## Monday, 12 February 2018

### CBSE CLASS10 PHYSICS IMPORTANT QUESTIONS 2017 -2018

CBSE CLASS 10 PHYSICS CHAPYERWISE IMPORTANT QUESTIONS  2017-2018
LIGHT REFLECION AND REFRACTION
ONE MARK QUESTION
1. Refractive index of water is 4/3 and that of the glass is 3/2 with regard to air. What is the refractive index of glass with respect to the water? What is the power of concave lens of focal length 200cm?
2. The radius of curvature of spherical mirror is 20cm.What is its focal length?
3. What is the angle of reflection when a ray of light falls normally on a plane mirror?
4. What is the magnification produced by the plane mirror?
5. What is the nature of image formed by concave mirror if magnification produce by mirror is +3.
6. If the speed of light in a medium id 2 x 108 m/s, then what is refractive index
7. The refractive index of diamond is 2.42. What is the meaning of this statement in relation to the speed of light?
8. What do you mean by Power of the lens?
TWO MARKS QUESTION
9. The power of the lens is -2D .What is the focal length and nature of the lens?
10. An object 2cm high produce areal image 3 cm high , when placed at a distance of 15cm from concave mirror. Calculate the position of the image..
11. The power of a focal length is – 4D.State the nature of lens and any two characteristics of the image formed by the lens.
12. State two examples based on phenomenon of refraction of light in everyday life situation.
13. Distinguish between real and virtual image.
14. Name the type of mirror used in the following situations: a) Headlights of car b) rear – view mirror of vehicles
15. An object is placed at a distance of 10 cm from convex mirror of focal length 15 cm. Find the position and nature of image.
16. Define: 1) Snell’s law of refraction of light. 2) Pole of a concave mirror.
17. (a) we prefer to use a convex mirror as a rear view mirror in vehicles. Why ?
18. State a condition for no refraction of light when light enter from one medium to another.
THREE MARKS QUESTION
19. The refractive indices of alcohol and turpentine oil with respect to air are 1.36 and 1.47 respectively. Find the refractive index of turpentine oil with respect to alcohol. In which of the two media the speed of light will be more.
20. a )Define power of a lens and give its unit. b) A convex lens forms a real and inverted image of needle at a distance of 50cm from it. Where is the needle placed in front of this lens if the size of the image is equal to the size of the object? Also find power of the lens
21. Two thin lenses of focal lengths +20 cm and – 15 cm are kept in contact. What is the focal length and power of the combination?
22. An object 2 cm high is placed at a distance of 16 cm from a concave mirror which produces a real image 3cm high. (a) Find the position of the image (b) What is the focal length of mirror?
23. Using lens formulae, find the position of image, its nature
24. An object is placed at a distance of 10cm in front of convex mirror of focal length 15cm. find the nature and position of image.
25. Draw a ray diagram and show the image formed by a concave mirror when the object is kept at focus.
26. Two thin lenses of power +3.5D and -2.5 D are placed in contact. Find the power & focal length of lens combination ?
27. Define magnification. Write the sign convention used for expressing it. and find magnification formed by a concave lens of focal length 20cm and the object is at 15cm.
28. What is the lens formula? Write the sign convention for various mirror and lens.
29. Name the lens/ mirror in the following situations; i) Rear View mirror ii) magnifying Glass iii) Mirror with Dentist iv) Correction of Myopia
FIVE MARKS QUESTION
30.Draw a ray diagram in each of the following cases to show the formation of an image, when an object is placed (a) Between optical centre and principal focus of a convex lens. b) Between F and 2F of concave lens c) At 2F of convex lens
31. Write the characteristic of image formed in each case.
32. A 1 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20cm.The distance of the object from the lens is 15cm.Find the nature, position, size and magnification of the image.
33. Find the size, nature and position of image formed when an object of size 1 cm is placed at a distance of 15 cm from concave mirror of focal length 10 cm.
34. Draw the ray diagram for the different positions of the images formed by concave mirror.

