[Sashwat]

Can you please give me the Central Board of Secondary Education guess papers of Physics as it is very urgent for me?

As you want to get the Central Board of Secondary Education guess papers of Physics so here is the information of the same for you:

Q.1 In the given figure , bar magnet is quickly moved towards a conducting loop having a capacitor . Predict the polarity of the plates A and B of the capacitor.

Q.2 Where on the surface of earth is the vertical component of earth’s magnetic field zero ?

Q.3 What is the meaning of the term attenuation in communication system ?

Q.4 A biconvex lens has a focal length 2/3 times the radius of curvature of either surface . Calculate the refractive index of lens material.

Q.5 A charge q is placed at the centre of a cube of side l. What is the electric flux passing through each face of the cube ?

Q.6 Two semiconductor materials A and B shown in the given figure, are made by doping germanium crystal with arsenic and indium respectively. The two are joined end connected to a battery as shown. (i) Will the junction be forward biased or reverse biased ?
(ii) Sketch a V-I graph for this arrangement.


Q.7 What is space wave communication ? Write the range of frequencies suitable for space wave communication.

Q.8 The instantaneous current and voltage of an AC circuit are given by, I=10 sin314t A and V=50 sin 314t volt. What is the power dissipation in the circuit ?

Q.9 Laser light of wavelength 630 nm, incident on a pair of slits produces an interference pattern in which the bright fringes are separated by 7.2 mm. Calculate the wavelength of another source of laser light which produces interference fringes separated by 8.1 mm using same pair of slits.

Q.10) Net capacitance of three identical capacitors in series is 1 µF. What will be their net capacitance if connected in parallel ? Find the ratio of energy stored in the two configurations if they are both connected to the same source.
OR
Two identical metallic spherical shells A and B having charges +4Q and -10Q are kept a certain distance apart. A third identical uncharged sphere C is first placed in contact with sphere A and then with sphere B, then spheres A and B are brought in contact and then separated . Find the charge on the spheres A and B.

Q.11 Write Einstein’s photoelectric equation. State clearly the three salient features observed in photoelectric effect, which can be explained on the basis of above equation.

Q.12 Conductor of length l is connected to a DC source of potential V. If the length of the conductor is tripled by gradually stretching it, keeping V constant , how will
(i) drift speed of electrons and (ii) the resistance of the conductor be affected ? Justify your answer.

Q.13 Figure shows two identical capacitors C1 and C2 each of 1.5 µF capacitance, connected to a battery of 2 V. Initially switch S is closed. After some time S is left open and dielectric slabs of dielectric constant K=2 are inserted to fill completely the space between the plates of the two capacitors. How will the (a) charge and (b) potential difference between the plates of the capacitors be affected after the slabs are inserted ?



Q.14 A cyclotron when being used to accelerate positive ions ( Mass= 6.7 x 10-27 kg , charge =3.2 x 10-19 C) has a magnetic field of π/2 T. What must be the value of the frequency of the applied alternating electric field to be used in it ?

Q. 15 (a) For what kinetic energy of a neutron will the associated de-Broglie wavelength be 1.40 x 10-10 m ? (b) Also find the de-Broglie wavelength of a neutron, in thermal equilibrium with matter , having an average kinetic energy of kT at 300 K.
Q.16 Draw the (a) symbol and (b) the reverse I-V characteristics of a Zener diode . Explain briefly , which property of the characteristics enables us to use Zener as voltage regulator.

Q.17 Determine the current in each branch of the network shown in figure.


Q. 18 The energy of the electron in the ground state of hydrogen is -13.6 eV. Calculate the energy of the photon that would be emitted if the electron were to make a transition corresponding to the emission of the first line of the (a) Lyman series (b) Balmer series of the hydrogen spectrum.

Q 19 Using Huygen’s geometrical construction of wavefronts, show how a plane wave gets reflected by a plane, reflecting surface. Hence , verify laws of reflection.

Q.20 An electron moves around the nucleus in a hydrogen atom of radius 0.51 A0 with a velocity of 2 x 105 m/s. Calculate the following
(a) The equivalent current due to orbital motion of electron.
(b) The magnetic field produced at the centre of the nucleus.
(c) The magnetic moment associated with the electron.

Q.21 A compound microscope uses an objective lens of focal lengths 4 cm and eyepiece lens of focal length 10 cm. An object is placed at 6 cm from the objective lens. Calculate the magnifying power of the compound microscope. Also calculate the length of the microscope.

Q.22 Draw a plot of binding energy per nucleon (BE/A) versus mass number (A) for a large number of nuclei lying between 2 OR
Draw the graph to show variation of binding energy per nucleon with mass number of different atomic nuclei . Calculate binding energy/nucleon of 20Ca40 nucleus.
Given , mass of 20Ca40= 39.962589 u, mass of proton=1.007825 u, mass of neutron=1.008665u and 1 u= 931 MeV/c2

Q.23 Write briefly any two factors which demonstrate the need for modulating a signal. Draw a suitable diagram to show amplitude modulation using a sinusoidal signal as the modulating signal.

