Tuesday, 9 January 2018

CBSE CLASS 12 PHYSICS REVISION QUESTION PAPER BASED ON VOLUME II

XII                                                PHYSICS                                                                                                                                                                                                                          MARKS: 70
                                                                                                                                                                                                                                                                                                    DURATION:3 Hrs

The entire question was compulsory and there were 26 questions. The question paper was having been divided in to five sections: Section A, Section B, Section C, Section D, Section E.
Section A – The section had five questions which carried one marks each. 
Section B – The section had five questions which carried two marks each. Where question no 10 were having options either one of them you have to choose.
Section C- The section had 12 questions which carried three marks each and the questions were descriptive and application based. Where question no – 18 were having options either one of them you have to choose.
Section D- Contains one value based question of four marks.
Section E – The section had three questions which carried five marks each. Where the entire question no – 24, 25, 26 were having options either one of them you have to choose
SEC A
 1.A metal emits photoelectrons when red light falls on it. Will this metal emit photoelectrons when blue light falls on
it? Why?
2. Name the series of hydrogen spectrum which has least wavelength.
3. What is the ratio of velocities of electron in I, II and III Bohr Orbits?
4. At what temperature does a semiconductor behave as an insulator?
5. What is the least size of an antenna required to radiate a signal of wavelength?
SEC B
6. Define Brewster’s angle. Show that the Brewster’s angle iB for a given pair of media is related to critical angle ic through the relation ic = sin-1(cot iB)
7. Two independent light sources cannot act as coherent sources. Why?
8. Define distance of the closest approach. An α particle of kinetic energy K is bombarded on a thin gold foil. The distance of the closest approach is  r.What will be the distance of closest approach for an α particle of double the kinetic energy?
9. The diagram shows a piece of pure semiconductor S in series with a variable resistor R and a source of constant voltage V. Would you increase or decrease the value of R to keep the reading of ammeter A constant, when semiconductor S is heated ? Give reason.


10. Why is a photo diode used in reverse bias ?
                          OR
Write the truth table for the combination of gates shown.





SEC C
11. Complete the ray diagram in the following figure where, n1 is refractive index of medium and n2 is refractive index of material of lens.

12. Explain briefly (i) sparkling of diamond (ii) use of optical fibre in communication.
13. In double slit experiment SS2 is greater than SS1 by 0.25l. Calculate the path difference between two interfering beam from S1 and S2 for minima and maxima on the point P as shown in figure.


14. An object is placed in front of a concave mirror of focal length 20 cm. The image is formed three times the size of the object. Calculate two possible distances of the object from the mirror.
15. What is depletion region in p-n junction diode. Explain its formation with the help of a suitable diagram.
16. What is rectification ? With the help of labelled circuit diagram explain half wave rectification using a junction diode.
17. Explain the following terms :
(1) Ground waves
(2) Space waves
(3) Sky waves
18. A T.V. Tower has height of 70 m.
(i) How much population is covered by the T.V. broadcast if the average population density around the tower is 1000 km-2 ? Radius of earth is 6.4 × 106 m.
(ii) By how much should the height of the tower be increased to double the coverage area ?
OR
A communication system is operating at wavelength l = 750 nm. If only 1% of the frequency is used as channel bandwidth for optical communication then find the number of channels that can be accommodated for transmission of(i) an Audio signal requiring a bandwidth of 8 kHz. (ii) a Video T.V. signal requiring a bandwidth of 4.5 kHz.
19. State the law of radioactive decay. Deduce the relation N = N0e-lt, where symbols have their usual meaning.
20. What is the (i) Speed (ii) Momentum (ii) de-Broglie wavelength of an electron having kinetic energy of 120eV?
21. Why wave theory of light could not explain the photoelectric effect? State two reasons.
22. An electron and a proton are possessing same amount of K.E., which of the two have greater de-Broglie,   wavelength? Justify your answer. 
 SEC D
23. Dev is a good student and studied semi-conductors and electronic devices in school. He also used many semi-conductor devices like LED TV.s, radio etc. He saw his monthly bill of CNG/LPG and discussed with his father that the cost was going up. To cope up with the future he suggested using solar devices. His father also agreed using solar devices.(a) What are the values developed by Dev ? (b) Which materials (any two) would be suitable semi-conductor forusing solar energy ? (c) Explain the working of a solar cell.


SEC E
24. (i) In Young’s double slit experiment, deduce the conditions for (a), constructive, and (b) destructive interference at a point on the screen. Draw a graph showing variation of intensity in the interference pattern against position x on the screen. (ii) Compare the interference pattern observed in Young’s double slit experiment with single slit diffraction pattern, pointing out three distinguishing features.

