed in an electric field of 4KVm^-1. ( 2)
14. If an electrician has three capacitors of capacitances 4µF, 7µF& 12µF. How should he connect them, So that the effective capacitance will be 10µF? ( 2)
15. Define the SI unit of potential difference and charge. ( 2)
16. Two charges of 20µC and -20µC are placed 20 cm apart at points A and B respectively. Compute the electric field strength at point C, 20 cm away from both A and B.(3)
17. Three capacitors of capacitances 4µF, 6µF and 8µF are connected parallel to each other and the combination is connected across a battery of 25V. Calculate the charges present on each capacitor and the total charge flows from the source. (3)
18. Derive an expression for the torque experienced by a dipole in an external electric field. (3)
19. Obtain an expression for the capacitance of a parallel plate capacitor. (3)
20. Derive the relation E= (3)
21. Derive an expression for the potential at a point due to dipole. Write the special cases also.(5)
22. Derive an expression for ‘E’ at a point on the axial line of the dipole. (5)
23. Explain with a neat diagram the principle, construction and working of a Van de Graff generator. (5)

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Speed of sound

Why sound travels faster in humid air than normal air as humid air is denser than normal air? (Akash asked)

Answer:

The speed of sound in a medium is inversely proportional to the square root of its density. Humid air is less dense than dry air. Therefore the speed of sounf in humid air is greater than that in dry air.

Confused?

Are you thinking why dry air is more than that of humid air? This is a common misconception. Students used to think that humid air is denser than dry air. But it is not so. Just like skimmed milk (milk removed off its cream) is more dense than normal milk (with cream). Density of cream is much less than that of the rest of milk. So when it is removed, the residual milk becomes denser.

Humid air contains water vapor content. Water vapor is lighter than air. So when air contains water vapor, its density is less. When the water content is removed, it becomes denser.

Download sample question papers from CBSE

	Sample Question Paper for Class IX & X for Term II (Second Term – March 2012)
	Sample Question Paper, Syllabus and Guidelines for Class IX & X for Term I (First Term – Setember 2011)
	Sample Question Paper for Class IX & X for Term II (Second Term – March 2011)
	Sample Question Paper for Class IX & X for Term I (First Term, September 2010)
	Sample Question Paper for Board Exam 2012 (Class XII)
	Sample QP & Marking Schemes for Board Exam 2011 (Class XII)
	Previous Year Question Papers 2011 and Marking Scheme
	Previous Year Question Papers (2010) and Marking Scheme

Height of Antenna and range of transmission

A TV Tower has a height h. Derive expression for the maximum distance upto which signals can be received on earth.

Height of Antenna and Range of Transmission

What is meant by charge on a capacitor?

Mohit asked this question:

“What is meant by charge on a capacitor?”

Answer: As we know, a simple capacitor (say a parallel plate capacitor) consists of two plates parallel to each other. When charged, charge on either plate of the capacitor is called charge on the capacitor.

The following links will help you explore further and understand more

• http://www.kpsec.freeuk.com/components/capac.htm
• http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html
• http://www.youtube.com/watch?v=zNpbdptwxlQ
• http://www.youtube.com/watch?v=qdXbnhb1bVo&feature=related

Addition of vectors – can you add 3 unit vectors to get a unit vector ?

“Can you add 3 unit vectors to get a unit vector ? discuss in terms of velocity, force etc”

-Sindhuja posted

The answer is yes. Please find a detailed description on addition of vectors with examples and exercises at the following links.

• http://www.physchem.co.za/Vectors/Addition.htm
• http://www.physchem.co.za/Vectors/Physical%20Examples.htm
• http://www.physicsclassroom.com/class/vectors/u3l1b.cfm
• http://www.walter-fendt.de/ph14e/resultant.htm
• http://canu.ucalgary.ca/map/content/vectors/addition/explain/tiptail/
• http://www.physicsclassroom.com/morehelp/vectaddn/practice.cfm