06 “Press forward. Do not stop, do not linger in yourjourney, but strive for the mark set before you.”

– George Whitefield MOCK PAPERS

c = 3 x 108 m/sh = 6.63 x 10-34 Jse = 1.6 x 10-19 C

o = 4 x 10-7 T m A-1

0 = 8.854 x 10-12 C2 N-1 m-2

1 = 9 x 109 N m2 C-2

4 0

me = 9.1 x 10-31 kgmass of neutron = 1.675 x 10-27 kgmass of proton = 1.673 x 10-27 kgAvogadro's number = 6.023 x 1023 per gram moleboltzmann constant = 1.38 x 10-23 JK-1

SECTION-AQ.1 Explain why resistivity of metal increasesand that of semiconductor decreases with risein temperature

Q.2 No two electric lines of force can intersecteach other. why?

Q.3 Write the following radiations in thedescending order of frequencies: red light, x-rays, micro waves and radio waves

ORThe charging current for a capacitor is 0.5A.What is the displacement current across itsplates.

Q.4 The refractive index of material of a con-vex lens is n1. It is immersed in a medium ofrefractive index n2. A parallel beam of light isincident on the lens. Trace the path of emer-gent ray when n2>n1.

Q.5 An alpha particle and proton are accelerat-ed through same potential difference.Calculate the ratio of their linear momenta?

ORCalculate the energy associated in ev with aphotan of wavelength 4000A0?

SECTION-BQ.6 In a potentiometer arrangement a cell ofemf 1.25v gives a balancing point at 35.0cmlength of the wire. If the cell is replaced by

another cell balancing length shifts to 63.0cm.Find the emf of second cell.

ORThree identical cells each of emf 2v andunknown internal resistance are connected inparallel. This combination is connected to a 50ohm resistor.If the terminal voltage across thecell is 1.5v. What is the internal resistance ofeach cell.

Q.7 Determine the equivalent resistance ofnetworks shown in the figures

ORA storage battery of emf 8.0V and internalresistance 0.5ohms is being charged by a 120Vdc supply using a series resistor of 15.5ohms.What is the terminal voltage of the batteryduring charging? What is the purpose of hav-ing series resistor in the charging circuit.

Q.8 If a series LCR circuit connected to an acsource of variable frequency and voltage V=Vm sin wt, Draw a plot showing the variationof current I with angular frequency? for twodifferent values of resistance R1 and R2 (R1 >R2).

Q.9 Answer the following questions(a) Long distance radio broadcasts use short-wave bands. Why?(b) It is necessary to use satellites for long dis-tance TV transmission. Why?

Q.10 In a Young's double-slit experiment, theslits are separated by 0.28 mm and the screenis placed 1.4 m away. The distance between thecentral bright fringe and the fourth brightfringe is measured to be 1.2 cm. Determine thewave length of light used in the experiment.

Q.11 If the output of a 2 input NAND gate is fedas input to a NOT gate, name the new logicgate obtained and write its truth table.

Q.12 A TV transmitting antenna is 81m tall.How much service area can it cover if thereceiving antenna is at the ground level.

SECTION-CQ.13 Consider a uniform electric field E = 3 ×103 îN/C. (a) what is the flux of this field through asquare of 10 cm on a side whose plane is par-allel to the yz plane. (b) what is the flux through the same squareif the normal to its plane makes a 60° anglewith the x-axis?

Q.14 A spherical conducting shell of innerradius r1 and outer radius r2 has a charge Q.(a) A charge q is placed at the centre of theshell. What is the surface charge density onthe inner and outer surfaces of the shell? (b) Is the electric field inside a cavity (with nocharge) zero, even if the shell is not sphericalbut has any irregular shape? Explain.

Q.15 With the help of labelled circuit diagram,explain full wave rectification using junctiondiode. Draw input and output waveforms?

Q.16 (a) A magnetic field that varies in magni-tude from point to point but has a constantdirection (east to west) is set up in a chamber.A charged particle enters the chamber andtravels undeflected along a straight path withconstant speed. What can you say about theinitial velocity of the particle?(b) A charged particle enters an environmentof a strong and non-uniform magnetic fieldvarying from point to point both in magnitudeand direction, and comes out of it following acomplicated trajectory. Would its final speedequal the initial speed if it suffered no colli-sions with environment.(c) An electron travelling west to east enters achamber having a uniform electrostatic fieldin north to south direction. Specify the direc-tion in which a uniform magnetic field shouldbe set up to prevent the electron from deflect-ing from its straight line path.