                                                                                                          OR
(i) Plot a graph to show variation of the angle of deviation as a function of angle of incidence for light passing through a prism. Derive an expression for refractive index of the prism in terms of angle of minimum deviation and angle of prism.
(ii) What is dispersion of light? What is its cause?
(iii) A ray of light incident normally on one face of a right isosceles prism is totally reflected as shown in fig. What must be the minimum value of refractive index of glass? Give relevant calculations.


25. State the condition under which the phenomenon of diffraction of light takes place. Derive an expression for the width of the central maximum due to diffraction of light at a single slit. Also draw the intensity pattern with angular position.
OR
Draw a labelled ray diagram of a compound microscope and explain its working. Derive an expression for its magnifying power.
26. Draw a circuit diagram to study the input and output characteristics of an n-p-n transistor in its common emitter configuration. Draw the typical input and output characteristics and explain how these graphs are used to calculate current amplification factor of the transistor.                         
                                                                                       OR

Two signals A, B as given below are applied as input to (i) AND (ii) NOR and (iii) NAND gates. Draw the output waveform in each case.


Tuesday, 2 January 2018

CBSE CLASS 11 PHYSICS REVISION QUESTION PAPER


Class XI Physics
REVISION
Time: 3 hours                                                                                  Maximum Marks: 70
General Instructions:
(i) All questions are compulsory. There are 26 questions in all.
(ii) This question paper has five sections: Section A, Section B, Section, Section D and
Section E.
(iii) Section A contains five questions of one mark each, section B contains five questions
of two marks each, section C contains twelve questions of three marks each, section
D contains one value based question of four marks and section E contains three
questions of five marks each.
(iv) There is no overall choice. However, an internal choice has been provided in one
question of two marks, one question of three marks and all the three questions of five
marks weightage. You have to attempt only one of the choices in such questions.

SEC A
1. Lubricants are used between the two parts of a machine. Why ?.
2. Where is the centre of mass of a meter stick?
3. Why does a gun recoils when a bullet is being fired ?
4. Why is it difficult to catch a cricket ball than a tennis ball even when both
are moving with the same velocity ?
5. Which spring has greater value of spring constant – a hard spring or a delicate
spring ?
SEC B
6. Define angle of friction and angle of repose.
 7. Why does a speedy motor cyclist bends towards the centre of a circular path
    while taking a turn on it ?
 8. The outer edge of a curved road is generally raised over the inner edge.
     Why?
 9. Two springs A and B are identical except that A is harder than B (KA > KB) if these are
   stretched by the equal force. In which spring will more work be done ?
 10. How much work is done by a railway porter walking on a horizontal platform with
    a load on his head ? Explain.OR
Explain that gravitational force is a conservative force.

SEC C
11. Derive  the expression for rotational kinetic energy of a rigid body rotates with angular velocity ѡ and moment of Inertia I.

12. How high must a body be lifted to gain an amount of P.E. equal to the K.E. it has when
     moving at speed 20 ms–1. (The value of acceleration due to gravity at a place is 9.8 ms–2).
13. State and prove work energy theorem.
14. 20 J work is required to stretch a spring through 0.1 m. Find the force constant of the spring.
     If the spring is further stretched through 0.1 m. Calculate work done.
15. A spring balance is attached to the ceiling of a lift. When the lift is at rest
spring balance reads 49 N of a body hang on it. If the lift moves :
(i) Downward
(ii) upward, with an acceleration of 5 ms–2
(iii) with a constant velocity.
What will be the reading of the balance in each case ?

16. A block placed on a rough horizontal surface is pulled by a horizontal force
F. Let f be the force applied by the rough surface on the block. Plot a graph
of f versus F.
17. A block slides down as incline of 30° with the horizontal. Starting from rest, it covers 8 m in the first 2 seconds. Find the coefficient of static friction.
8. Derive an expression for K.E. of a body of mass ‘m’ moving with velocity ‘v’ by calculus method.
18. Give the physical significance of moment of inertia. Explain the need of fly wheel in Engine.
19. Three masses 3 kg, 4 kg and 5 kg are located at the corners of an equilateral triangle of side 1 m. Locate the centre of mass of the system.
20. What is the turning effect of force called for ? On what factors does it depend ?
21.What do you mean by Radius of  gyration? Derive the expression for Radius of gyration.

