45406 + Interview Questions in Physics in Class 12

1.	A particle of mass m is thrown horizontally from point P , as shown in the figure, with speed 5 m//s. It strikes an inclined plane perpendicularly as shown. The inclination of the plane is 30^(@) with the horizontal. Then, the height h shown in the figure is ( Take g = 10 m//s^(2) ) .
Answer» 3.75m 5.0m 4.75m 0.417m Answer :A

Discussion

2.	If L and C denote inductance and capacitance then the quantity L//C has the same dimension as
Answer» TIME `("time")^(-1)` RESISTANCE `xx` time `("resistance")^(2)` ANSWER :A

Discussion

3.	Lactose is disaccharide of
Answer» `ALPHA`-Dglucose-GLUCOSE and `alpha`-D-fructose `BETA`-D--glucose and `beta`-D-galactose `alpha`-Dglucose-glucose and `beta`-D-ribose `beta`-D--glucose and `beta`-D-galactose Solution :LACTOSE is a dissacharide of `alpha`-D-glucose and `beta`-D galactose

Discussion

4.	Two conducting spheres of same radius r are having charges q_1 and q_2 the ratio of their intensities is :
Answer» `E_1/E_2=q_1/q_2` `E_1/E_2=q_1^2/q_2^2` `E_1/E_2` `E_1/E_2=q_1sqrtq_2` ANSWER :A

Discussion

5.	Assertion: Kinetic energy of photoelectrons emitted by a photosensitive surface depends upon the frequency of incident photons, provided that it is greater than the threshold frequency. Reason: Number of photoelectrons depends on the intensity of incident radiation.
Answer» If both assertion and reason are TURE and the reason is the CORRECT explanation of the assertion. If both assertion and reason are true but reason is not the correct explanation of the assertion. If assertion is true but reason is FALSE If the assertion is false but reason is true Answer :B

Discussion

6.	A photocell is illuminated by a small bright source placed 1 m away. When same source of light is placed 1/2 m away, the no. of photoelectrons emitted would :
Answer» DECREASE by a FACTOR of 2 increase by a factor of 2 decrease by a factor of 4 increase by a factor of 4. Solution :`Iprop (1)/(R^(1)), "when" r.=(r)/(2)` `I.=4I`

Discussion

7.	A capacitor is an arrangement for storing large amounts of electriccharge and hence electric energy in a small space. The electrical capacitance of a capacitor is relatedto its abillity to storeelectriccharge. We definecapacity of a conductor as the ratio of charge Q givento the conductorto the rise in its potential,V i.e., C = Q//V. The capacity of an isoltedspherical conductor of radiusr is C = 4pi in_(0) r. In case of a parallel plate capacitor, C = (in_(0)A)/(d) where A is area of insulatedmetal plateand d is distance betweenthe plates. Clearly, capacitydepends on size of capacitor. When different capacitors are connectedin series, capacity, C_(s) = (C_(1) C_(2))/(C_(1) + C_(2)) and when capacitors are connected in parallel, C_(p) = C_(1) + C_(2) Read the above passage and answer the following questions : (i) From C = (Q)/(V), we find that C can beincreased Q or decresingV. Do youagree ? (ii) Capacity of a capacitor is fixeddependingon its geometry and the medium used. Is it true ? (iii) Calculatethe capacity of a condenser which when connected in series with a conductor of 12 muF gives us a capacitance of 3 muF. (iv) What values of lifedo yo+-earn from this study ?
Answer» Solution :No, we do AGREE. This is becausecapacitanceC is fixed, dependingon geometry fo condeaser. If we increaseQ , Vincreases but C remainsconstant and vice-versa. (ii) yes, the statement is true. (iii) Here, `C_(1) = ? C_(2) = 12 MUF, C_(s) = 3 muF` From `C_(s) = (C_(1) C_(2))/(C_(1) + C_(2))` `3 = (C_(1) xx 12)/(C_(1) + 12) or 12C_(1) = 3C_(1) + 36 C_(1) = 4muF` (iv) Just as capacity fo a condenser is fixeddependingon its geometry, similarly capacity of a person to execuitesome workis fixeddependingon his buit up. Capacity increases by connectingthe CAPACITORS in parallel. exactly in the same way capacity of a group of persons can be increased wheneach ONEOF themis connectedto the same sources , e.g., guideor instractor. This is the implication of this concept in day to day life.

