Saved Bookmarks
This section includes 7 InterviewSolutions, each offering curated multiple-choice questions to sharpen your Current Affairs knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Derive an equation showing the variation of magnetic field with distance. |
| Answer» SOLUTION :REFER TEXT | |
| 2. |
Explain the effect of temperature on surface tension? |
| Answer» Solution :The surface tension of a LIQUID decreases with the RISE of temperature. For small temperature difference, it decreases LINEARLY. Surface tension of a liquid is zero at it.s boiling point. Hence .,the boiling point is called as CRITICAL temperature of that liquid. | |
| 3. |
What are LC oscillations ? |
| Answer» Solution :When ever ENERGY is given to a circuit containing a pure inductor of INDUCTANCE L and a capacitor of capacitance C, the energy oscillates back and FORTH between the magnetic FIELD of the inductor and the electric field of the capacitor. Thus the electrical oscillations of definie frequency are generated. These oscillations are called LC oscillations. | |
| 4. |
Derivetheexpressionforenergystoredin acharged capacitor . |
|
Answer» Solution :Let.C.be thecapacitanceof a PARALLELPLATECAPACITOR. Bydefination` C =Q /V `. Bydefinationamountof workdoneto raisethe charge by. dq .is DW= Vdq . `i.e.,d W= (q) /(C ) dq ` Where .q.is theinstantaneousvalueof chargeonthe conductor . Totalworkin chargingthe capacitorisgivenby, ` W = int _(q=0)^(q=Q) dW ` `i.e.,W = int _(q=0) ^(q=Q) ((q)/(C ))dq ` `i.e, W =(1 )/(C ) [(q^(2))/(2)]_(0)^(Q)` Or ` W=(1)/(2) (Q^(2))/(C )` , AMOUNTOF workdoneis storedin theformof energy . THEREFORE` E= (1)/(2) ((Q^(2))/(C ))` Using`Q=CV , E =(1)/(2) CV ^(2)` , where.V.is themaximumvoltagesuppliedto a capacitor . |
|
| 5. |
Only the stars near the horizon twinkle while those overhead do not twinkle, why? |
| Answer» Solution :Light from the stars near the horizon REACHES the earth obliquely through the atmosphere. Its path CHANGES due to refraction. Frequent atmospheric disturbances changes the path of ligh and cause TWINKLING of stars. Light from the stars OVERHEAD reaches the earth normally. It does not SUFFER refraction. There is no change in it.s path. hence, there is no twinkling effect. | |
| 6. |
For previous objective, which of the following graph is correct |
|
Answer»
|
|
| 7. |
A solid sphere of mass M, radius R and having moment of inertia about an axis passing through the centre of mass as J, is recast into a disc of thickness t, whose moment of inertia about an axis passing through its edge and perpendicular to its plane remains J. Then, radius of the disc will be |
|
Answer» `(2R)/(sqrt(15))` Moment of inertia of circular disc of radius r and mass M about an axis passing through the centre of mass and perpendicular to its plane `=1/2Mr^(2)` `therefore` Using theorem of PARALLEL AXES, moment of inertia of disc about its edge is `I.=1/2Mr^(2)+Mr^(2)=3/2Mr^(2)` GivenI=I. or, `2/5MR^(2)=3/2Mr^(2)` or `r^(2)=4/15R^(2)` or, `r=(2r)/(sqrt(15))` |
|
| 8. |
At what speed must the rotor of Lammert's machine rotate for gas molecules with velocities of 700 m/s to pass through the slits? What velocity spread will be recorded in the experiment? Take the distance between the disks to be 40 cm, the angle between the slits to be 20^@ and the angular width of the slit to be 2^@. Estimate the error in the experiment. |
|
Answer» |
|
| 9. |
A solid sphere starts from rest at the top of an incline of height h and length l, and moves down. The force of friction between the sphere and the incline is F. This is insufficient to prevent slipping. The kinetic energy of the sphere at the bottom of the incline is W. |
|
Answer» The WORK DONE against the force of FRICTION is Fl. |
|
| 10. |
How much is the self-induced voltage across a 4 H inductances, produced by a current change of 12 As^(-1) ? |
|
Answer» |
|
| 11. |
Why are infrared rays often called heat waves? |
| Answer» SOLUTION :x-RAYS/`GAMMA` rays. RANGE `10^18` HZ to `10^22` Hz | |
| 12. |
In YDSE, the phase difference between two coherent sources is pi//3 constant. The intensity at a point which is at equal distance from the source is (I_(0) is maximum intensity) |
|
Answer» `(sqrt(3))/(2)I_(0)` |
|
| 13. |
The power of a motor is 200W. If the unit of length is halved, that of mass is doubled and that of time is aiso doubled, then the power of the motor in the new system is |
|
Answer» 3200 W |
|
| 14. |
लकादीव, मीनिकाय तथा एमीनदीव को 1973 से किस नाम से जाना जाता है? |
|
Answer» अंडमान द्वीप |
|
| 15. |
A body is pushed up on a rough inclined plane making an angle 30^@ to the horizontal. If its time of ascent on the plane is half the time of its descent, find coefficient of friction between the body and the incined plane. |
|
Answer» `(SQRT3)/(5)` |
|
| 16. |
