CBSE Question Paper 2012 Class 12 Physics

General Instructions:

• All questions are compulsory.
• There are 30 questions in total. Question Nos.1 to 8 are very short answer type questions and carry one mark each.
• Question Nos.9 to 18 carry two marks each, Question Nos.19 to 27 carry three marks each and Question Nos.28 to 30 carry five marks each.
• 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 three questions of five marks each. You have to attempt only one of the choices in such questions.
• Use of calculators is not permitted. However, you may use log tables if necessary.
• You may use the following values of physical constants wherever necessary:
  

1. Why must electrostatic field be normal to the surface at every point of a charged conductor?

2. Under what condition does a biconvex lens of glass having a certain refractive index act as a plane glass sheet when immersed in a liquid?

3.State de-Broglie hypothesis.

4. Name the physical quantity which remains same for microwaves of wavelength 1 mm and UV radiations of 1600  in vacuum.

5. When electrons drift in a metal from lower to higher potential, does it mean that all the free electrons of the metal are moving in the same direction?

6. Predict the direction of induced current in a metal ring when the ring is moved towards a straight conductor with constant speed v. The conductor is carrying current I in the direction shown in the figure.

7. The horizontal component of the earth’s magnetic field at a place is B and angle of dipis60°. What is the value of vertical component of earth’s magnetic field at equator?

8. Show on a graph, the variation of resistivity with temperature for a typical semiconductor.

9. Draw a plot showing the variation of (i) electric field (E) and (ii) electric potential

(V) with distance r due to a point charge Q.

10. Derive the expression for the self-inductance of a long solenoid of cross sectional area A and length l, having n turns per unit length. ·

11. A ray of light, incident on an equilateral glass prism (µ_g= ) moves parallel to the base line of the prism inside it. Find the angle of incidence for this ray.

12. The current in the forward bias is known to be more(-mA) than the current in the reverse bias(-µA). What is the reason, then, to operate the photo diode in reverse bias?

13. Distinguish between ‘Analog and Digital signals’.

OR

Mention the function of any two of the following used in communication system: (i)Transducer

(ii) Repeater

(iii) Transmitter

(iv)Bandpass Filter

14. The susceptibility of a magnetic material is 2.6 x 10^-5. Identify the type of magnetic material and state its two properties.

15. A cell of emf E and internal resistance is connected to two external resistances R₁ and R₂ and a perfect ammeter. The current in the circuit is measured in four different situations:

(i) without any external resistance in the circuit

(ii) with resistanceR1only

(iii) with R₁and R₂ in series combination

(iv) with R₁and R₂ in parallel combination

The currents measured in the four cases are 0.42 A, 1.05A, 1.4 A and 4.2 A, but not necessarily in that order. Identify the currents corresponding to the four cases Mentioned above.

16. Two identical circular loops, P and Q, each of radius r and carrying I and 2I respectively are lying in parallel planes such that they have a common axis. The direction of current in both the loops is clockwise as seen from O which is equidistant from the both loops. Find the magnitude of the net magnetic field at point 0.

17. A metallic rod of ‘L’ length is rotated with angular frequency of ‘ ‘ with one end hinged at the centre and the other end at the circumference of a circular metallic ring of radius L, about an axis passing through the centre and perpendicular to the plane of the ring. A constant and uniform magnetic field B parallel to the axis is present everywhere. Deduce the expression for the emf between the centre and the metallic ring.

18. When an ideal capacitor is charged by a de battery, no current flows. However, when an ac source is used, the current flows continuously. How does one explain this, based on the concept of displacement current?

19. In the figure a long uniform potentiometer wire AB is having a constant potential gradient along its length. The null points for the primary cells of emf  connected in the manner shown are obtained at a distance of 120cm and 300cm from the end A. Find (i) E /E₂and (ii) position of null point for the cell E1.

How is the sensitivity of a potentiometer increased?

OR

Using Kirchhoff’s rules determine the value of unknown resistance R in the circuit so that no current flows through 4 resistance. Also find the potential difference between A and D.

20. A series LCR circuit with L = 4.0 H, C= 100 µF and R = 60 n is connected to a variable frequency 240 V source as shown in.

Calculate:

(i) the angular frequency of the source which derives the circuit at resonance;

(ii) the current at the resonating frequency;

(iii) the rms potential drop across the inductor at resonance.

21. (a) Why are coherent sources necessary to produce a sustained interference pattern?

