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2701.

A classical atom based on ......... is doomed to collapse. (Thomson's model/ Rutherford's model.)

Answer»

SOLUTION :Rutherford.s MODEL
Discussion
2702.

Show that the magnetic field B at a point in between the plates of a parallel-plate capacitor charging is (in_0mu_0r)/2 (dE)/(dt) (symbols having usual meanings).

Answer»

Solution :Let `I_D` be the displacement current in the region between TWO plates
of PARALLEL plate CAPACITOR, Fig. The magnetic field
induction at a point in a region between two plates of capacitor at
`abotr` distance r fromthe axis of plate is
`B=(mu_0)/(4PI) (2I_D)/r=(mu_0)/(2pir) I_D=(mu_0)/(2pir)xxin_0 (d phi_E)/(dt)[ :' I_D=in_0 (dphi_E)/(dt)]`
`=(mu_0in_0)/(2pir) d/(dt) (Epir^2)=(mu_0in_0)/(2pir) pir^2 (dE)/(dt) =(mu_0in_0 r)/2 (dE)/(dt)( :' phi_E=Epir^2)`
Discussion
2703.

How is the working of a telescope different from that of a microscope ? The focal lengths of the objective and eyepiece of a microscope are 1.25cm and 5 cm respectively. Find the position of the object relative to the objective in order to obtain anangular magnificatio of 30 in normal adjustment.

Answer»

Solution :Working differences `:`
1. OBJECTIVE of a telescope forms the image of a vey far off object at, or within, the FOCUS of its eyepiece. The microscope does the same for a small object kept just beyond the focus of its objective.
2. The final image formed by a telescope is magnified relative to its size as SEEN by the unaided eye while the final image formed by a microscope is magnified relative to its ABSOLUTE size.
3. The objective of a telescope has large focal length & large aperture while the corresponding for a microscope have very small values.
Given `:``f_(0) = 1.25cm`
`f_(e ) = 5 cm`
Angular magnification m = 30
Now, `m = m_(e )xx m_(0)`
In normal adjustment , angular magnifucation of eyepiece
`m_(e ) = ( d // f_(e )) = ( 25)/( 5) = 5 `
Hence,`m_(0) = 6`
But `m_(0) = ( v_(0))/( u_(0))rArr =-6 = ( v_(0))/( u_(0))`
`v_(0) = - 6 u_(0)`
Applying lens equation to the objective lens `:`
`(1)/( f_(0)) = ( 1)/( v_(0)) - ( 1)/( u_(0))`
`(1)/( 1.25) = ( 1)/( - 6u_(0)) - ( 1)/( u_(0))`
`(1)/( 1.25) = ( - 1- 6)/( 6u_(0))`
`6 u_(0) = 1.25 xx ( - 7)`
`u_(0) = ( - 12.5 xx 7 )/( 6) cm`
`= 1.46 cm`
Discussion
2704.

Which of the following components of a LCR circuit, with a.c. supply, dissipates energy?

Answer»

L
current is AHEAD of VOLTAGE by `pi/2`
R
all of these

ANSWER :C
Discussion
2705.

An equilateral prism is made of glass whose refractive index for red and violet light is 1.510 and 1.550 respectively. White light is incident at an angle of incidence i and the prism is set to give minimum deviation for red light. Find (a) angle of incidence (b) angular dispersion (i.e., angular width of the spectrum). Given {:(theta=,28^(@),32^(@),50^(@),55^(@)),(sin theta=,0.487,0.529,0.755,0.819):}

Answer»


ANSWER :`5^(@)`
Discussion
2706.

Obtain the resonant frequency and Q - factor of a series LCR circuit with L = 3 H, C=27muF, R=7.4 Omega. It is desired to improve the sharpness of resonance of circuit by reducing its full width at half maximum by a factor of 2. Suggest a suitable way.