22 .A truck of mass 1000 kg accelerates uniformly from rest to a velocity ofs–1 in 5 seconds. Calculate (i) its acceleration, (ii) its gain in K.E.,
SEC D

 23.       
Suresh noticed a big Granite Rock in his locality. He thought that if they worked upon it they could earn money. He took permission from the Government, completed all the formalities .He broke the Rock using a bomb. The rock was made into slices .They established a Granite industry. Many of the people in the surroundings started to earn and live comfortably. (a) What values of Suresh impress you? (b)A bomb is thrown in a horizontal direction with a velocity of 50 m/s. It explodes into two parts of masses 6 Kg and 3 Kg. the heavier fragment continues to move in the horizontal direction with a velocity of 80 m/s .Calculate the velocity of the lighter fragment.



SEC E

24.Show that at any instant of time during the motion total mechanical energy
     of a freely falling body remains constant. Show graphically the variation of K.E. and P.E.
    during the motion.
                                                                               OR
25.How does a perfectly inelastic collision differ from perfectly elastic collision? Two particles
   of mass m1 and m2 having velocities U1 and U2 respectively make a head on collision. Derive
    the relation for their final velocities. Discuss the following special cases.
    (i) m1 = m2
    (ii) m1 >> m2 and U2 = 0
    (iii) m1 << m2 and U1 = 0
                                                                                OR
    Define spring constant, write the characteristics of the force during the elongation of a spring.
    Derive the relation for the P.E. stored when it is elongated by X. Draw the graphs to show the
    variation of P.E. and force with elongation.

26. With the help of suitable example, explain the terms static friction, limiting friction and
       kinetic  friction. Show that static friction is a self adjustingforce.
                                                                            OR
    a)State Newton’s Second law
       There are few forces acting at a Point P produced by strings as shawn,which is at rest, Find
       the forces F1 & F2





















CBSE CLASS 12 PHYSICS REVISION QUESTION PAPER



Class XII Physics
REVISION
Time: 3 hours                                                                                                Maximum Marks: 70

General Instructions:
(i) All questions are compulsory. There are 26 questions in all.
(ii) This question paper has five sections: Section A, Section B, Section, Section D and
Section E.
(iii) Section A contains five questions of one mark each, section B contains five questions
of two marks each, section C contains twelve questions of three marks each, section
D contains one value based question of four marks and section E contains three
questions of five marks each.
(iv) There is no overall choice. However, an internal choice has been provided in one
question of two marks, one question of three marks and all the three questions of five
marks weightage. You have to attempt only one of the choices in such questions.

SECTION A
1. State the factors on which the refractive index of a material medium for a given wavelength depends.
2. Sketch the emergent wavefront


3. The instantaneous current and voltage of an a.c circuit are given by
i= 10 sin 314t Ampere,
v= 50 sin 314t Volt.
What is the power factor of the a.c. circuit?
4. How does power of convex lens vary when red light incident on it is replaced by violet light?
5. The vertical component of Earth’s magnetic field at a place is √3 times the horizontal component. What is the angle of dip at this place?
SECTION B

6.(a)An alternating voltage E = Eo sinωt is applied to a circuit containing a resistor R connected in series with a black box. The current in the circuit is found to be I = Io sin (ωt + π/4).


(i) State whether the element in the black box is a capacitor or inductor.
(ii) Draw the corresponding phasor diagram and find the impedance in terms of R.


7. The magnetic field in a plane electromagnetic wave is given by: By = 12 × 10–8 sin (1.20 × 107 z + 3.60 × 1015 t) T.
Calculate the
(i) Energy density associated with the Electromagnetic wave
(ii) Speed of the wave
OR
What is dispalcemeny current? Write Maxwell’s Equations
8. A spherical convex surface of radius of curvature 20 cm, made of glass (μ = 1.5) is placed in air. Find the position of the image formed, if a point object is placed at 30 cm in front of the convex surface on the principal axis.


9. State one use of each of the following e.m. waves? Arrange them in the decreasing order of
their frequency.
i. X-rays
ii. Radio waves
iii. Microwaves
iv. Ultraviolet light.
10. Define the following:
i. Geographic meridian
ii. Magnetic meridian

SECTION C
11. Figure shows a metal rod PQ of length l, resting on the smooth horizontal rails AB positioned between the poles of a permanent magnet. The rails, rod and the magnetic field B are in three mutually perpendicular directions. A galvanometer G connects the rails through a key ‘k’. Assume the magnetic field to be uniform. Given the resistance of the closed loop containing the rod is R.


(i) Suppose K is open and the rod is moved with a speed v in the direction shown. Find the polarity and the magnitude of induced emf.
(ii) With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ even though they do experience magnetic force due to the motion of the rod. Explain.
(iii) What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?


12.With the help of a diagram, explain the principle of a device which changes a low voltage into a high voltage but does not violate the law of conservation of energy. Give any one reason why the device may not be 100% efficient.