Discussion

8.	The image formed by a convex mirror of a real object is larger than the object ( u = object distance, f = focal length )
Answer» a when `u LT 2f` b when `u GT 2f` c for all VALUES of u d for no value of u SOLUTION :For all POSITION of object the image formed by a convex lens is smaller than the size of the object.

Discussion

9.	The position vector of a particle is vecr=(acosomegat)hati+(asinomegat)hatj. the velocity of the particle is
Answer» DIRECTED TOWARDS the origin directedaway from the origin parallel to the POSITION vector perpendicular to the position vector. Answer :D

Discussion

10.	A rectangular coil is made of 100 turns and has dimension of 50 cm xx 20 cm, carrying a current of 10A It is placed inside a magnetic field of 5 T making an angle of 30^(@)with the field. What is the torque acting on the coil?
Answer» Solution :Given, current through the coil , `I = 10 A` Area of coil , `A = 50 xx 20 = 1,000cm^(2) = 0.1 m^(2)` Angle between NORMAL to the coil and magnetic field, ` theta = 90^(@) - 30^(@) = 60^(@)` Number of turns, ` N = 100` Torque EXPERIENCED by the coil will be: ` tau = NIAB sin theta` ` = 100 xx 10 xx 0.1 xx 5 sin 60^(@)` ` = 500 xx sqrt3/2 = 433` Nm

Discussion

11.	A man weighs 50 kg at earth'ssurface. At what height above the earth's surface his weight becomes half (Radius of earth = 6400 km) :
Answer» 2526 km 6400 km 2650 km 3200 km. Solution :`(mg.)/(mg)=(1)/(2) rArr (g.)/(g)=(1)/(2)` or `(R^(2))/((R+H)^(2))=(1)/(2) rArr (R )/(R+h)=(1)/(sqrt(2))` `therefore sqrt(2)R=R+h` `h=(sqrt(2)-1)R=0.414xx6400=2650` km. Thus CORRECT CHOICE is (c ).

Discussion

12.	The meaning of 'mortal....
Answer» That which can die That which cannot LIVE forever That which has LIMITED time All of the above Answer :D

Discussion

13.	In Young's double slit experiment if the distance between two slits is equal to the wavelength of used light. Then the maximum number of bright fringes obtained on the screen will be ......
Answer» 2 5 7 infinite Solution :Condition for bright fringe (maxima) `d SIN theta= n lambda` `:. Lambda sin theta= n lambda "" [ :. d= lambda]` `:. Sin theta=n` but `sin theta le1` here `n le 1` `:.` POSSIBLE VALUE ofn is -1,0,1 `:.` TOTAL three maxima will be obtained.

Discussion

14.	The binding energy per nucleon is maximum at A=56 and its value is around_____ Mev/ Nucleon
Answer» 8.4 8.7 9 7.8 Answer :B

Discussion

15.	A motor cycle starts from rest and accelerates along a straight path at 2 m/s^(2). At the starting point of the motoer cycle there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at 94% of its value when the motor cycle was at rest ? (speed of sound = 330ms^(-1) )
Answer» 146 m 196 m 49 m 98 m Solution :For observer moving AWAY from source ` V. = ((V- v)/(V)) ` y ` (94)/(100) V = (V - v)/(V) ` V `rArr "" 94 V =100 V - 100 v` `rArr "" 100v = 6 `v 100v= 6V `v = (6 xx 330)/(100) = 19.8` m/s Now `v^(2) - u^(2) = ` 2AS `rArr (19.8)^(2) - 0 = 2 xx 2s` S= 96 m `rArr ` CHOICE (d).