Answer»

Solution :Here `L=3H, C=27muF=27xx10^(-6)F and R=7.4Omega`
`therefore"Resonant frequency v, "=(1)/(2pisqrt(LC))=(1)/(2xx3.14sqrt(3xx27xx10^(-6)))=17.7Hz`
`"andQ - factor "=(X_(L))/(R )=(L omega)/(R )=(Lxx2piv)/(R )=(3xx2xx3.14xx17.7)/(7.4)=45`
IMPROVING the resonance of the circuit by reducing its full width at half of maximum power by a factor of 2 means that Q - factor is doubled. The simplest method for this is to reduce the value of resistance R so that
`Q.=2Q rArr (X_(L))/(R.)=2(X_(L))/(R) rArr R.=(R )/(2)=(7.4)/(2)=3.7Omega`
Discussion
2707.

From the information of energy band gaps of diodes, how do you decide which can be light emitting diodes?

Answer»

SOLUTION :For a LIGHT emitting diode the energy band GAP should LIE in visible light range (or `1.8eV le E_(g) le 3.1eV`) .
Discussion
2708.

Obtain Coulomb's law from Gauss's law.

Answer»

Solution :As SHOWN in figure, consider a POINT charge +q kept at O.
A Gaussian surface .S. is shown in figure includes charge q.
Consider surface area`vecds` at point E Here, `vecE || vecds` ds and so that `theta =0^(@)` .
According to Gauss.s law,
`phi =q/epsilon_(0)`
`therefore int vecE.vec(ds) = q/epsilon_(0)`
`therefore intE.ds COS0^(@) =q/epsilon_(0)[therefore vecE || vecds]`
`therefore E=q/(4piepsilon_(0)r^(2))`
`therefore F/q =q/(4piepsilon_(0)r^(2))`
`therefore F = (Kq.q_(0))/r^(2)`
This is Coulomb.s law.
Discussion
2709.

A body of mass 1 kg strikes elastically with another body at rest and continues to move in the same direction with one fourth of its initial velocity. The mass of other body is :

Answer»

3 kg
0.6 kg
2.4 kg
4 kg

Solution :`v_(1)=((m_(1)-m_(2))v_(1)+2m_(2)v_(2))/(m_(1)+m_(2))`
`V/4=((1-m_(2))u+0)/(1+m_(2))`
`implies1+m_(2)=4-4m_(2)implies5m_(2)=3`
`impliesm_(2)=3/5=0.6 kg`
Discussion
2710.

The binding energy of a satellite of mass 1000 kg revolving in circular orbit around the earth when it is at a height 500 km above the surface of the earth is

Answer»

`14.3xx10^9J`
`14.3xx10^9erg`
`1.43xx10^9J`
`1.43xx10^9erg`

ANSWER :C
Discussion
2711.

When a broad cast AM transmitter is 50 percent modulated, its antenna current is 12 A. When the modulation depth is increased to 0.9 the current would be in amperes

Answer»

`4sqrt(11.24)`
`4sqrt(8.24)`
`2sqrt(11.24)`
`6sqrt(8.24)`

ANSWER :A
Discussion
2712.

Which phenomenon concludes that light wave is transverse in nature ?

Answer»

SOLUTION :Polarisation.
Discussion
2713.

Assertion interference shows wave nature of light Reason Photoelectric effect proves particle nature of light.

Answer»


ANSWER :B
Discussion
2714.

What the electric and magnetic fields in electromagnetic waves maintain ?

Answer»

SOLUTION :same PHASE
Discussion
2715.

It is desired to measure the magnitude of field between the poles of field between the poles of a powerful loud speaker magnet. A small flat search coil of area 2cm^(2) with 25 closely wound turns, is positioned normal to the field direction and then quickly snatched out of the field region. Equivalently, one can give it a quick 90^(@) turns to bring its plane parallel to the field direction. The total charge flown in the coil (measured by a ballistic galvanometer connected to the coil) is 7.5mC. The combined resistance of the coil and the galvanometer is 0.50Omega. Estimate the field strength of magnet.