Q24. A parallel plate capacitor is charged by a battery. After sometime , the battery is disconnected and a dielectric slab of dielectric constant K is inserted between the plates. How would
• The capacitances (b) the electric field between the plates and
(c)the energy stored in the capacitor , be affected ? Justify your answer .

Q25. Write any four characteristics of electromagnetic waves. Give two uses each of
• Radiowaves (ii) microwaves
•
Q26. On a field Ram and Shyam were playing football. Suddenly , a player kicked out the ball outside the field and the ball reached an electric power substation. One of the players was planning to go and bring back the ball to the field but, Ram and Shyam stopped him saying that it is dangerous to go to the substation as warmed up body can be caught by the strong magnetic field, which is created by high voltage current in conductions of the switchyard and that may result in death.
• Ram and Shyam are the student of class 12. Consider yourself as this friend and give your opinion about them.
• There is a conductor of length L in a magnetic field B, current i flows through the conductor. Calculate the force acting on the conductor ( B= constant)
Here magnetic field B is also produced by the current flowing in the conductor other than the considered conductor.
Q27. A sinusoidal voltage of peak value 283 V and frequency 50 Hz is applied to a series L-C-R circuit in which R=3 Ω, L=25.48 mH and C=796 µF. Find (a) the impedance of the circuit (b) the phase difference between the voltage across the source and the current (c) the power dissipated in the circuit and (d) the power factor.
OR
• With the help of a labeled diagram, describe briefly the underlying principle and working of a step-up transformer.
• Write any two sources of energy-loss in a transformer.
• A step-up transformer converts a low input-voltage into a high output-voltage. Does it violate law of conservation of energy ? Explain.
•
Q28. (a) Draw the circuit arrangement or studying the input and output characteristics of an n-p-n transistor in CE configuration. With the help of these characteristics define
(i) input resistance (ii) current amplification factor
(b) Describe briefly with the help of a circuit diagram how an n-p-n transistor is used to produced self-sustained oscillations.
OR
(a) Draw the circuit diagram of a p-n junction diode in
(i) forward bias (ii) reverse bias
How are the circuits to study the V-I characteristics of a silicon diode ? Show the typical V-I characteristics.
(b) What is a Light Emitting Diode (LED) ? Mention two important advantage of LEDs over conventional lamps.

Q29. (a) Obtain lens maker’s formula using the expression
Here the ray of light propagating from a rare medium of refractive index
(n1) to a denser medium of refractive index (n2) is incident on the convex side of spherical refracting surface of radius of curvature R.
(b)Draw a ray diagram to show that image formation by a concave mirror when the object is kept between its focus and the pole. Using this diagram, derive the magnification formula for the image formed.
OR
With the help of ray diagram, explain the formation of image in an astronomical telescope
for a distant object. Derive an expression for its magnifying power when the final image is
formed at the least distance of distinct vision.

General Instructions:
• All questions are compulsory.
• 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 questions of five marks. You have to attempt only one the choices in such questions.
• Question numbers 1 to 8 are very short answer type questions, carrying one mark each.
• Questions numbers 9 to 16 are short answer type questions carrying two marks each.
• Question numbers 17 to 25 are also short answer type questions, carrying 3 marks each.
• Question numbers 26 value based type question, carrying four marks each.
• Question numbers 27 to 29 are long answer type questions, carrying five marks each.
• Use of calculators is not permitted. However, you may use log tables, if necessary.
You may use the following physical constants wherever necessary.
c = 3 x 108 ms-1
h = 6.6 x 10-34 Js
e = 1.6 x 10-19C
µo = 4π x 10-7 TmA-1
1/4πεo = 9 x 109 N m2C-2
Avogadro number NA = 6.023 x 1023 mol-1
Mass of the neutron = 1.675 x 10-27 kg
Boltzmann constant, k = 1.38 x 1023 J K-1

1. An electron beam projected along +X axis, experiences a force due to a magnetic field along the
+ Y-axis. What is the direction of the magnetic field?
2. The instantaneous current from an ac source is I = 6 sin 314t. What is the rms value of the current?
3. A bulb connected in series with a solenoid is lit by ac source. If a soft iron core is introduced in the solenoid, will the bulb glow brighter?
4. Which part of the electromagnetic spectrum is used in operating RADAR? Give its wavelength range.
5. Two thin lenses + 6D and -2D are in contact. What is the focal length of the combination?
6. The ionization potential of hydrogen is 13.6 V. calculate the energy of its first excited state.
7. How does the collector current change in a junction transistor, if the base region has larger width?
8. How does the conductivity change of a semiconductor with increase of temperature?
9. Define the term temperature coefficient of resistivity. Draw a graph showing the variation of resistivity with temperature for copper.
10. S1 and S2 are two hollow concentric sphere enclosing charges Q and 2Q respectively as shown in fig.
(a)What is the ratio of electric flux through S1 & S2?
(b)How will the electric flux through the sphere change, if a medium of dielectric constant 5 is introduced in the space inside S1 in place of air?

