Break HW
Session 2014 – 15
Dated :- 28.09.2014 to 07.10.2015
CLASS - XII
Q1. . An electric dipole is held in a uniform electric field (i) using suitable diagram show that it does not undergo any translatory motion and (ii) drive an expression for the torque acting on it and specify its direction.
Q2. State Gauss’s theorem & apply this theorem to obtain an expression for the electric field intensity at a point due to (i)an infinitely long uniformly charged straight wire (ii) a uniformly charged infinite sheet (iii) a uniformly charged thin spherical shell at an (a) outside point (b) inside point.
Q3. (a)Deduce an expression for the capacitance of a parallel plate capacitor with air as the medium between the plates (b)A dielectric slab of thickness‘t’ is kept in between the plates each of area A of parallel plate capacitor separated by a distance of‘d’. Drive an expression for the capacitance of capacitor for t <<d.
Q4. (i) Explain briefly how a capacitor stores energy on charging. Obtain expression for energy stored (ii) A parallel plate capacitor of plate separation’s’ is charged to a p.d. ‘V’. A dielectric slab of thickness d and dielectric constant K is introduced between the plates while the battery remains connected to the plates.
(a) Find the ratio of energy stored in the capacitor after and before the dielectric in introduced, give physical explanation for this change in stored energy.
(b) What happens to the charge on the capacitor?
(c)How does the electric field between plates change.
Q5. In a Van de Graaff type generator a spherical metal shell is to be a 15 × 10
6 V electrode. The dielectric strength of the gas surrounding the electrode is 5 × 10
7
Vm –1 . What is the minimum radius of the spherical shell required? (You will learn from this exercise why one cannot build an electrostatic generator using a very small shell which requires a small charge to acquire a high potential.) [Ans 30cm]
Q6. A parallel plate capacitor with air as dielectric is connected to a power supply and charged to a potential difference Vo. After disconnecting from power supply, a sheet of insulating material is inserted between the plates completely filling the space between them. How will its (i) charge on the plates (ii) electric field between the plates (iii) potential difference between the plates (iv) capacitance (v) energy stored in the capacitor.
Q7. (a) Describe the formula for the equivalent EMF and internal resistance for the parallel combination of two cells with EMF E
1 and E
2
 and internal resistances r
1 and r
2 respectively.
(a)What is the corresponding formula for the series combination?
(b) Two cells of EMF 1V, 2V and internal resistances r
2
and r
1
respectively are connected in (i) series, (ii) parallel. What should be the external resistance in the circuit so that the current through the resistance be the same in the two cases? In which case more heat is nerated in the cells?
Q8. Deduce the condition for balance in a Wheatstone bridge. Using the principle of
Wheatstone bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the circuit diagram and write the formula used. Write any two precautions.
Q9 . Describe the principle and construction of potentiometer. Explain how a potentiometer can be used to compare the emfs of two primary cells?
Q 10. Draw Circuit diagram for a meter bridge to determine the unknown resistance of a resistor. Obtain the balance condition for a meter bridge. Find the shift in the balance point for a meter bridge when two resistors in its two gaps, are interchanged.

Q 11. Are the paths of e’s straight lines between successive collisions in the (i) absence of electric field (ii) presence of electric field. Establish a relation between drift velocity and current. Hence obtain the relation between current density and drift velocity.
Q12. With the help of a neat and labeled diagram, explain the underlying principle and working of a moving coil galvanometer. What is the function of (i) uniform radial field (ii) Soft iron core?
A: (i) The torque on the coil is same in all positions of coil in the radial magnetic field. This provides a linear current scale.
(ii) Due to high permeability of soft iron, the magnetic field line crowd through the soft iron.
This increases the magnitude of magnetic field and makes it radial. Hence sensitivity of galvanometer increases.
Q13. Derive a mathematical expression for the force per unit length experienced by each of the two long current carrying conductors placed parallel to each other in air. Hence define one ampere of current. Explain why two parallel straight conductors carrying current in the opposite direction kept near each other in air repel.
A: Each current carrying conductor produces magnetic field around it. So each conductor experiences a force due to the magnetic field of the other. According to Fleming’s left hand rule, the direction of the force is perpendicular to the two wires and is outwards. Hence the two wires repel each other.
Q14. Draw a neat and labeled diagram of a cyclotron. State the underlying principles and explain how a positively charged particle gets accelerated in this machine. Show mathematically that the cyclotron frequency does not depend upon the speed of the particle.
Q15. State the Biot-Savart’s law for the magnetic field due to a current carrying element. Use this law to obtain a formula for magnetic field at the center of a circular loop of radius R carrying a steady current I. Sketch the magnetic field lines for a current loop.
Q16. (i) Using Biot-Savart’s law, derive the expression for the magnetic field due to a current carrying circular loop of radius R, at a point which is at a distance x from its center along the axis of the loop.
(ii) Two small identical circular loops, carrying equal currents are placed with the geometrical axes perpendicular to each other as shown in the figure.
Find the magnitude and direction of the net magnetic field produced at the point O.
Q17. Using Kirchoff’s laws, calculate the potential difference across the 8 ohm resistor.
[Ans : Current through resistance 8