Answer»

Solution :Charge `Q=(N)/(R)(phi_(i)-phi_(F))`
`B=(phi_(i))/(A),phi_(i)=BA`
`phi_(i)=1.5xx10^(-4),phi_(f)=0,N=25,R=0.5`
`Q=7.5xx10^(-3)C,A=2xx10^(-4)m^(2)`
`therefore B=(RQ)/(NA)=(0.5xx7.5xx10^(-3))/(25xx2xx10^(-4))=(5xx7.5)/(50)`
i.e., `B=0.75T`
Discussion
2716.

The number of waves contained in a unit length of the medium is called .....

Answer»

elastic WAVE
wave NUMBER
wave pulse
electromagnetic wave

Solution :The number of waves CONTAINED in a unit LENGTH of the medium is called a wave number
Discussion
2717.

A short linear object of length l lies on the axis of a spherical mirror of focal length f, at a distance x from the mirror. Then, the length of the image (P) so obtained will be

Answer»

`(If)/((X-f))`
`(If^(2))/((x-f)^(2))`
`(If)/x`
`(I(x-f))/x`

Solution :(b) Here `u=-x,F=-f`
`:' 1/V+1/u=1/F`
or `1/v-1/x=-1/f` or `1/v=1/x-1/f=(f-x)/(XF)`
`:.v=(xf)/(f-x)`
`:. (Deltav)/(DELTAU)=(v^(2))/(u^(2))=((xf)/(f-x))^(2)xx1/(x^(2))=(f^(2))/((f-x)^(2))`
`:. Deltav=(f^(2)l)/((x-f)^(2))` [ `:' Deltau=l`]
Discussion
2718.

A prism made of refractive index x has prism angle of 50^(@). A light ray incident at an angle of 45^(@) refracts through the prism and undergoes minimum deviation. Calculate the value of x and angle of minimum deviation.

Answer»

SOLUTION :`40^(@), 1.67`
Discussion
2719.

A particles of rest mass m_0 with kinetic energy T strikes a stationary particle of the same rest mass. Find the rest mass and the velocity of the compound particle formed as a result of the collision.

Answer»

SOLUTION :`M_0c^2=SQRT(E^2-c^2p^2)`
`sqrt((2m_0^2+T)^2-T(2m_0c^2+T))=sqrt(2m_0c^2(2m_0c^2+T))=csqrt(2m_0(2m_0c^2+T))`
ALSO `cp=sqrt(T(T+2m_0c^2)), V=(c^2p)/(E)=csqrt((T)/(sqrt(T+2m_0c^2))`
Discussion
2720.

A diatomic molecules is made of two masses m_(2) and m_(2) which are separated by a distance r. We calculate its rotational energy by applying Bohr's rule of angular momentum quantization, its energy will be given by (n is an integer)

Answer»

`((m_(1)+m_(2))^(2)n^(2)h^(2))/(2m_(1)^(2) m_(2)^(2) r^(2))`
`(n^(2)h^(2))/(2(m_(1)+m_(2))r^(2))`
`(2n^(2)h^(2))/((m_(1)+m_(2))r^(2))`
`((m_(1)+m_(2))n^(2)h^(2))/(2m_(1)m_(2)r^(2))`