HUMAN EYE AND COLOURFULL WORLD
ONE MARKS QUESTION
1. What is the far point and near point of the human eye with normal vision?
2. List the three phenomenon of light which is responsible for the formation of the rainbow in sky?
3. Name the place where the image is formed in the eye?
4. Name the muscular diaphragm that controls the size of the pupil.
5. What is the cause of dispersion of light?
6. Give the cause of cataract of eye.
7. Which color has got more wavelengths?
8. What makes bees respond to ultraviolet light?
9. What is the focal length of a plane mirror?
10. Which of the two has a great power, a lens of shot focal length or a lens of large length?
11. What does m= +1 stand for?
12. What is the power of a lens if its focal lenth is 50cm?
13. What is the nature of image at retina?
14. Name the point inside the lens through which a ray of light goes deviated?
15. What is the S.I. unit of power of a lens?
16. Name the photographic film equivalent to our eye .
17. Why does a glass slab not disperse white light?
18. Why do we not perceive the depth of a lake ?
19. Name two causes of Myopia, Hypermetropia and presbiopia.
20. Name the liquids that keep our eye soft.
21. What causes rainbow formation?
22. What is Mirage?
TWO MARKS QUESTION
23. Why are ‘danger’ signal lights red in colour?
24. Give reasons why the planets do not twinkle.
25. What do you mean by far point and near point of eye?
26. What is presbyopia? State the cause of it and how is it corrected?
27. Why does it takes sometimes to see in a dim room when you enter the room from bright sunlight outside.
28. Can we see a rainbow on the moon?
29. Does a beam of light give a spectrum on passing through a hollow prism?
30. What is scattering of light ? Explain with an example .
31. Why planets do not twinkle.
32. What is dispersion? What happens when light is passed through a glass prism.
THREE MARKS QUESTION
33. A person needs a lens of power 4.5 D for correction of her vision.What kind of defect in vision is she suffering from? What is the focal length of the corrective lens?What is the nature of the corrective lens?
34. A person with a myopia eye cannot see objects beyond a distance of 1.5m. What would be the
35. Power of corrective lens? Which type of lens is used?
36. What do you understand by myopia? Write two causes of it?
37. What is hypermetropia? State two causes of hypermetropia with help of ray diagrams to show: The eye defect hypermetropia.
38. What is meant by advance sunrise and delayed sunset ? Draw a labeled diagram to explain these phenomenon.
FIVE MARKS QUESTION
39. Explain myopia and hypermetropia with the help of ray diagrams and show how these defects can be corrected?
40. What is meant by dispersion and recombination? Explain with the help of a diagram? What is a spectrum? Name the various colors of spectrum of white light in proper sequence.
41. what is atmospheric refraction? Use this phenomenon to explain the following natural events. i)Twinkling of stars. ii) advanced sun rise and delayed sun set . Draw a diagrams to illustrate your
ELECTRICITY
ONE MARKS QUESTION
1. Define resistivity of material.
2. What is the power of torch bulb rated at 2.5V and 500mA?
3. Why series arrangement not used for connecting domestic electrical appliances in a circuit?
4. Which has higher resistance – a 50W bulb or a 2.5W bulb and how many times?
5. What is the direction of flow of conventional current?
6. Calculate the amount of charge flowing in a wire if it draws a current of 2A in 10 minutes
7. What happens to resistance of a conductor if area of cross-section is doubled?
8. Which device helps to maintain a potential difference across a conductor?
9. Find the number of electron in 1C of charge.
10. Name the physical quantity whose unit is V/A.
11. Name the device that helps to maintain a potential a potential difference across a conductor.
TWO MARKS QUESTION
12. Draw a circuit diagram having the following components a. Bulb b. A two cell battery c. Ammeter d. A closed key
13. Why are heating elements made of alloys rather than metals?
