# CBSE CLASS 12 PHYSICS SAMPLE PAPER 2018 IN PDF

## Class 12 Physics Practice Paper 2018

General Instructions:
1. All questions are compulsory.There are 26 questions in all.
2. This question paper has 5 sections.
3. 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.
4. There is no overall choice,however internal choice has been provided in one question of three marks and all questions of five marks.

Section - A

1. A 500 µc charge is at the centre of a square of side 10 cm.Find the work done in moving a charge of 10 µc between two diagonally opposite points on the square.
2. A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index.what would be the focal length of the lens in this medium?
3. The output of a two input AND gate is  fed to a NOT gate. Draw the logic circuit of this combination of Gates and name it.
4. Show the variation of photo current with collector plate potential for different intensity by same frequency of incident radiation.
5. Give an example of a material is for which temperature coefficient of resistivity is-
(i)   Positive              (ii)  Negative
Section - B

6. Distinguish between EMF(E)  and terminal voltage(V)  of a cell having internal resistance ‘r’ .Draw a plot showing the variation of terminal voltage versus current drawn from the cell. Using this plot, how does one determine the internal resistance of the cell?
7.The value of ground state energy of hydrogen atom is -13.6 electron volt.
(i)  Find the energy required to move an electron from the ground state to the first excited state of the atom.
(ii)  Determine the kinetic energy in the first excited state of the atom.
8. A nucleus  10Ne23  undergoes beta decay and becomes  11Na23. Calculate the maximum kinetic energy of electrons emitted assuming that beta particle and Antineutrino carry negligible kinetic energy.
Mass of 10Ne23 =  22.99 4466  u
Mass of 11Na23 =  22.989 770 u
1 u = 931 .5 Mev/c2
9. A Ray of light passing through an equilateral triangular glass prism from air undergoes minimum deviation when angle of incidence is 3/4th  of the angle of prism.  Calculate the speed of light in the prism.
10. The input waveforms ‘A’ and ‘B’ and the output waveform ‘Y’ of a gate are shown below. Name the gate it represents, write its truth table and draw the logic symbol of this gate.

Section - C

11. The potential difference across a resistor ’r’  carrying current ‘I’  is ‘Ir’ .
(i) Now if the potential difference across ‘r’  is measured using a voltmeter of resistance ‘R’ , show that the reading of voltmeter is less than the true value.
(ii) Find the percentage error in measuring the potential difference by a voltmeter.
(iii) At what value of R, does the voltmeter measures the true  potential difference?
12. The magnetic field through a single loop of wire 12 cm in radius and 8.5 ohm resistance, changes with time as shown in figure. The magnetic field is perpendicular to the plane of the loop. Plot induced current as a function of time.

13. Write three characteristic features in Photoelectric effect which cannot be explained on the basis of wave theory of light.
14. Right Maxwell's modification of Ampere's circuital law. Show that in the process of charging a capacitor,  the current produced with in the plates of the capacitor is,
I = єo(dφe/dt)
15. Explain the need of modulation.
16.(a) State Bohr’s quantization condition for defining stationary orbits.  How does de -Broglie hypothesis explain the stationary orbits?
(b) Find relation between three wavelength λ1, λ2 and λ3 from the energy level diagram.

17.(i) Write a basic nuclear process involved in the emission of β+ in a symbolic form, by a radioactive nucleus.
(ii)  in the reactions given below-
6C11yBz + x + ʋ
6C12 + 6C12  aNe20 +  bHec
Find the values of x, y, z, a, b, and c.
18.(i) Explain with the help of a diagram, the formation of depletion region and barrier potential in a p-n Junction.
(ii) Draw the circuit diagram of Full wave Rectifier and explain its working.
19. (i) State the advantages of Reflecting type telescope over Refracting type.
(ii) Write the expression for resolving power of a compound microscope. How can the resolving power of a microscope be increased.
20. (i) Describe the working of photodiode by drawing its circuit diagram.
(ii) Draw the characteristics of a photodiode for different illumination intensities.
21. Deduce the expression for the torque acting on a dipole placed in a uniform electric field.
OR
Deduce the expression for potential energy of the dipole. Find out the work done in rotating it from the position of unsstable equilibrium to the stable equilibrium.
22.Two identical coils P and Q each of radius R are lying in perpendicular planes such that they have a common centre. Find the magnitude and direction of magnetic field at the common centre of two coils, if they carry currents equal to I and √3I  respectively.

Section - D

23. Gautam went for a vacation to the village where his grandmother lived his grandmother took him to watch Nautanki one evening. They noticed a black box connected to the mic line nearby. Goutam's grandmother did not know what that box was. When she ask this question to Gautam he explained to her that it was an amplifier.
(i) Which values were displayed by grandmother?  Which values are displayed by Gautam.
(ii)What is the function of an amplifier?
(iii) Which basic electronic device is used in the amplifier?
Section - E

24. (i) State the essential conditions for diffraction of light.
(ii) Explain diffraction of light due to a narrow single slit and the formation of pattern of fringes on the screen.
(iii) Find the relation for width of Central Maxima in terms of wavelength λ , width of slit a and separation between the slit and screen D.
(iv) If width of Slit is made double, how does it affect the size and intensity of Central band.
OR
(i) Draw a labelled diagram of astronomical telescope in normal adjustment.
(ii) Derive expression for magnifying power of Astronomical Telescope when image is formed at least distance of distinct vision.

25. A 2 µF capacitor, 100 ohm resistor and 8 H  inductor are connected in series with an AC  source.
(i) What should be the frequency of the source such that the current drawn in the circuit is maximum? What is this frequency called?
(ii) If the peak value of EMF of source is 200 volt, find the maximum current.
(iii) Draw a graph showing variation of amplitude of circuit current with changing frequency of applied voltage in a series LRC circuit for two different values of resistance R1 and R2( R1> R2).
(iv) Define the term ‘sharpness of resonance’. Under what condition, does a circuit become more selective.
OR
(i) With the help of a neat labelled diagram, explain the principle and working of a moving coil galvanometer.
(ii) What is the function of uniform radial field and how is it produced?
(iii) Define current sensitivity of a galvanometer. How is current sensitivity increased?

26. With the help of a circuit diagram explain the working of CE transistor as an amplifier.
OR
(a) Show that in a parallel plate capacitor, if the medium between the plates of a capacitor is filled with an insulating substance of dielectric constant k, its capacitance increases.
(b) Deduce the expression for the energy stored in a capacitor of capacitance C with charge Q.