13. In a double slit experiment, the distance between the slits is 3 mm and the slits are 2 m away from the screen. Two interference patterns can be seen on the screen one due to light with wavelength 480 nm, and the other due to light with wavelength 600 nm. What is the separation on the screen between the fifth order bright fringes of the two interference patterns?
14. What do you understand by the statement ‘Light from the sun is unpolarised’.
Explain how does sunlight gets polarized by the process of scattering?
15. In a series LCR circuit connected to a variable frequency 230 V source L=5.0H, C=80 μF and R=40 Ω.
(i) Obtain the amplitude of current at the resonating frequency.
(ii) Show that the potential drop across the LC combination is zero at the resonating frequency.
16.Derive lens makers formula with suitable diagram for a thin convex lens.
17. Draw a ray diagram showing the image formation by a reflecting type telescope. Give two advantage of reflecting type telescope over the refracting type telescope.
OR
Write the expression for the resolving power of a microscope. How does the resolving power of compound microscope change when (i) wavelength of light used is increased (ii) Diameter of the objective lens is increased.
18. A circular coil of radius 10 cm, 500 turns and resistance 2Ω is placed with its plane perpendicular to the horizontal component of the earth’s magnetic field. It is rotated about its vertical diameter through 1800 in 0.25 s. Estimate the magnitude of the emf and current induced in the coil. Horizontal component of the earth’s magnetic field at the place is 3.0 X 10-5 T.
19.An a.c source of voltage V = Vm sin ωt is connected one –by-one to three elements X,Y and Z. It is observed that the current flowing in them
(i) Is in phase with applied voltage for X
(ii) Lags the applied voltage in phase by π/2 for element Y.
(iii) Leads the applied voltage in phase by π/2 for element Z.
When three elements X, Y and Z are connected in series with the a.c source then at a particular frequency current in the circuit become maximum. Write the condition for the maximum current in the circuit and obtain the expression for the frequency at that condition.
20. State the difference between dia, para and ferro magnetic materials in terms of their (i) behavior in a non uniform field (ii) behavior in a uniform field (iii) relative permeability (iv) susceptibility and (v)temperature dependence of their susceptibility
21. What is total internal reflection? State two important use of it. Where does in nature this phenomenon can be observed?
22.Derive the expression when a ray of monochromatic light passes through a glass prism.
                                                                       SECTION D
23.Akil was playing cricket with his friends, when a ball hit his friend Bharat on his left leg .Bharat screamed with pain.Akil rushed towards him and comforted him and asked him not to move his
leg. He quickly took out his cell phone and called up Bharat’s parents and briefed them about the incident. In10 minutes Bharat was taken to the nearby hospital and was examined by the doctor who advised for an X-rays test which confirmed a hairline fracture.
A) How are X-rays produced?
b) Mention one another application of X rays.
c) Mention two qualities of Akhil which are reflected from the above situation.
SECTION E

24.(a)Draw a ray diagram of compound microscope for the final image formed at least distance of distinct vision?

(b) An angular magnification of 30X is desired using an objective of focal length 1.25 cm and an eye piece of focal length 5 cm. How will you set up the compound microscope for the final image formed at least distance of distinct vision?

OR
(a) Draw a ray diagram of an astronomical telescope for the final image formed at least distance of distinct vision?
(b) An astronomical telescope has an angular magnification of magnitude 5 for distant objects. The separation between the objective and an eye piece is 36 cm and the final image is formed at infinity. Calculate the focal length of the objective and the focal length of the eye piece?
25. Using Huygen’s construction of a wave front, explain the reflection of a plane wave front at a plane surface. Draw the shape of the refracted wave front when a plane wave front is incident on (i) convex mirror (ii) concave mirror. Illustrate with the help of diagrams the action of convex lens and concave lens on a plane wave front incident on it.
OR
(a)State the essential condition for the diffraction of light to take place. A parallel beam of monochromatic light falls normally on a narrow slit and light coming out of the slit is obtained on the screen. Derive an expression for the angular width of the central bright maxima obtained on the screen.
(b)‘Diffraction defines the limit of ray optics’. Give a brief explanation of this statement.
26.What is mutual induction? Define the coefficient of mutual induction and its SI unit. Also, derive an expression for coefficient of mutual induction of two long solenoids.
OR
a)State Lenz’s law . Derive an expression for induced emf developed in a conductor of length l moving with velocity u in a transverse magnetic field of Strength B.
b) What are Eddy Currents? State the main undesirable effect of these currents and give the method used to minimize the undesirable effect. Write any two applications of eddy currents.