11. Two cells E1 and E2 in the given circuit diagram have an emf of 4V and 8V and internal resistance 0.5 and 1.0 respectively. Calculate the current flowing through the resistance of 3.

12. How will a dia & ferro magnetic material behave when kept in a non-uniform external field? Give two examples each.
13. A double concave lens of glass of RI 1.6 has radii of curvature of 40cm, 60cm. Calculate its focal length. Also find the focal length of the lens if the lens is immersed in a liquid of RI 1.3.
14. Show that the de-Broglie wavelength  of electrons of energy E is given by the relation
 =
15. If the frequency of light on metal surface is doubled, will the kinetic energy of photoelectrons be doubled. Explain ?
16. Define half life. Derive the relation between half life and decay constant.
17. Define electric dipole. Derive an expression for eclectic potential on the axis of dipole.
18. State Guass’s theorem in electrostatics. Derive an expression for electric field intensity produced by charged thin sheet using this theorem.
19. Write the principle of potentiometer. Explain with diagram how will you measure internal resistance of a cell using potentiometer.
20. Derive a relation between root mean square value and peak value of alternating current.
21. Three rays of light red (R), green (G) and blue (B) are incident on the face AB of a right angled prism ABC. The refractive indices of the material of the prism for red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. Trace the path of the rays through the prism. How will the situation change if these rays were incident normally on one of the faces of an equilateral prism?
22. State radioactive disintegration law and deduce the relation N = N0e-λt where symbols have their usual meaning.
23. Define mutual inductance. Derive an expression for mutual inductance of two long co-axial solenoid of sane length wound over the other.
24. Draw a labeled ray diagram to show the image formation by an astronomical telescope when final image is forms at least distance of distinct vision. Derive an expression for its magnifying power.
25. (a) With the help of block diagram, briefly explain the function of a receiver for detection of amplitude modulated wave.
(b)A radio can tune two any stations in 7.5MHz to 12MHz band. What is corresponding wavelength band.
26. Monica had come from Singapore on a holiday to her grandmother’s place. She had heard a lot about Tirupathi temple and so she went to Tirupathi with her grandmother. She walked through a metal detector and heard a beep sound as she walked through it. When she went back to Singapore she asked her father about the metal detector and its working. Her father explained the working in detail and also the need for installing metal detectors in places where
people visited in huge numbers.
a) Name the components present in the detector .
b) What is the phenomenon involved?
c) What value can be attached with this?
27. Draw a graph to show the variation of the angle of deviation with that of the angle of incidence for a monochromatic ray of light passing through a glass prism of refracting angle A and deduce the relation for its refractive index in terms of refracting angle and minimum deviation. Also explain Angular dispersion and Dispersive power.
OR
Define the term wave front. Draw the wave front and corresponding rays in the case of a (i) diverging spherical wave, (ii) plane wave.
Using Huygen’s postulates explain the refraction of a plane wave front at a plane surface and hence verify Snell’s law.

28. Draw a circuit diagram to study the input and output characteristic of an n-p-n transistor in common emitter mode. Explain these characteristics graphically.
OR
(a)Explain the use of Zener diode as voltage regulator.
(b)The output of an OR gate is connected to both the inputs of a NAND gate. Draw the logic circuit of this combination of gates and write its truth table.
29. (a) Using Biot- Savart’s law derive an expression for magnetic field intensity on the axis of a circular coil carrying current.
(b) To small circular loops each of radius R marked 1 and 2 carrying equal currents are placed with the geometrical axis perpendicular to each other as shown in fig. find the magnitude and direction of the net magnetic field produced at the point O.

OR
State Ampere circuital law, A long solenoid with closely wound turns has n turns per unit length. A steady current I flows through this solenoid. Use ampere circuital law, how to obtain an expression for magnetic field at a point on its axis and close to its mid point.

Contact Details:
Central Board of Secondary Education
Community Centre,
Preet Vihar Metro Railway Station,
Shiksha Kendra,Building No.2,
Acharya Nag Raj Marg, Block D,
Preet Vihar,
New Delhi,
Delhi 110092 ‎
011 2202 3737
India

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[Nilesh]

Here, I am giving you sample paper of the Central Board of Secondary Education class 12th physics. it will fruitful for you.

What is Bohr magnetron?
Suggest two methods by which method the range of transmission by a TV tower can be increased.
A carbon resistor of 47 kΩ is to be marked with rings of different colours for its identification.
Write the sequence of colours of rings.
The energy of the hydrogen atom in its ground state is 13.6 eV. Calculate the energy of the atom in the second excited state.
What is the threshold frequency of a photon for photoelectric emission from a metal of work function 0.1 eV?
Two lenses of power +4 and 2 dioptres respectively are placed 10 cm apart. What is focal length and power of the combination?
The magnetic flux threading a coil changes from 12x10 -3 Wb to 6x10 -3 Wb in 0.01 s. Calculate the induced emf.

CBSE Class 12th physics sample paper