Discussion

16.	The ration of coulomb force and nuclear force between two protons inside a nucleus is
Answer» `1:100` `1:10^(4)` `1:10^(7)` `1:10^(36)` ANSWER :a

Discussion

17.	In a stationary waves are variation in pressure at nodes is :
Answer» TWICE that DUE to ONE WAVE THRICE that due to one wave zero maximum. Answer :D

Discussion

18.	Five bulbs B_(1), B_(2), B_(3) and B_(4) each of rating 60W//200V and B_(5) of rating 120W//400V are connected as shown in circuit. Total consumption by all the bulbs is :
Answer» `240 W` `270 W` `90 W` `180 W` SOLUTION :`P_(B_(1)+B_(2))=30W` `P_(B_(3))=60W,P_(B_(4))=60W` `P_(B_(5))=((200)^(2))/((400)^(2)/(120))=(120)/(4)=30W` `P_(TOTAL)=180W`

Discussion

19.	A star is moving towards the earth with a speed of 4.5 xx 10^(6) m/s.If the true wavelength of a certain line in the spectrum received from the star is 5890 Å, its apparent wavelength will be about [ c = 3 xx 10^(5) m/s].
Answer» `5890 Å` `5978 Å` `5802 Å` `5896 Å` Solution :`lambda. = lambda(1 -(V)/(c)) = 5890 (1 - (4.5 xx 10^(6)))/(3 xx 10^(8)) approx 5802 Å`

Discussion

20.	The ration of contributions made by the electric field and magnetic field components to the intensity of an EM wave is
Answer» `C:1` `C^(2):1` `1:1` `SQRT(c:1)` ANSWER :C

Discussion

21.	The rate of disappearence of SO_(2) in the reaction 2SO_(2)+O_(2)to2SO_(3) is 1.28xx10^(-3) g litre^(-1) sec^(-1) Then the rate of formation of SO_(3) in g litre^(-1) sec^(-1) is
Answer» `0.64xx10^(3)` `0.80xx10^(3)` `1.28xx10^(-1)` `1.60xx10^(-3)` SOLUTION :`=-(d[SO_(2)])/(DT)=1.28xx10^(-3)GL^(-1)s^(-1)` `=(1.28xx10^(-3))/64Ms^(-1)` `-(d[SO_(2)])/(dt)=(d[SO_(3)])/(dt)` `(1.28xx10^(-3))/64ML^(-1)s^(-1)` `(1.28xx10^(-3))/64xx80gL^(-1)s^(-1)` `=1.6xx10^(-3)gL^(-1)s^(-1)`

Discussion

22.	A magnet of magnetic moment 0.1 Am^(2) is placed in a uniform magnetic field 0.36 xx 10^(-4) T. The force acting on its each pole is 1.44 xx 10^(-4) N. The distance between two poles would be ...... cm.
Answer» `1.25` `2.5` `5.0` `1.8` SOLUTION :`F= PB` `therefore p =(F)/( B) = (1.44 xx 10^(-4))/( 0.36 xx 10^(-4) ) ""…(1)` `therefore p = 4 Am` Now `m= 2pl` `therefore 2L = (m)/( p) ""…(2)` `= (0.1)/(4)` `=0.025` m `=2.5 cm`

Discussion

23.	What is the meaning of 'dawn'?
Answer» LIGHT Darkness First light of the day Last light of the day Answer :C

Discussion

24.	A barmagnet is placed north southwith its nort poledue norththe pointsof zero magnetic field will be in whichdirection fromcentre of magnet
Answer» north and SOUTH EAST and west north east and south west north east and south east ANSWER :B

Discussion

25.	The viscosity of liquids is due to
Answer» ADHESIVE force Cohesive force Gravitational force Diffusion Answer :B

Discussion

26.	A rectangular coil of 500 turn 10^(-2)m^(2) area carrying 1 A is in a magnetic field of 1 T at 60° to its plane. The net rotating effect it could experience in (Nm) is
Answer» 250 25 2.5 0.25 Answer :C

Discussion

27.	The dimensional formula of1/(mu_circ^(c^2)) (dϕ_E)/dtis same as that of[where Φe is same as that of [where ϕ_E is electric flux and c is speed od light,t is time and μ_0 is permeability of free space)
Answer» CURRENT ELECTRIC potential capacitance charge Answer :D