= 0.46A, P. d. = 3.68Volts]
Q18. E
2
=1.02V, PQ=1m.When switch S open, null position is obtained at a distance of 51 cm from P. Calculate (i) potential gradient (ii) emf of the cell E
1
(iii) when switch S is closed, will null point move towards P or Q. Give reason for your answer.
[Ans: (i) Potential gradient k = 0.02V/cm (ii) emf of the cell E
1
= 2V
(iii) When switch S is closed, null point is not affected because no current drawn from cell E
1 at the null point. ]
Q19. In the potentiometer circuit shown, the balance point is at X. State with reason, where the balance point will be shifted when (i) R is increased; (ii) S is increased, keeping R constant. (ii) Cell P is replaced by another cell whose emf is lower than that of cell Q.
Q20. Two identical plane metallic surfaces A and B are kept parallel to each other in air separated by a distance of 1 cm as shown in figure.
A is given a positive potential of 10V and the outer surface of B is earthed. (i) What is the magnitude and direction of the uniform electric field between Y and Z? (ii) What is

the work done in moving a charge of 20 C from X to Y?
Ans : (i) E = 1000 V/m, direction from A to B
(ii) Zero.
Q21. The following data was obtained for the dependence of the magnitude of electric field, with distance, from a reference point O, within the charge distribution in the shaded region.
Field Point A B C A’ B’ C’
E/16 E/54 Magnitude of electric field
E E/8 E/27 E/2
(i) Identify the charge distribution and justify your answer.
(ii) If the potential due to this charge distribution, has a value V at the point A, what is its value at the point A’?
Q22.
Use Gauss’s law to obtain an expression for the electric field due to an infinitely long straight uniformly charged wire.
Electric field in the above figure is directed along + X direction and given by E x
= 5Ax + 2B, where E is in NC
-1 and x is in metre,
A and B are constants with dimensions
Talking A=10NC -1 m -1 and B = 5NC -1 calculate. (i) the electric flux through the cube. (ii) net charge enclosed within the cube.
[Ans (i ) 0.05Nm
2
/C (ii) 44.25X10
-14
C ]
Q23. Two point charges of charge values Q and q are placed at distance x and x/2 respectively from a third charge of charge value 4q, all charges being in the same straight line. Calculate the magnitude and nature of charge Q such that the net force experienced by the charge q is zero . [Ans Q = q/4 , +ive ]
Q24. How will a dia, para and ferromagnetic material behave when kept in a non-uniform external magnetic field? Name two main characteristics of a ferromagnetic material which helps us to decide its suitability for making (i) a permanent magnet and (ii) an electromagnet. Which of these two characteristic should have a high or low values for each of these two types of magnets?
Q25. A short bar magnet placed with its axis inclined at 30
0 to the external magnetic field of 800 G acting horizontally experiences a torque of 0.016 Nm. Calculate - (i) the magnetic moment of magnet (ii) the work done by an external force in moving it from most stable to most unstable position. (iii) What is the work done by the force due to the external magnetic field in the process mentioned in (ii)?
A: (i) m = 0.4 Am2
(ii) Most stable position = 0
0 and most unstable position = 180
0
,
W = - mB (cos 180 – cos 0) = 2mB = 0.64J
(iii)W = - 0.64J.
Q26 Total capacitance of the combination between A and B in the given figure is 15μF. Calculate the capacitance of capacitor C.
[ Ans. 60 μ F]
Q27. On charging a parallel plate capacitor to a potential V, the spacing between the plates is halved, and a dielectric medium of r