SOLUTION :
`m_(1)r_(1)=m_(2)r_(2)`
`r_(1)+r_(2)=r`
`r_(1)=(m_(2)r)/(m_(1)+m_(2)), r_(2)=(m_(1)r)/(m_(1)+m_(2))`
`epsi=1/2 I omega^(2)`
`=1/2 (m_(1)r_(1)^(2)+m_(2)r_(2)^(2))omega^(2) ........(i)`
`mvr=(nh)/(2pi)=I omega`
`RARR omega=(nh)/(2pi I)`
`epsi=1/2 I. (n^(2)h^(2))/(4PI^(2)I^(2))`
`=(n^(2)h^(2))/(8pi^(2)) (1)/((m_(1)r_(1)^(2)+m_(2)r_(2)^(2)))`
`=(n^(2)h^(2))/(8pi^(2)) (1)/(m_(1)(m_(2)^(2)r^(2))/((m_(!)+m_(2))^(2))+m_(2) (m_(1)^(2)r^(2))/((m_(1)+m_(2))^(@)))`
`=(n^(2)h^(2))/(8pi^(2)r^(2)) ((m_(1)+m_(2))^(2))/(m_(1)m_(2)(m_(1)+m_(2)))=((m_(1)+m_(2))n^(2)h^(2))/(8pir^(2)m_(1)m_(2))`
`=((m_(1)+m_(2))n^(2)h^(2))/(2m_(1)m_(2)r^(2))`
Discussion
2721.

The existence of electromagnetic waves was theoretically predicted by

Answer»

Newton
Maxwell
Hertz
Huygens

Answer :B
Discussion
2722.

Consider the arrangement shown in figure, By some mechanism, the separation between the slits S_(3) and S_(4) can be changed. The intensity is measured at the pointP which is atthe common perpendicular bisector of S_(1)S_(2) and S_(3)S_(4). When z = (D lambda)/(2d), the intensity measured at P is I. Find this intensity when z is equal to 1) (D lambda)/(d), (2) (3Dlambda)/(2d) and (3) (2D lambda)/(d).

Answer»

O, I, 2I
I, O, 2I
2I, O, I
I, 2I, 3I

Answer :A
Discussion
2723.

The rate of cooling at 600 K, if surrounding tempearture is 300 K is R. The rate of cooling at 900 K is :

Answer»

`16/3R`
`2R`
`3R`
`2/3R`.

Solution :`Eprop(T^(4)-T_(0)^(4))`
`:.(E_(2))/(E_(1))=((900)^(4)-(300)^(4))/((600)^(4)-(300)^(4))`
`(E_(2))/(E_(1))=(9^(4)-3^(3))/(6^(4)-3^(4))=(16)/(3)rArrE_(2)=(16)/(3)E_(1)=(16)/(3)R`.
CORRECT CHOICE is (a).
Discussion
2724.

If the pressure, temperature and density of an ideal gas are denoted by P, T and rho, respectively, the velocity of sound in the gas is

Answer»

proportional to `sqrt(P)`, when T is CONSTANT
proportional to `sqrt(T)`
proportional to `sqrt(P)`, when `RHO` is constant
proportional to T.

Solution :Speed of the sound in the GAS is given by,
`v = sqrt((lambdaRT)/m) = sqrt((lambdaP)/rho)`
From this we conclude that velocity of sound in gas is proportional to `sqrt(T)` and also proportional to `sqrt(P)`, when `rho` is constant.
Discussion
2725.

Energy required to break one band in DNA is

Answer»

`~~1 E V`
`~~0.1 eV`
`~~0.01 eV`
`~~2.1 eV`

SOLUTION :The BOND strength in DNA is nearly 1 eV.
Discussion
2726.

White lightis passed through a doubleslitand interference pattern is observed on a screen 2.5 m away .Theseperationbetween the slits is 0.5 mm . The firstvioletand redfringers are formed 2.0 mm and 3.5 mm away from the centralwhite fringe .Calculatethe wavelengths of violet and thelight .

Answer»

400 nm , 650 nm
400 nm , 700 nm
350 nm , 200 nm
200 nm , 350 nm

Answer :B
Discussion
2727.

Draw a labelled diagram of a nuclear reactor and explain the functions of moderator, control rods and coolant.