14. What do we mean when we say that potential difference between two points is 1volt?
15. Why is it not advisable to handle electrical appliances with wet hands?
16. Two electric bulbs marked 100W 220V and 200W 200V have tungsten filament of same length. Which of the two bulbs will have thicker filament?
17. How does the resistance of a wire vary with its area of cross section?
18. Define electric potential? What is its SI unit.
19. State the factor on which at a given temperature the resistance of a cylindrical conductor depends. State the SI unit of resistivity.
20. A circuit has a line of 5 A. How many lamps of rating 40W, 200V can simultaneously run on this line safely.
THREE MARKS QUESTION
21. If three resistors of 6Ω, 9Ω and 21Ω are connected in series to a 12V battery, find
22. What are the advantages of connecting electrical devices in parallel with the battery rather than in series?
23. A geyser is rated 1500W, 250V. This geyser is connected to 250V mains. Calculate - The current drawn The energy consumed in 50hrs,The cost of energy consumed at Rs. 2.20 per kWh.
24. What is the function of an electric fuse? Name the material used for making fuse. In household circuit where is fuse connected?
25. Write one important advantage of using alternative current. How alternating current differ from direct current?
27. 2.4 x 10 20 electrons flow through a circuit in 10 hours. Calculate the magnitude of the current. [Charge on one electron = 1.6 x 10–19 C]. [1.066 x 10 – 3 ]
28. . 50 coulombs of charge is brought from infinity to a given point in an electric field when 62.5 j of work is done. What is the potential at that point? [1.25 V]
29. What is the electric potential at a point in an electric field when 24 j of work is done in moving a charge of 84 C from infinity?[0.285 V]
30. A charge of 75 C is brought from infinity to a given point in an electric field; when the amount of work done is 12.5 j. Calculate the electric potential at that point. [0.166 V]
FIVE MARKS QUESTION
31. Draw diagram showing three resistors R1, R2 and R3 in series. i)Two resistors of resistance 4Ω and 12Ω ii)In parallel iii)In series
32. Calculate the values of effective resistance in each case. (A) What is the function of fuse in an electric circuit? B) How is the SI unit of electric energy related to its commercial unit? (C) What would be the rating of the fuse for an electric kettle which is operated at 220V and consumes 500 W power?
33. a) State Ohms law. Derive the relation and give graphical representation for it. b) An electric oven rated at 500W is connected to a 220V line and used for 2 hours daily. Calculate the cost of electric energy per month at the rate of Rs.5 per KWh
MAGNETIC EFFECT OF CURRENT. ONE MARKS QUESTION
1. What is a solenoid?
2. What is the direction of the magnetic field lines inside a bar magnet?
3. What is the direction of the magnetic field lines outside a bar magnet?
4. State two uses of electromagnet.
5. An electron moving along X – axis in a magnetic field along Y – axis. In which direction will the electron deflected.
6. State Fleming’s left hand rule.
7. Name the sources of direct current.
8. What is the role of split ring in an electric motor?
9. What is an earth wire?
10. What is the surer test of magnetism?
11. What happens if we break a magnet into two pieces?
12. What is the effect of placing an iron core in a solenoid?
TWO MARKS QUESTION
13. What is an electromagnet?
14. What is the difference between a direct current and an alternating current? What is the frequency of AC in India?
15. State the rule to find the direction of magnetic field produced around a current-carrying conductor.
16. Give two points of difference between and electromagnet and permanent magnet.
17. Draw the lines of force indicating field direction of the magnetic field through and around Single loop of wire carrying electric current.
18. A solenoid carrying electric current. What is magnetic field? How is the direction of magnetic field at a point determined ? 19. How do the field lines of the regions of strong field different from those of weak field?