There are two indetical capacitor , the first one is uncharged and filled with dielectric of constant K while the otherone is charged to potential v having air between its plates, if two capacitors are joined end to end, the common potential will be |
|
Answer» `(V)/(K - 1)` |
|
| 17. |
Describe construction, working and use of the solar cell. |
|
Answer» Solution :A solar cell is basically a p-n junction which generates emf when solar radiation falls on the p-n junction. Sunlight is not always REQUIRED for solar cells but the energy of the photon of the light which is greater than the band gap energy of semiconductor can also produce the photo VOLTAGE. The principle of the working of photodiode and solar cell are same and it works on the principle of photovoltaic effect but doesn.t require external battery in solar cell. If you need more power than Sunlight, the area of the junction has to be very large. The The diagram depicts the appearance of the solar cell and its cross section.  A p - Si wafer of about 300 `mu`m is taken over which a thin layer `(~0.3mum)`of n - Si is GROWN on one side by diffusion process. The other side of `p-Si` is coatedwith a metal (back contact). On the TOP of `n-Si` layer, metal finger electrode, (or metallic grid) is deposited. This acts as a front contact. The metallic grid occupies only a very small fraction of the cell area `(lt 15%)` so that light can be incident on the cell from the top. The generation of emf by a solar cell, when light falls on it is due to the following three basic processes. (In order to produce an emf, a pair of electron hole must be generated and must gather). (1) generation of e-h pairs due to light (with`hv gt E_(g)`) close to the junction. (2) Separation of electrons and holes due to electric field of the depletion region. Electrons are swept to n-side and holes to -sides. (3) Electrons reaching the n-side are collected by the front contactand holes reaching p-side are collected by the back contact. Thus, p-side becomes positive and n-side becomes negative giving rise to photovoltage. When an external load is connected as shown in the figure (a) a photocurrent `I_(L)` flows through the load due to incident light on solar cell.  `I to V` characteristics of solar cell is drawn in the fourth quadrant of the coordinate axes. This is because a solar cell does not draw current but supplies the same to the load.  Uses of solar cells: (1) The power electronic devices in satellites and space vehicles. (2) As a power suupply in calculator, electronic watch and camera and (3) MANY solar cells have a series or parallel connections that can provide the required voltage and current such a solar cell connection is called a solar panel. Solar panels are used to obtain electrical energy in a satellite with the use of such panels, the secondary electric cell can be obtained during the night. |
|
| 18. |
When electric field (vecE) is applied on the ends of a conductor, the free electrons starts moving in direction |
|
Answer» SIMILAR to `vecE` |
|
| 19. |
(a) A proton is moving in a magnetic field. The field overline(B) is into the plane of the page. The velocity vector, overline(v) lies in the plane of the page. Perpendicular to overline(B). Describe the motion of proton. (b) In part (a) : if the radius fo the circle is 0.5 m and the magnitude of the magnetic field is 1.2 wbm^(2). find the frequency of revolution and the kinetic energy of the proton. Charge of the proton = 1.60 xx 10^(-19) C. Mass of the proton = 1.67 xx 10^(-27) kg. |
|
Answer» |
|
| 20. |
If a soap bubble be electrified, will its shape be changed? If so, how will the potential of the bubble change? |
|
Answer» Solution :A soap bubble is considered as a spherical conductor. When it is a electrified, the charge distribution on its surface will have a REPELLING EFFECT. HENCE, the radius of the bubble INCREASES. Capacitance of a spherical conductor varies with its radius, but it still remains spherical. So, the capacitance of the charged bubble increases. The POTENTIAL, `V= (" charge ")/(" capacitance ")`, if the charge constant, potential of the bubble will decrease. |
|
| 21. |
A nail is fixed up perpendicularly at the centre of a circular wooden plate. Keeping the nail at bottom, the circular plate is made of float in water. What should be the maximum ratio of the radius of the plate and length of the nail so that the nail wil be out of vision? Refractive index of water = (4)/(3). |
|
Answer» Solution :AB is the circular wooden plate and CD is the nail. Suppose, RADIUS of the plate = r and the length of the nail = h [Fig. 2.30]. Since the nail is not seen from air, the angle of incidence of the RAY DA will be GREATER than `theta_(c)` and the ray will be totally reflected. `"We know", sintheta_(c) = (1)/(a^(mu)w) = (3)/(4)` `therefore "" costheta_(c) = sqrt(1-(9)/(16)) = sqrt(7)/(4) and tantheta_(c) = ((3)/(4))/((sqrt7)/(4)) = (3)/(sqrt7)` `or, "" (r)/(h) = (3)/(sqrt7)` This is the required ratio. 