Answer»



Solution :Nuclear reactor. Uncontrolled chain reaction causes a lot of damage. If the chain reaction is controlled in such a way that on the average, one neutron from each fission is left to excite further fission, the number of fissions occurring per second thus remains constant. In such cases, energy will not get out of control. Such a system in which the arrangement for absorption of desired number of neutrons is provided so that the chain reaction may proceed in a controlled manner is called nuclear reactor.
Construction. It consists of thick blocks of graphite in which long cylindrical holes have been drilled . Fissionable material is inserted through these holes.
Fuel. It consists of certain mass of fissionable material taken in the form of rod of few centimetres in diameter. It may consist of enriched uranium which is 3.5 % uranium -235 and 96.5% of uranium-238.
Moderator. To slow down the neutrons, they must suffer collision against atoms of material of moderator. Suitable material used as moderator are HEAVY water and graphite.

Controlling rods. Cadmium rods are used as controlling rods. The rods are inserted in the reactor and the chain reaction is controlled by careful adjustment of their length inside the carbon blocks. The movement of a cadmium rod by a little (say one cm distance) causes a significant difference in the performance of the reactor.
Working. Neutrons produced by the action of `alpha`- PARTICLE on polonium or beryllium are slowed down and are used initially to bring about fission of say `U^(235)` nuclei. The emitted neutrons are slowed down by the passage through the moderator to split further `U^(235)` nucleus. The chain reaction is said to be steady so that effective multiplication factor `K_(e)` is 1.
`K_(e)=("Rate of emission of neutrons")/("Rate of loss of neutrons")`
Some LOST neutrons are absorbed by `""_(92)U^(238)` present in enriched uranium which gives rise to `""_(94)U^(239)` as shown below:
`""_(0)n^(1)+""_(92)U^(238)rarr ""_(92)U^(239)rarr""_(-1)beta^(0)+""_(93)Np^(239)`
`""_(93)Np^(239) rarr ""_(-1)beta^(0)+""_(94)Pu^(239)`
`""_(94)Pu^(239)` is produced as a bye-product and can be used for fission purpose. India used `""_(94)Pu^(239)` in nuclear device which was exploded on 18th May 1974 and later on May 11 and 13, 1998 at Pokhran.
Uses. A nuclear reactor is used for generation of electricity, preparation of radio-isotopes. Most of energy set free is in the form of heat which through heat exchange is made to furnish steam to operate conventional turbined and electricgenerators.
Discussion
2728.

Draw a schematic diagram showing the nature of the alternating emf generated by the rotating coil in the magnetic field during one cycle.

Answer»

SOLUTION :
Discussion
2729.

A thermocouple has its junctions at 0^@ C and 100^@ C. It produces 0.022mV/K. Find the balancing length on a potentiometer wire of 10m length and resistance 10 Omegaconnected in series with a resistance box consisting of a resistance of 1990 Omega . Given emf of cell in the primary circuit as 2 volt

Answer»

110CM
220CM
330cm
440cm

Answer :B
Discussion
2730.

A stone of mass 0.005 kg is thrown vertically upwards. What is the direction and magnitude of net force on the stone during its upward motion ?

Answer»

0.049 N vertically downwards
9.8 N vertically downwards
0.49 N vertically UPWARDS
0.98 N vertically downwards.

Solution :When the stone is THROWN vertically upward then net force on the stone is F=mg actiing vertically downwards
`:. F=0.005xx9.8=0.49 N` vertically downwards.
Discussion
2731.

If c is the speed of electromagnetic waves in vacuum, its speed in a medium of dielectric constant K and relative permeability mu_r is

Answer»

`nu = 1/SQRT(mu_r K)`
`nu = c sqrt(mu_r K)`
`nu = c/sqrt(mu_r K)`
`nu = K/sqrt(mu_r c)`

Answer : `nu = mu_r/sqrt(CK)`.
Discussion
2732.

Explain mechanicalanalogy of LC oscillations by quantitative treament.

