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General Instructions:

  • All questions are compulsary
  • There are 30 questions in total. Questions 1 to 8 carry 1 mark each. Questions 9 to 18 carry 2 marks each. Questions 19 to 27 carry 3 marks each and questions 28 to 30 carry 5 marks each.
  • Use of calculators is not permitted.


******Choices are avoided as this is a question paper meant for practice ***********

********************* (more…)

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 ofclip_image002=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=clip_image004 (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)



Find below the links to questions papers in Physics already available at our group of Physics websites




















Collection of Problems received from Class 12 Physics

These problems were posted by Geena. Hope that we will be able to post the answers to these questions soon; each in a separate post. By the time visitors can attempt to post their answers as comments to this post. (Only selected posts will be published)


Please note that the answers are not published until the Physics teachers are not satisfied with the answers. So, please be patient to get the correct answers rather than approximations in a haste.

If you want real time answers to your queries by a group of Physics Lovers, you can post them at the Physics Fans group with facebook at https://www.facebook.com/groups/askphysics/

  1. A series battery of 10 lead accumulators each of emf 2 V and internal resistance 0.25 ohm is charged by a 220 V D.C. mains to limit the charging current a resistance of 47.5 ohm is used in series in the charging circuit. What is a) the power supplied by the mains and b) power dissipated as heat? Account for the difference of powers is (a) and (b).
  2. A potentiometer wire has a length L and a resistance Ro. It is connected to a battery and
    a resistance combination as shown. Obtain an expression for the potential drop per unit length of this potentiometer wire. What is the maximum emf of a ‘test cell’ for which one can get a ‘balance point’ on this potentiometer wire? What precaution should one take, while connecting this ‘test cell’ , in the circuit?
  3. A cell, of emf 4 V and .internal resistance 0.5 Ω, is connected across a load of resistance (i) 7.5 Ω, (ii) 11.5 Ω. Calculate (i) the ratio of the differences in the emf of the cell and the potential drop across the load, and (ii) the ratio of the currents in the two cases.
  4. In the figure shown, calculate the total flux of the electrostatic field through the spheres S1 and S2 The wire, AB, shown here, has a linear charge density, λ given by λ = kx where x is the distance measured along the wire, from the end A. diagram
  5. A straight wire, of length L, carrying a current I, stays suspended horizontally in mid air in a region where there is a uniform magnetic field B . The linear mass density of the wire is λ. Obtain the magnitude and direction of this magnetic field.
  6. Two cells of same emf E, but different internal resistance rl and r2 are connected to an external resistance R as shown. in the figure. The voltmeter V reads zero. Obtain an expression for R in terms of rl and r2. Calculate the voltage across the cell of internal resistance r2. (Assume that the voltmeter V is of infinite resistance).
  7. A galvanometer with a coil of resistance 120 ohm shows full scale deflection for a current of 2.5 mA How will you convert the galvanometer into an ammeter of range 0 to 7.5 A ? Determine the net resistance of the ammeter. When an ammeter is put in a circuit, does it read slightly less or more than the actual current in the original circuit? Justify your answer.
  8. diagram1 Figure shows a bar magnet M falling under gravity through an air cored coil C. Plot a graph
    showing the variation of induced e.m.f (E) with time (t). What does the area enclosed by the
    E – t curve depict ?
  9. The electron in the hydrogen atom circles around the proton with a speed of 2.18 x 106 m/s in an orbit of radius 5.13 x 10 -11 m. What magnetic field does it produce at the centre?
  10. A proton moves with a speed of 7.45 x 105 m/s directly towards a free proton originally at rest. Find the distance of the closest approach for the two protons. (Given: mass of proton = 1.67 x 10–27 kg and e = 1.6 x 10 –19 C)
  11. diagram2 Figure (a), (b) and (c) show three a.c. circuits in which equal currents are flowing. If the frequency of emf be increased, how will the current be affected in these circuits? Give reason for your answer.

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Difference between Scalar Product and Vector Product

“What is the difference between dot product and cross product?” [The question was posted by Salman)

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How atoms are formed? – Neeraj Asks

Neeraj asks: ”We have read that atoms can neither been created nor been destroyed!
I want to know from where atoms came in existence,if they can not been created,also atom contain electron and proton which are negatively and positively charged,i want to know from where these charge came?”


Your question will be answered soon

Where is electricity stored after it is generated but before it is supplied? (Chat Transcript from FaceBook)

Where is electricity stored after it is generated but before it is supplied?
    • Mahesh Sable Electrical power cannot be stored and,therefore,power plants must produce power as and when demanded.power stations r connected in parallel hence load is equally distributed,electric Power can be adjusted with help of step up or step down transformers.


    • Mathew Abraham Transformer does not increase power


    • Chitraja Rajan The demand for electricity varies randomly within a day itself…so there should be something which should be adjusted according to the demand.


    • Vishnu Mohan G huge capacitors? i think i read somewhere like this.


    • Rajat Sharma

      Hi All, the question is very smart, i think electricity stored before generation is stored in Water(DAM), Uranium Rods(Nuclear), HydroCarbons(Coal, GAS). Electricity can only store when it is in Direct Current format like in Batteries, Capacitor(its a very small time to store/release) Well there are many source where we can store electricity. When electricity is in demand then Power generation takes place within huge Alternators, this powers generation takes places in terms of Phase Shift between all the power Houses across the country, if this phase shift is disturb then power grid fails. after this the transformers come into picture so as to reduce Resistance loses.



    • Kannan Kannan Ps in my little knowledge electricity unable to store continuing process of generater get current


    • Chitraja Rajan at the generation side electricity is high ac current ..if it is converted into dc then there should be large containers to store them and also need suitable convertors to convert it in either form every time


    • Mathew Abraham In modern generators, there are equipment to control the rate of flow of water and in turn rate of rotation as well as the power generated. SO, it is quite right to say that electricity is generated as and when required. When you switch on a device power generation also increases until it reaches maximum capacity. Thereafter we will get less power. Remember the low voltage we suffer during the evening when the power consumption is maximum a few seconds ago · Like

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