Discussion

28.	A p-n diode can be used as
Answer» CONDENSER REGULATOR AMPLIFIER RECTIFIER ANSWER :d

Discussion

29.	A plano covex lens fits exactly in to a plano concave lens. Their plane surface are parallel to each other. If the lenses are made of different materials of refractive indices mu_(1) and mu_(2) and R is the radius of curvatureof the curved surfaces of the lenses then the focal length of the combination is
Answer» `R/(mu_(1)-mu_(2))` `(2R)/(mu_(1)-mu_(2))` `R/(2(mu_(1)-mu_(2)))` `R/(mu_(1)+mu_(2))` ANSWER :A

Discussion

30.	Permanent magnets are madeof steel because steel has
Answer» lowretentivity and lowcoercive field highretentivity and high coercive field low RETENTIVE and high coercive field high RETENTIVITY and lowcoercive field Answer :B

Discussion

31.	Energy stored in electromagnetic waves in the form of
Answer» ELECTRICAL energy MAGNETIC energy both electrical and magnetic energy neither electrical nor magnetic energy. Solution :Electromagnetic WAVES POSSESS both electrical energy and magnetic energy and magnetic energy.

Discussion

32.	Thebob of a simple pendulum is a spherical hollow ball filled with water. A plugged hole near the bottom of the oscillatingbob getssuddenlyunplugged. During observation,till water is coming out, the time period of oscillation would :
Answer» first increase and then decrease to the original value first decrease and then increase to the original value remain unchanged increase towards a SATURATION value Solution :Time period `T=2pi sqrt((L)/(G))` EFFECTIVE length of the pendulum first increases and then DECREASES to the original value due to shifting of centre of gravity. So time period, first increases and then decreases. So correct choice is a.

Discussion

33.	A proton and an alpha-particle are accelerated through the same potential difference. The ratio of de-Broglie wavelength of proton to the de-Broglie wavelength of alpha particle will be
Answer» <P>`1 : 2` `2 sqrt(2) : 1` `2 : 1` `1 : 1` Solution :`lambda = (h)/(sqrt(2mqV))` `(lambda_(p))/(lambda_(alpha)) = sqrt((2m_(alpha) q_(alpha) V)/(2m_(p)q_(p)V)) = sqrt((2 xx 4m_(p) xx 2E xx V)/(2m_(p) xx e xx V)) = 2 sqrt(2) : 1`

Discussion

34.	What does X stand for in the given reaction ? ""_(20)Ca^(41) rarr ""_(20)Ca^(40)+X.
Answer» Proton Electron Neutron `ALPHA`-particle. Answer :C

Discussion

35.	Ionized hydrogen atoms and alpha-particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r_(H):r_(alpha) will be :
Answer» `1:4` `2:1` `1:2` `4:1` Solution :Here `q_(H)=eandq_(alpha)=2e` For CIRCULAR motion, `(mv^(2))/R=Bqv` `thereforer=(mv)/(BQ)" "(because"m,V,B are constant")` `thereforerprop1/q` `thereforer_(H)/r_(alpha)=q_(alpha)/q_(H)=(2e)/e=2/1`

Discussion

36.	A point source of light is placed 4m below the surface of a transparent liquid of refractive index (5)/(3). The minimum diameter of a disc which should be placed over the source on the surface of liquid to cut off all light coming out of liquid is :
Answer» 1 m 3 m 4 m NONE of these. ANSWER :D

Discussion

37.	When a current flow through a metallic conductor of non-uniform area of crossection,the quantity that remains constant along the condutor is
Answer» current current density electric field drift velocity Answer :A

Discussion

38.	A: The value of potentialenergydepends on thereference takenfor zeropotential energy. R : The valueof changein potentialenergyisindependentfromreferencelevel .
Answer» If both ASSERTION & Reasonare true . Andthe REASONIS the CORRECT explanationof theassertion , then mark (1) If both Assertion & Reason are truebut thereasonis NOTTHE correct explanation of the assertion , then mark(2) If Assertionis truestatementbut Reason is false ,then mark (3) It will movethe samespeed , tangentiallyto the spacecraft Answer :B

Discussion

39.	Energy in the ground state of hydrogen atom is -13.6 eV. What is the energy in the first excited state ?
Answer» SOLUTION :Energy of hydrogen ATOM in NTH orbit is `E=-(13.6)/(n^(2))eV` For Ist excited STATE, `n=2` `E=-(13.6)/(4)=-3.4 eV`