20. Give two advantages of electromagnets.
21. Give four features of domestic electric wiring.
22. Should a copper wire be used as a fuse wire? If not, why?
23. What is the importance of earth wire?
24. Explain the magnetic effects of current with the help of an activity along with a labeled diagram.
THREE MARKS QUESTION
25. What is the role of fuse, used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating?
26. Why does a magnetic compass needle deflect when a bar magnet or a current-carrying loop is brought near it. Draw a schematic diagram of domestic wiring system and write its main features.
27. Draw a labelled diagram to show how an electromagnet is made.
28. What is the purpose of the soft iron core in making an electromagnet?
29. Write two differences between AC and DC current and draw diagram also.
30. What is the solenoid ? Draw the field lines of the magnetic field produced on passing current through and around a current carrying solenoid.
FIVE MARKS QUESTION
31. Write principle of the electric generator. Explain construction and working of a generator. Draw labelled diagram of the electric generator.
32. Describe any five safety measure that should be taken while dealing with electric appliance connected in the domestic electric circuit.
SOURCE OF ENERGY
ONE MARKS QUESTION
1. Thermal power plants are set up near coal or oil fields. Give reason
2. Name the component of sunlight, exposure to which may cause skin cancer.
3. Flowing water possess which type of energy.
4. Name one place in India where wind energy power station is installed.
5. What is a solar panel?
6. What type of energy transformation takes place during winding of spring of a clock?
7. Name the process that produces a large amount of energy in the sun.
8. Why is biogas called a clean fuel?
9. Name the materials used for making solar cells.
TWO MARKS QUESTION
10. List two advantages and disadvantages each for using wind as a source of energy.
11. Write two differences between renewable and non – renewable sources of energy.
12. What is the principle of solar cooker? Name two types of solar cooker.
13. Name any two types of harmful nuclear radiations emitted during nuclear fission.
14. What is thermal power plant? Where it is preferably situated?
15. What is the use of black painted surface in solar heating devises.
16. Why are bio gas plants considered to be boon to the farmers? Give reason.
17. Hydroelectricity generated at a dam may be considered another form of solar energy. Why?
18. Why is charcoal considered to be a better fuel than wood?
19. Why a solar cooker cannot be used for frying or making chapattis?
20. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
21. Fire wood is our conventional fuel. List any four reasons for replacing it with the alternate sources of energy.
THREE MARKS QUESTION
22. What is a solarcell panel? List two advantages and disadvantages each of using Solar cells for producing electricity.
23. What is the principle of solar cooker? Give two limitations and two advantages of solar 30Name the fuel for hydropower plant. Mention two advantages and disadvantages of producing electricity at the hydropower plant.
24. Explain why: a. It is difficult to burn a piece of fresh wood from a tree. b. Pouring dry sand over the fire extinguishes it. c. It is difficult to use hydrogen as a source of energy.
25. What are the different types of energies obtained from the sea? Explain.
26. How is the slurry left over after the generation of biogas in biogas plant used?
27. In parabolic reflector type coolers, even temperature up to 1800C- 2000C can be attained. How?
28. Modern chulahs are more efficient than traditional chulahs. Why?
29. How is hydro energy converted into electrical energy?
30. Explain, why only a part of the solar energy that strikes the upper regions of atmosphere reaches the surface of the earth?
FIVE MARKS QUESTION
31. Describe the design and function of each part of a solar cooker with the help of a neat labelled diagram.