(b) In Young’s double slit experiment using mono-chromatic light of wavelength , the intensity of light at a point on the screen where path difference is , is K units. Find out the intensity of light at a point where path difference is .

22. A rectangular loop of wire of size 2 cm x5cm carries a steady current of 1 A. A straight long wire carrying 4 A current is kept near the loop as shown in the figure. If the loop and the wire are coplanar, find (i) the torque acting on the loop and (ii) the magnitude and direction of the force on the loop due to the current carrying wire.

23. Write Einstein’s photoelectric equation. State clearly how this equation is obtained using the photon picture of electromagnetic radiation.

Write the three salient features observed in photoelectric effect which can be explained using this equation

24. (a) Using Bohr’s second postulate of quantization of orbital angular momentum show that the circumference of the electron in the n^th orbital state in hydrogen atom is n times the de Broglie wavelength associated with it.

(b) The electron in hydrogen atom is initially in the third excited state. What is the maximum number of spectral lines which can be emitted when it finally moves to the ground state?

25. UseHuygens’sprincipletoexplaintheformationofdiffractionpatternduetoa single slit illuminated by a monochromatic source of light.

When the width of the slit is made double the original width, how would this affect the size and intensity of the central diffraction band?

26. (i)What characteristic property of nuclear force explains the constancy of binding energy per nucleon(BE/A) in the range of mass number ‘A’ lying 30<A< 170?

(ii) Show that the density of nucleus over a wide range of nuclei is constant Independent of mass number A.

27. Name the three different modes of propagation of electromagnetic waves. Explain, using a proper diagram the mode of propagation used in the frequency range above 40MHz.

28. Define magnifying power of a telescope. Write its expression.

A small telescope has an objective lens of focallength150cm and an eye piece of focallength5 cm. If this telescope is used to view a 100m high tower 3 km away, find the height of the final image when it is formed 25 cm away from the eye piece.

OR

How is the working of a telescope different from that of a microscope?

The focal lengths of the objective and eyepiece of a microscope are1.25cm and 5 cm respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of 30 in normal adjustment.

29. Draw a simple circuit of a CE transistor amplifier. Explain its working. Show that the voltage gain, Ay, of the amplifier is given by  where  is the current gain, R_L is the load resistance and r_i is the input resistance of the transistor. What is the significance of the negative sign in the expression for the voltage gain?

OR

(a) Draw the circuit diagram of a full wave rectifier using p-n junction diode. Explain its working and show the output, input waveforms.

(b) Show the output waveforms (Y) for the following inputs A and B of

(i) OR gate (ii) NAND gate

30. Explain the principle of a device that can build up high voltages of the order of a few million volts.

Draw a schematic diagram and explain the working of this device.

Is there any restriction on the upper limit of the high voltages set up in this machine? Explain.

OR

(a) Define electric flux. Write its S.I. units.

(b) Using Gauss’s law, prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance from it.

(c) How is the field directed if (i) the sheet is positively charged,(ii) negatively charged?

Last Year Question Paper Class 12  Physics 2012

Download class 12 Physics question paper with solution from best CBSE App the myCBSEguide. CBSE class 12 Physics question paper 2012 in PDF format with solution will help you to understand the latest question paper pattern and marking scheme of the CBSE board examination. You will get to know the difficulty level of the question paper.

Previous Year Question Paper for class 12 in PDF

CBSE question papers 2018, 2017, 2016, 2015, 2014, 2013, 2012, 2011, 2010, 209, 2008, 2007, 2006, 2005 and so on for all the subjects are available under this download link. Practicing real question paper certainly helps students to get confidence and improve performance in weak areas.

• Physics
• Chemistry
• Mathematics
• Biology
• Accountancy
• Business Studies
• Economics
• History
• Geography
• Political Science
• Physical Education
• Computer Science
• Informatics Practices
• English Core
• Hindi Core
• Hindi Elective
• Other Subjects

To download CBSE Question Paper class 12 Accountancy, Chemistry, Physics, History, Political Science, Economics, Geography, Computer Science, Home Science, Accountancy, Business Studies and Home Science; do check myCBSEguide app or website. myCBSEguide provides sample papers with solution, test papers for chapter-wise practice, NCERT solutions, NCERT Exemplar solutions, quick revision notes for ready reference, CBSE guess papers and CBSE important question papers. Sample Paper all are made available through the best app for CBSE students and myCBSEguide website.