Discussion

40.	An object is x times, the focal length ofa concave mirror away from the principal focus. Show that the image will be (1)/(nx) times the focal lehght of mirror away from principal focus, where n is :
Answer» `(1)/(2)` `(1)/(3)` 1 1.5 Solution :(c ) Let focal length of mirror = - F `therefore U = - f - fx = - (X + 1) f` `(1)/(f) = (1)/(u) + (1)/(v)` `therefore (1)/(v) = (1)/(f) - (1)/(u) = (1)/(-f) + (1)/((x+1)f)` `=(-x-1+1)/((x+1)f)=-(x)/((x+1)f)` `v=-((x+1)f)/(x)=-(1+(1)/(x))f=-(1+(1)/(x))f.` Distance of image from Principa focus is `= (1)/(x) xx f = (1)/(x)` times the focal lenght `therefore n = 1`

Discussion

41.	A parallel beam of light is incident on a rectangle transparent plate of thickness 8 cm. The angle of incidence and refraction of the beam is 60^@and 30^@ respectively. Find the lateral shift.
Answer» SOLUTION :`(8)/( SQRT(3)) CM`

Discussion

42.	The length of the astronomical telescope is 40cm and has magnifying power7. Find the focal length of the lenses.
Answer» SOLUTION :`f_0+f_0` = 40, `f_0/f_e` = 7 or `f_0` = `7f_e` `7f_e` = `f_e` = 40, `f_e` = 40/8 = 5CM `f_0` = `7xx5` = 5cm

Discussion

43.	A 1.9 H inductor, a 100 mu F capacitor and 25 Omega resistor are connected in series to an a.c. source whose e.m.f. (in volt) varies with time t (in seconds) according to the expression E = 282 sin 100t. Determine (i) the reactance, (ii) th the impedance (iii) the r.m.s. value of the current and (iv) the rate of dissipation of heat
Answer» ANSWER :(i) `90 Omega` ; (II) `93.4 Omega` ; (iii) 2.135 A and (IV) 113.95 W

Discussion

44.	The velocity of a moving galaxy is 300 kms^(-1) and the apparent change in wavelength of a spectral line emitted from the galaxy is observed as 0.5 nm. Then the actual wavelength of the spectral line is
Answer» 3000 Å 5000 Å 6000 Å 5500 Å Answer :B

Discussion

45.	Long range radio transmission is possible when the radiowaves are reflected from the ionosphere For this to happen the frequency of the radio waves must be in the range :
Answer» 1-3 MHz 150-500 kHz 8-25 MHz 80-150 MHz Answer :C

Discussion

46.	A point object is moving uniformly towards the pole of a concave mirror of focal length 25 cm along its axis as shown below. The speed of the object is 1 m s^(-1). At t = 0, the distance of the object from the mirror is 50 cm. The average velocity of the image formed by the mirror between time t = 0 and t = 0.25 s is
Answer» Zero 40 cm `s^(-1)` INFINITY 20 cm `s^(-1)` SOLUTION :(c): At t = 0, u = 50 cm (PLACED at 2f), v = 50 cm After 25 s, u = 50 – 25 = 25 cm (object is at f), v=infinity So, velocity of IMAGE = `("infinity" -50)/(25)` = infinity

Discussion

47.	According to Bohr's theory of the hydrogen atom, the speed v_(n) of the electron in a stationary orbit is related to the principal quantum number n as(c is a constant)
Answer» `v_(n) = C/(n^(2))` `v_(n) = c/n` `v_(n) = c xx n` `v_(n) = c xx n^(2)` SOLUTION :SPEED of ELECTRON in `n^(th)` orbit, `upsilon _(n) = c/n`