OR

A charged particle having a charge q is mov-ing with a speed v along the x-axis. It enters aregion of space where an electric field E alongy-axis and a magnetic field B are both present.The particle, on emerging from this region, isobserved to be moving along the x-axis only.Obtain an expression for the magnitude of Bin terms of v and E. Also give the direction ofB

Q.17 An inductor L, a capacitor 20 F, a resist-ance 10ohms are connected in series with anac source of frequency 50 Hz. If the current isin phase with voltage, calculate the induc-tance L.

Q.18 (a) what are eddy currents(b) write applications of eddy currents(c) How they can be minimised

ORIn free oscillations of LC circuit , show thatenergy stored in inductor and capacitor areindependent of time

Q.19 (a) Draw a labeled diagram to show thefinal image formed by compound microscopeat near point.(b) Distinguish reflecting and refracting tele-scopes

OR(a) Define limit of resolution and resolvingpower of microscope(b) Distinguish interfernace and diffraction

Q.20 Figureshows anequiconvex lensof refractiveindex 1.50 in con-tact with a liquidlayer on top of aplane mirror. Asmall needlewith its tip onthe principal axis is moved along the axis untilits inverted image is found at the position ofthe needle. The distance of the needle from thelens is measured to be 45.0 cm. The liquid isremoved and the experiment is repeated. Thenew distance is measured to be 30.0 cm. whatis the refractive index of the liquid?

Q.21 Draw the labeled graphs to show the fol-lowing concerning photo-electric emission(a) Variation of photo current with stoppingpotential(b) Vatiation of stopping potential with fre-quency of incident radiation(c) The work function of material

Q.22 A hydrogen atom initially in the groundlevel absorbs a photon, which excites it to n=4level. Determine the frequency and wave-length of photon.

Q.23 The Q value of a nuclear reaction A + bC + d is defined by

Q = [ mA+ mb mC md]c2 where the massesrefer to the respective nuclei. Determine fromthe given data the Q-value of the followingreactions and state whether the reactions areexothermic or endothermic.

ORDraw a curve between mass number and bind-ing energy per nucleon. write any threesalient features of this curve. Hence define

binding energy.

Q.24 What is amplitude modulation and withlabeled diagram show how an amplitude mod-ulated wave is detected.

SECTION-DQ.25 a) what is cyclotron? Explain its workingprincipleb) A cyclotron's frequency is 10MHZ. Whatshould be the operating magnetic field foraccelerating protons? If the radius of its deesis 20cm. What is the kinetic energy of the pro-ton beam produced by the accelerator.

ORa) Draw a labelled diagram of a moving coilgalvanometer. prove it in a radial magneticfield, the deflection of the coil is directly pro-portional to the current flowing in the coil.b) A galvanometer can be converted into volt-meter to measure upto

1) V volts by connecting a resistance R1 inseries with the coil

2) V/2 volts by connecting a resistance R2

in series with the coil and find R in terms of R1

and R2 required to convert it into voltmeterthat can read upto 2 volts.

Q.26 a) In YDSE, deduce the conditions forobtaining constructive and destructive inter-ference fringes. Hence deduce the expressionfor fringe width.b) Show that the fringe pattern on the screenis actually a superposition of slit diffractionfrom each slit.c) What should be the width of each slit toobtain 10 maxima of double slit pattern within the central maxima of the single pattern forgreen light of wavelength 500nm, if the seper-ation between the slits is 1mm?

ORa) State Brewster's law? Using this prove thatat polarizing angle of incidence, the reflectedand transmitted rays are perpendicular toeach other.b) what are polaroids and write its usesc) What type of waves show the property ofpolarization and name two methods to pro-duce plane polarized light.

Q.27 a) State briefly the processes involved inthhe formation of p-n junction explainingclearly how the depletion region is formed.b) Using the necessary circuit diagrams, showhow V-I characterstics of p-n junction diodeare obtained in 1) forward biasing 2) reversebiasing.c) How these characterstics are made use inrectification

ORa) Why the base junction of transister is light-ly dopedb) Explain the working of p-n-p transistorwhen connected in CE configurationc) Using graphs how amplification factor andresistance gain can be determined.

GENERAL INSTRUCTIONS All questions are compulsory. There are 27questions in all.

There are four sections: A, B, C and D

Section A contains five questions of onemark each, Section B contains seven questionsof two marks each, Section C contains 12 ques-tions of three marks each, and Section D con-tains three questions of five marks each.

There is no overall choice. However, internalchoices have been provided in two questionsof one mark, two questions of two marks, fourquestions of three marks and three questionsof five marks weightage. You have to attemptonly one of the choices in such questions.