Answer»

Solution :i. The energy E remains constant for varying vaues of x and v. Differentiating E with respect to time, we get
`(dE)/(dt)=(1)/(2)(2v(dv)/(dt))+(1)/(2)k(2x(dx)/(dt))=0` or `m(d^(2)x)/(dt^(2))+kx=0" since "(dx)/(dt)=vand(dv)/(dt)=(d^(2)x)/(dt^(2))`
ii. This is the differential equation of the OSCILLATIONS of the spring-mass system. The general solution of eqution is of the from
`x(t)=X_(m)cos(omegat+phi)`
where `X_(m)` is the maximum value of `x(t),omega` the angular frequency and `phi` the phase constant.
iii. Similarly, the electromagnetic energy of the LC system is given by
`U=(1)/(2)LI^(2)+(1)/(2)((1)/(C))q^(2)="constant"`
Differentiating U with respect to time, we get
`(dU)/(dt)=(1)/(2)L(2I(di)/(dt))+(1)/(2C)(2q(dq)/(dt))=0`
`orL(d^(2)q)/(dt^(2))+(1)/(C)q=0""...(1)`
since `i=(dq)/(dt)and(di)/(dt)=(d^(2)q)/(dt2)`
iv. The general solution of equation (1) is of the form
`q(t)=Qmcos(omegat+phi)` v. where `Q_(m)` is the maximum value of q (t), `omega` the angular frequency and `phi` the phase consatnt.
Discussion
2733.

A 60V ,10W lamp is to be run on 100 V , 60 Hz ac mains , Calculate the inductance of the choke coil requiredto be connectedin seriesfor the bulb to work .

Answer»

Solution :GIVEN : P=10 W, V=60 V , `V_(RMS)` =100 VOLT
Current`I_(rms)=P//V=10//60=1//6A`
Resistance `R=V/I=60/(1//6)=60xx6=360 Omega`
IMPEDANCE `Z=V_(rms)/I_(rms)=100/(1//6)=600Omega`
`Z=sqrt(R^2+X_L^2) rArr L=sqrt(Z^2-R^2)/(2pif)=sqrt(600^2-360^2)/(2xx3.142xx60)`
L=1.273 H
Discussion
2734.

A current of 10A is passing through a long wire which has semicircular loop of the radius 20cm as shown in the figure. Magnetic field produced at the centre of the loop is

Answer»

`10pi mu T`
`5 PI mu T`
`4 pi mu T`
`2 pi mu T`

Answer :B
Discussion
2735.

_____ law deals with electrostatic force between charges.

Answer»

SOLUTION :Coulomb.s
Discussion
2736.

A voltmeter of resistance (2 x 10^4 Omega) reads 5V. To make it read 20V, the extra resistance required is

Answer»

`[4 X 10^4 OMEGA]` in PARALLEL
`[6 x 10^4 Omega]` in parallel
`[4 x 10^4 Omega]` in series
`[6 x 10^4 Omega]` in series

Answer :A
Discussion
2737.

What will be potential difference between the cathode and the grid voltage at which there will be a marked drop in the anode current in the Frank-Hertz experiment, if the tube is filled with atomic hydrogen?

Answer»


Solution :The first POTENTIAL jump TAKES place when the ELECTRON GOES over from the first to the second level:
`Deltaepsi=hcR(1/1^(2)-1/2^(2))`
Discussion
2738.

Name the factors which determines (i) frequency and (ii) intensity of light emitted by LED

Answer»

SOLUTION :[(i) BANDGAP (II) DOPING]
Discussion
2739.

Two identical positive charges are fixed on the y-axis at equal distances from the origin O . An particle with a negative charges starts on the x-axis at a large distance from O , moves along the x-axis , passes through O and moves far away from O. its acceleration a is taken as positive along its direction of motion . The particle's acceleration a is plotted against its x-coordinate. which of the following best represents the plot ?

Answer»




ANSWER :B
Discussion
2740.

A square shaped current carrying loop MNOP is placed near a straight long current carrying wire AB as shown in the figure. The wire and the loop lie in the same plane. If the loop experiences a net force F towards the wire, find the magnitude of the force on the side 'NO" of the loop.