Discussion

48.	Answer the following questions: Light of wavelength 5000 A propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected ?
Answer» SOLUTION :A photodiode (for special purpose) is fabricated with a transparent window to allow light to fall on the junction of the diode. When the junction of photodiode is reverse bias it is ILLUMINATED with light of energy `hv gt E_(g)` of the semiconductor, the ELECTRON-hole pairs are generated due to absorption of photon. Due to electric field of the function, electron are collected in n side and holes are collected on p-side and PRODUCES an emf. When an external load is connected, an electric current flows in the external circuit. The magnitude of the electric current depends on the intensity of incident light. Reason of Reverse Biasing : If there is no illumination, majority electrons are more than minority holes in n region of the diode. On illumination the junction, some electrons-hole pairs are generated. Let the excess electrons and holes generated are DN and Dp respectively So. at a particular illumination, `n'=n+Delta n` and`p'=p+Delta p` Since, `Delta n = Delta p` and `n gt p` Hence, `= (Delta n)/(n) lt lt (Delta P)/(P)` It means the minority carriers dominated reverse bias current is more easily measurable, than change in the forward bias current. Hence, photodiodes are preferably used in the reverse bias light intensity.

Discussion

49.	Find the total flux due to charge q associated with the given hemispherical surface
Answer» (a) `(Q)/(2 in_(0))`, (b) 0, (C ) `(q)/(in_(0))`, (d) 0 (e )0 (a) 0, (b) `(q)/(2 in_(0))`, (c ) 0, (d) `(q)/(in_(0))`, (e )0 (a) `(q)/(2in_(0))`, (b) `(q)/(in_(0))`, (c ) 0, (d) `(q)/(in_(0))` , (e ) 0 (a) 0, (b) `(q)/(2 in_(0))`, (c ) 0, (d) `(q)/(in_(0))`, (e ) `(q)/(in_(0))` ANSWER :A

Discussion

50.	The rms value of voltage of an alternator is 200 V and the rms current delivered by it to a load is 3A. If the phase angle between the current and voltage is pi//6, find the power.
Answer» Solution :The power in ac circuits is given by `P=E_("RMS")I_("rms") COS phi`. Here `E_("rms")=200V`, `I_("rms")=3Aand phi=pi//6=30^(@)` `therefore P=200xx3xx(SQRT3)/(2)=300sqrt3=519.6W`

Discussion

Explore topic-wise InterviewSolutions in Current Affairs.

A particle of mass m is thrown horizontally from point P , as shown in the figure, with speed 5 m//s. It strikes an inclined plane perpendicularly as shown. The inclination of the plane is 30^(@) with the horizontal. Then, the height h shown in the figure is ( Take g = 10 m//s^(2) ) .

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A magnet of magnetic moment 0.1 Am^(2) is placed in a uniform magnetic field 0.36 xx 10^(-4) T. The force acting on its each pole is 1.44 xx 10^(-4) N. The distance between two poles would be ...... cm.

What is the meaning of 'dawn'?

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Ionized hydrogen atoms and alpha-particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r_(H):r_(alpha) will be :

A point source of light is placed 4m below the surface of a transparent liquid of refractive index (5)/(3). The minimum diameter of a disc which should be placed over the source on the surface of liquid to cut off all light coming out of liquid is :

When a current flow through a metallic conductor of non-uniform area of crossection,the quantity that remains constant along the condutor is

A: The value of potentialenergydepends on thereference takenfor zeropotential energy. R : The valueof changein potentialenergyisindependentfromreferencelevel .

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An object is x times, the focal length ofa concave mirror away from the principal focus. Show that the image will be (1)/(nx) times the focal lehght of mirror away from principal focus, where n is :

A parallel beam of light is incident on a rectangle transparent plate of thickness 8 cm. The angle of incidence and refraction of the beam is 60^@and 30^@ respectively. Find the lateral shift.

The length of the astronomical telescope is 40cm and has magnifying power7. Find the focal length of the lenses.

The velocity of a moving galaxy is 300 kms^(-1) and the apparent change in wavelength of a spectral line emitted from the galaxy is observed as 0.5 nm. Then the actual wavelength of the spectral line is

Long range radio transmission is possible when the radiowaves are reflected from the ionosphere For this to happen the frequency of the radio waves must be in the range :

According to Bohr's theory of the hydrogen atom, the speed v_(n) of the electron in a stationary orbit is related to the principal quantum number n as(c is a constant)

Answer the following questions: Light of wavelength 5000 A propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected ?

Find the total flux due to charge q associated with the given hemispherical surface

The rms value of voltage of an alternator is 200 V and the rms current delivered by it to a load is 3A. If the phase angle between the current and voltage is pi//6, find the power.