You may use the following values of physical constants wherever necessary

These questions and the marks alongside aremeant for practice purpose only. Students areadvised to check format, syllabus and marks

for Board test papers with their teachers.Questions have been given by teachers and

NIE is not responsible for them.

GET CHARGED TO TACKLE PHYSICSThe Physics faculty of Silver Oaks International School, Hyderabad, presents a question paper for you to practice on...

MOCK PAPERPHYSICS PAPERCLASS XII, CBSE

MARKS: 70, TIME: 3Hrs

QDescribe briefly the study planyou followed while preparing

for the Boards?

I practised 10-15 question papersfrom previous years. I wrote mockexams and timed myself. Most im-portantly, I stuck to NCERT. I believeit is sufficient if we do well in theseexercises.

QWhat were the key challengesyou faced and how did you

tackle them?

The challenges I faced included timemanagement mainly because ini-tially, I found it difficult to maintainbrevity in my answers. But after go-ing through the answer keys for theprevious years papers, I think I couldpredict what answers were expected

from students.

QHow did you dealwith pressure to

perform, and keepyourself motivated?

I think peer pressure issomething we all face. Inmy case, it motivated meto study harder. I suggestthat students take peerpressure positively. Myparents and teachers alsoplayed a critical role inencouraging me.

QHow did you bal-ance academics

with other activities?

Music is my passion.

Singing and listening to mu-sic served as stress bustersfor me. It helps to clear my

mind and makes me feelinvigorated.

QWhat tips would you give future

aspirants?

Everybody has their ownways to achieve success.But I think it all boilsdown to hard work andfocus. Staying away

from social media is anadded advantage toavoid any kind of dis-

traction.No matter what, have faith

in yourself and stay hap-py. Eat well, sleep well.

Ananya R Burliof BGS National Public

School, Hulimavu,Bengaluru shares how

she aced her XII CBSE Boards

‘A positive spin on peer pressure helps’

While studyingthere can bevarious dis-

tractions rangingfrom the constantlybuzzing notificationson the mobile phoneto the doorbell ring-ing. On the contrary,

I believe that the eerie silence in theroom is the biggest distraction. Thank-fully, this silence is broken quite a num-ber of times by the whirring of the fanor the sound of the birds. I find that thesilence creates a very unusual feeling, leading to the mind wander-ing. So I tackle this by reading books aloud. This not only helps mefocus on what I am reading but also leads to a better understandingof the concept at hand.

Divij Dodeja, Class X, Nalanda Public School, Mulund (E), Mumbai

BATTLING MIND GAMESMy biggest distraction is my mind.

Of course it's always easier toblame external sources of dis-

turbance like the mobile phonewhich is buzzing with notifi-cations and updates or evenmy iPad as it seems to beinviting me to the landof games. But, I guessthese are mere excus-es my mind seeks. Iam no saint, but I amtrying my own waysof finding solutionsand it has helped. Itell my mind to focus,I try to discipline it. Ifocus on reading what-ever is at hand as ithelps to keep the dis-tractions to the bare min-imum.

Apurva Singh, Class VIII, BombayScottish Powai

Silence is notgolden to me!

Rubai Mustaq, Class 8, Vidya Valley School, Pune

■ Our Class 7 had done aPhysics project onConstellations. We weredivided into groups andeach group chose a differ-ent constellation to workon. We researched thetopic, and made models ofthe various constellationsat school. We then made apresentation on the history,the formation, and thecharacteristics of the constellations we hadworked on.

■ Mine was a group of six,and we chose the constella-tion Cygnus (The Swan). Wehad to give some informa-tion about it in the form ofa chart.

■ To make the model we

used a small portion ofcanvas which we paintedto look like the night sky.

■ To represent the mainstars of the constellationwe used board pins. Wecovered the pins with alu-minium foil and stuckthem firmly on the canvasin the shape of Cygnusand connected all the pinswith a silver thread.

STARRY NIGHTS

MY SCHOOL PROJECT CONSTELLATIONS

THE SWAN

Cygnus is the 16th largestconstellation, occupying

an area of 804 squaredegrees. It is an easilyrecognisable constellation.Its brightest star, Deneb,forms one vertex of theSummer Triangle asterism.Cygnus appears as a ‘T’-shaped grouping of stars,with a fainter star Albireomaking the T into a cross.Hence, it is sometimes knownas theNorthernCross.

■ My team and I had a lot of fun while making this project. We learnta lot about the constellation itself as well as the fascinating historybehind it. All through our work on this project, we learnt so manynew things about every constellation.