= 10 is introduced between the plates, without disconnecting the d.c source. Explain using suitable expressions, how the (i) capacitance (ii) electric field (iii) energy density of the capacitor change.
[Ans(i) C1= 20 Co ( ii ) E 1= 2 Eo ( iii ) u1 = 40 uo

]
Chemistry

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Polscience
th
Eco

English
Q1.
(a) Read at least two short reports in any English newspaper. Cut and paste them on your note-book. On the basis of your reading of these reports, make notes on them in points only, using headings and sub-headings. Use recognizable abbreviations wherever necessary.
(b) Make a summary of these passages in not more than 80 words and also suggest a suitable title.
Q2 . K.P.Mittal of 11-B, Mebin Street, Delhi seeks full time job in a reputed but decent organization. Draft a suitable advertisement to be published in the Situation Wanted column of a national daily giving necessary details. Invent other details yourself.
Q3 . Write a formal reply to Mrs. and Mr. Chawla regretting your inability to attend the birthday function of their son due to a prior engagement.
Q4.
During the Autumn break, a team of school students from KendriyaVidyalaya, New
Delhi visited a village named Kishanpur. The team was much worried on noticing the most pitiable insanitary conditions prevailing there. The team collected the villagers and its leader Mr. Manjeet, gave a short speech on the necessity and benefits of remaining clean. Write the speech in about 200 words.
Q5.
You are the President of your school Drama Club. Your club is organizing a play
‘The Invisible Man’ to help the victims of floods in Kashmir. Design a poster informing the students about this play. Invent necessary details.
Q6 .You are Pawan/ Parkhi, the librarian of the school library. You have been asked to place an order for children’s story books for the age group 10 - 16. Write a letter to
Modern Book Depot, NaiSarak, Delhi placing an order for the books. Invent the necessary detail.
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Geography
2014-15
Autumn Break
Holiday Home Work
th

Hindi
कककककककक कककककककक कक कक कककक , कक कककककक
कककककककक ककककक
कककक कक ( ककककककक कककक )
ककककक – कक
ककककक ककककक
अ अअअअअअअअअ अअअ अअ अअअअ
अ - अअअअ अअ अअअअअ / अअअअ अअअअअअ
अ - अअअअअअअ
अ - अअअअअअअ अअ अअअअअअअअअअअअअअ
अ अअअअअ अअअअअअ – अअ अअअअअअ ( अअअ अअअअ (
१
अअअअअ अअअअअअ ( अअअअअअ अअअअ (
History
2014-15
th

1) Do revision of book 1 st ,2 nd & 3 rd (Chapter 1 st ,2 nd ,3 rd )
2) Read all themes of chapter number -(12 to 15 chapters)
3) Map work – Complete all the map of Book number 1 st , 2 nd ,& 3 rd .
4) Project work: - Collect maximum information regarding theme given to each group.
Maths
2014-15
th

1 Find a unit vector perpendicular to the plane of triangle ABC where the vertices are A (3,
–1, 2) B (1,–1, –3) and C (4, –3, 1).
2 . In a regular hexagon ABCDEF if AB = a and BC = b then express CD , DE , EF , FA , AC AD , AE and
CF in terms of a and b .
3 If
 a

 b
 a

,
 c
 b ,
 c are mutually perpendicular vectors of equal magnitudes, show that the vector
is equally inclined to
 a ,
 b and
 c .

Ques 1. i, j, k are unit vector along
coordinate axes
a = 3i – j
b = 2i + j – 3k
Then express b = b1 + b2 such that
b1IIa and b2 perp b
Ques 2. If a, b, c are mutually perpendicular
vectors of equal magnitude show
that a+ b + c is equally inclined to
a, b and c
Ques 3. Let a = i + 4j + 2k b = 3i – 2j + 7k
c = 2i – j + 4k
For vector d perp to both a & b and c.d =15