cbse class 12 outside physics 2005

8/11/2019 CBSE Class 12 Outside Physics 2005

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PHYSICS 2005

Q. 1.An electric dipole of dipole moment 20, X 10-6C.m is enclosed by a closed surface. What is

the net flux comin out of the surface! 1

Q. 2. An electron beam pro"ected alon #X-axis, experiences a force due to a manetic field alon

the #$-axis. What is the direction of the manetic field! 1

Q. 3. %he po&er factor of an a.c. circuit is 0.'. What &ill be the phase difference bet&een (oltaeand current in this circuit! 1

Q. 4.)lectrons are emitted from a photosensiti(e surface &hen it is illuminated by reen liht but

electron emission does not ta*e place by yello& liht. Will the electrons be emitted &hen the

surface is illuminated by +i red liht, and +ii blue liht. 1

Q. 5. What should be the lenth of the dipole antenna for a carrier &a(e of reu- ency / X 1

3! 1

Q. 6. 4efine 5electric line of force5 and i(e its t&o important properties. 2

Q. 7. +a Why does the electric field inside a dielectric decrease &hen it is placed in an external

electric field!

+b A parallel plate capacitor &ith air bet&een the plates has a capacitance of p. What &ill be the

capacitance if the distance bet&een the plates he reduced by half and the space bet&een them is

filled &ith a substance of dielectric constant 76! 2

Or

are *ept at the (ertices, A, 8 and C respecti(ely of

an euilateral trianle of side 20 cm as sho&n in the fiure. What should be the sin and manitude

of the chare to be placed at the mid-point +9 of side 8C so that the chare at A remains in

euilibrium! 2

Q. 8. 4ra& : - ; raph for ohmic and non-ohmic materials. circuit be reater than

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the applied (oltae of the a.c. source! ?ustify yourans&er. 2

Q. 12. %he imae of a candle is formed by a con(ex lens on a screen. %he lo&er half of the lens is

painted blac* to ma*e it completely opaue. 4ra& the ray diaram to sho& the imae formation.

o& &ill this imae be different from the one obtained &hen the lens is not painted blac*! 2

Q. 13. An electric dipole is held in a uniform electric field. +1 @sin suitable diaram, sho& that it

does not undero any translatory motion, and +ii deri(e an expression for the torue actin on itand specify its direction. 3

Q. 14. A al(anometer &ith a coil of resistance 120 ohm sho&s full scale deflection for a current of

2.' mA. o& &ill you con(ert the al(anometer into an ammeter of rane 0 to .' A! 4etermine

the net resistance of the ammeter. When an ammeter is put in a circuit, does it read slihtly less or

more than the actual current in the oriinal circuit! ?ustify your ans&er. 3

Q. 15. 4efine the term 5resisti(ity5 and &rite its B. ; . unit. 4eri(e the expression for the resisti(ity of

a conductor in terms of number density of free electrons and relaxation time. 3

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Btate the principle of potentiometer. 4ra& a circuit diaram used to compare the e.m.f. of t&oprimary cells. Write the formula used. o& can the sensiti(ity of a potentiometer be increased!

Q. 16. )xplain, &ith the help of diaram, the principle and &or*in of an a.c.


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Q. 23. 4istinuish bet&een, analo and diital communication. Write any t&o modulation

techniues employed for the diital data. 4escribe briefly one of the techniues used. 3

Q. 24. 4ra& a schematic diaram of a sinle optical fibre structure. )xplain briefly ho& an optical

fibre is fabricated. 4escribe in brief, the mechanism of propa- ation of liht sinal throuh an

optical fibre.3

Q. 25. (a) With the help of a labelled diaram, explain the principle and &or*in of a mo(in coil

al(anometer.

(b) %&o parallel coaxial circular coils of eual radius 5>5 and eual number of turns 5E5, carry eual

currents 5;5 in the same direction and are separated by a distance 52>5. ind the manitude and

direction of the net manetic field produced at the mid-point of the line "oinin their centres. 5

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(a) Btate 8iot-Ba(art5s la&. @sin this la&, deri(e the expression for the manetic field due to a

current carryin circular loop of radius 5>5, at a point &hich is at a distance 5x5 from its centre alon

the axis of the loop.

(b) %&o small identical circular loops, mar*ed +1 and +2, carryin eual currents, are placed &ith

the eometrical axes perpendicular of each other as sho&n in the fiure. ind the manitude anddirection of the net manetic field produced at the point .

Q. 26. (a) o& is a &a(efront different from a ray! 4ra& the eometrical, shape of the &a(efronts

&hen +i liht di(eres from a point source, and +ii liht emeres out of a con(ex lens &hen a point

source is placed as its focus.

(b) Btate uyens5 Frinciple. With the help of a suitable diaram, pro(e Bnell5s la& of refraction

usin uyens5 Frinciple. 5

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(a) ;n $oun5s double slit experiment, deduce the conditions for +i comstru- cti(e, and +ii

destructi(e interference at a point on the screen. 4ra& a raph sho&in (ariation of the resultant

intensity in the interference pattern aainst position 5x5 on the screen.

+b Compare and contrast the pattern &hich is seen &ith t&o coherently illuminated narro& slits in

$oun5s experiment &ith that seen for a coherently illuminated sinle slit producin diffraction.

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Q. 27. (a) 4istinuish bet&een metals, insulators and semiconductors on the basis of their enery

bands.

(b) Why are photodiodes used preferably in re(erse bias condition! A photodiode is fabricated from

a semiconductor &ith band ap of 2. e:. Can it detect a &a(elenth of 6000 nm! ?ustify. 5

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(a) )xplain briefly, &ith the help of circuit diaram, ho& : - ; characteristics of a p-n "unctiondiode are obtained ii +i for&ard bias, and +ii re(erse bias. 4ra& the shape of the cur(es obtained.

(b) A semiconductor has eual electron and hole concentration of 6 x 10Gm/. n dopin &ith

certain impurity, electron concentration increases to D X1012Gm/.

+i ;dentify the ne& semiconductor obtained after dopin.

+ii Calculate the ne& hole concentration.

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cbse class 12 outside physics 2005

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