32. What is a principle of Biogas?Explain it working in brief.Draw a labelled diagram of biogas plant.

## 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
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
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.

## Sunday, 9 July 2017

### CBSE CLASS 11 PHYSICS UNITS AND MEASUREMENT WORKSHEET

WORKSHEET#1 UNITS AND MESUREMENT
1. If the unit of force is 100N, unit of length is 10m and unit of time is 100s. What is the unit of Mass
in this system of units? 105kg.
2. Using dimensions convert (a) 1 newton into dynes (b) 1 erg into joules.
3. The magnitude of force experienced by an object moving with speed v is given by F = kv2. Find
Dimensions of k.
4. Give limitations of dimensional analysis.
5. For Determination of g using simple pendulum, measurements of length and time period are
required. Error in the measurement of which quantity will have a larger effect on the value of g           thus obtained. What is done to minimise error?
6. Describe the Parallax Method for the determination of the distance of a nearby star from the earth.
7. Define the following units :(i) Lightyear (ii) Parsec(iii) Astronomical unit (Au)
8. Distinguish between the terms precision and accuracy of a measurement.
9. Explain
(i) absolute error (ii) mean absolute error(iii) relative error (iv) percentage error
(v) random error
10. Determine the number of light years in one metre. 1.057 × 10-16 Iy
11. The sides of a rectangle are (10..5 ± 0.2) cm and (5.2 ± 0.1) cm. Calculate  its perimeter with error
limits. (31.4 ± 0.6) cm.
12. The mass of a box measured by a grocer’s balance is 2.3 kg. Two gold
pieces 20.15 g and 20.17 g are added to the box.
(i) What is the total mass of the box? 2.3 kg
(ii) The difference in masses of the pieces to correct significant figures. 0.02 g
13. 5.74 g of a substance occupies 1.2 cm3. Express its density to correct significant figures. 4.8 g/cm3.
14. If displacement of a body s = (200 ± 5) m and time taken by it t = (20 +0.2) s, then
find the percentage error in the calculation of velocity. 3.5%
15. If the error in the measurement of mass of a body be 3% and in the measurement of velocity be
2%.What will be the maximum possible error in the calculation of kinetic energy. 7%
16. The length of a rod as measured in an experiment was found to be 2.48m, 2.46m, 2.49m, 2.50m and 2.48m. Find the average length, absolute error and percentage error. Express the result with error
limit. (2.48 ± 0.01)m (2.48m ± 0.40%)
17. A physical quantity is measured as Q = (2.1 ± 0.5) units. Calculate thepercentage error in (1) Q2   (2) 2Q. 48% and 24%
18. When the planet Jupiter is at a distance of 824.7 million km from the earth, its angular diameter is
measured to be 35.72¢¢ of arc. Calculate diameter  of Jupiter. 1.4287 × 105 km
19. A laser light beamed at the moon takes 2.56s and to return after reflection at the moon.s surface.
What will be the radius of lunar orbit. 3.84 × 108 m.
20. Convert
(i) 3 m/s.-2 to km/ h-.2            3.9 × 104 km h-.2
(ii) G = 6.67 × 10.-11 N m2 kg-2 to cm3 g-1 s-2 6.67 × 10-8 g-1 cm3 s-2.
21. A calorie is a unit of heat or energy and it equals 4.2 J where 1J = 1 kg  m2s-2. Suppose we employ a
system of units in which unit of mass is a kg,  unit of length is b m, unit of time gs. What will be
magnitude of calorie in terms of this  new system. n2 = 4.2 a-1 b-2 g2

22. The escape velocity v of a body depends on.
(i) the acceleration due to gravity g of the planet,
(ii) the radius R of the planet. Establish dimensionally the relation for the escape
velocity

23. The frequency of vibration of a string depends of on, (i) tension in the string (ii) mass
per unit length of string, (iii) vibrating length of the string. Establish dimensionally the
relation for frequency.

24. One mole of an ideal gas at STP occupies 22.4 L. What is the ratio of
molar volume to atomic volume of a mole of hydrogen? Why is the ratio
so large. Take radius of hydrogen molecule to be 1ºA.  104 This ratio is large    because actual size of gas molecule is negligible incomparison to the inter molecular separation.

25. Derive an expression for the centripetal force F acting on a particle of
mass m moving with velocity v in a circle of radius r.

26. The error in the measurement of radius of a sphere is 2%. What would be
the error in :
(a) Volume of sphere

(b) Surface area of sphere.