Answer»

Solution :Force on the side .NO. of the loop due to current carrying WIRE is F = `(mu_(0))/(4pi). (2I_(1)I_(2))/(L+L) . L= (mu_(0))/(4pi).I_(1)I_(2)`
The force is REPULSIVE in NATURE (i.e., away from the wire)
Discussion
2741.

Statement-1:- The temperature dependence of resistance is usually given as R=R_(0)(1+alpha Deltat). The resistance of a wire changes from 100Omega to 150Omega when its temperature is increased from 27^(@)C to 227^(@)C. This implies that alpha=2.5xx10^(-3)//""^(@)C Statement- 2 :- R=R_(0)(1+alpha Deltat)is valid only when the change in the temperature DeltaT is small and DeltaR=(R-R_(0))lt lt R_(0)

Answer»

Statement-1 is TRUE, statement-2 is true, Statement-2 is the CORRECT EXPLANATION of statement-1.
Statement-1 is true, statement-2 is true, Statement-2 is not the correct explanation of statement-1 
Statement-1 is FALSE, Statement-2 is true 
Statement-1 is true, Statement-2 is false 

ANSWER :C
Discussion
2742.

In the displacement method, a convex lens is placed in between an object and a screen if the magnification in the two position are m_1 and m_2(m_1gtm_2) and the distance between the two positions of the lens is x, the focal length of the lens is

Answer»

`(X)/(m_1+m_2)`
`(x)/(m_1-m_2)`
`(x)/((m_1+m+2)^2)`
`(x)/((m_1-m_2)^2)`

ANSWER :A
Discussion
2743.

What is a magnetic dipole ?

Answer»

Solution :The MAGNETIC dipole consists of a north POLE and south pole of EQUAL strength and SEPARATED by a certain distance.
Discussion
2744.

(A): Transverse mechanical waves can not propagates in liquids and gases. (R): Liquids and gases flow when acted on by shearing stress, they can not sustain shear stress

Answer»

Both 'A' and 'R' are TRUE and 'R' is the CORRECT, explanation of 'A'.
Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
A' is true and 'R' is false
Both 'A' and 'R' are false

Answer :D
Discussion
2745.

A glass lens of refractive index 1.5 is placed in a trough of liquid. What must be the refractive index of the liquid in order to mark the lens disappear ?

Answer»

SOLUTION :REFRACTIVE INDEX of LIQUID should be 1.5.
Discussion
2746.

When we use zener diode as a voltage regulator, its connection ……. (i) forward bias (ii) reverse bias (iii) should parallel with load (iv) should series with load

Answer»

(i) and (II) are true
(ii) and (III) are true
only (i) is true
only (iv) is true

Answer :B
Discussion
2747.

In order to dcrease radioactive nuclei to one million of its initial number, number of half - lives required is

Answer»

20
40
40
10

Answer :A
Discussion
2748.

Assertion: If a heavy nucleus is split into two medium sized parts, each of new nucleus will have more binding energy per nucleon than original nucleus. Reason : Joining two light nuclei together to give a single nucleus of medium size means more binding energy per necleon in new nucleus.

Answer»

If both, ASSERTION and REASON are true and the Reason is the CORRECT explanation of the Assertion.
If both, Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
If Assertion is true but the Reason is false.
If both Assertion and Reason are false.

Solution :Both, assertion and reason are true, but the latter is not a correct explantion of the FORMER.
Discussion
2749.

A particle moving in a circular path with decreasing speed. Which of the following is correct?

Answer»

It will move in a spiral and finally reach the centre
Acceleration `veca` is towards the centre
Only direction of `vecL` is constant
`vecL` constant

Solution :If a particle MOVES in a circular PATH with decreasing speed, then only the direction of ROTATION REMAINS unchanged, so the direction of its angular momentum (L) will remain constant.
Discussion
2750.

The electric potential at a point near an isolated positive charge is

Answer»

Zero
Negative
Positiive
Infinite

Answer :C
Discussion