|
|
| 22. |
Two capacitors of capacitance 600 pF and 900 pF are connected in series across a 200 V supply. Calculate (i) the effective capacitance of the combination, (ii) the pd across each capacitor and (iii) the total charge stored in the system. |
Answer» Solution : `C_(eff) = (C_1C_2)/(C_1 + C_2)` ` = (600 xx 900)/(600 + 900) = 540000/1500` `C_(eff) = 360 pF` ` Q = CV = 360 xx 200` `Q = 72 NC` `V_1 = (Q)/(C_1) = 120 V` `V_1 = (Q)/(C_2) = 80 V` |
|
| 23. |
Frictional force increases when surfaces in contact are made very very smooth. This is because |
|
Answer» of MOLECULAR force |
|
| 24. |
Two capacitors C_(1) = 2mu F and C_(2) = 1 muF are charged to same potential V = 100 V, but with opposite polarity as shown in the figure. The switches S_(1) and S_(2) are closed. The ratio of final energy to the initial energy of the system is |
| Answer» ANSWER :C | |
| 25. |
A rectangular loop of wire is moved within the region of a uniform magnetic field acting perpendicular to its plane. What is the direction and magnitude of current induced in it ? |
| Answer» Solution :If loop MOVES WITHIN the region of uniform MAGNETIC FIELD no current will be induced in the loop. HENCE no direction. | |
| 26. |
विश्व मे जल के कुल आयतन का कितने प्रतिशत भाग महासागरों मे पाया जाता है - |
|
Answer» 0.965 |
|
| 27. |
Out of the following which one is not a possibleenergy for a photon to be emitted by hydrogenatom according to Bohr's atomic model? |
|
Answer» `13.6` EV |
|
| 28. |
Statement - (A): A steady current is flowing in a cylindrical conductor, the electric field with in the conductor is not zero. Statement-(B):Electrons in a conductor have no motion in the absence of a potential difference across it. |
|
Answer» Both A and B are TRUE |
|
| 29. |
Colours of soap film in sun light is due to |
|
Answer» dispersion |
|
| 30. |
किसी गतिशील वस्तु का वेग-समय ग्राफ चित्र में दर्शाया गया है। उस समयान्तराल में, जिसमे वस्तुका त्वरण तथा मंदन अशून्य रहता है, कुल विस्थापन हे, |
|
Answer» 60m |
|
| 31. |
An electric bulb rated 220-100W.The power consumed by it when operated on 110V will be |
|
Answer» 25 W |
|
| 32. |
In photoelectric effect, the KE of electrons emitted from the metal surface depends upon |
|
Answer» INTENSITY of LIGHT |
|
| 33. |
Uncertainty in position of electron is 10^(-10) m. uncertainty in its momentum will be…….kgms^(-1).(h=6.62xx10^(-34) J-s) |
|
Answer» `1.05xx10^(-24)` `Deltax.DELTAP=(h)/(lpi)` `Deltap=(h)/(2piDeltax)=(6.62xx10^(-34))/(2xx3.14xx10^(-10))` `therefore Deltap=1.05xx10^(-24)kg MS^(-1)` |
|
| 34. |
MnO shows |
|
Answer» Paramagnetism |
|
| 35. |
The period of revolution of planet  around the sun is 8 times that of B. The distance of A from the sun is how many times greater than that of B from the Sun- |
|
Answer» a)223 days |
|
| 36. |
Draw intensity pattern of light in an interference of light waves. |
Answer» SOLUTION :
|
|
| 37. |
The core and the armature of an electromagnet with dimensions in millimeters as shown in Fig. 30.16 have been manufactured from a ferromagnetic material whose properties have been described in Problem 29.10. What is the force with which the core attracts the armature, if the material has been magnetized to saturation? What force will remain active after the current is switched off? |
|
Answer» We have `F_("sat")=B_(x)^2 "at" S//mu_(0)` in case of saturation magnetization and `F_(r)=-B_(r)^2 S//mu_(0)` in the case of residual magnetization. The values of `B_("sat") and B_(r)` are presented in the table following Problem 29.10 (see alsu fig. 29.10) |
|
| 38. |
The work done in increasing the P.D. across the plates of a capacitor from 4V to 6Vwork done in increasing the P.D. from 6V to 8V is |
| Answer» Answer :C | |
| 39. |
A particle moves along a horizontal circle with constant speed. If 'a' is its acceleration and 'E' is its kinetic energy A) a is constantB) E is constant C) a is variableD) E is variable |
|
Answer» A & B are CORRECT |
|
| 40. |
If the amplitude ratio of two source producing interference is 3.5 ,the ratio of intensities of maxima and minima is |
|
Answer» `25:16` |
|
| 41. |
A metal rod of length l cuts across a unifrom magnetic field B with a velocity v. If the resistance of the circuit of which the rod forms a part is r, then the force required to move the rod is |
|
Answer» a. `(B^2l^2)/(R)` |
|
| 42. |
In an LCR series a.c. circuit, the voltage across each of the components L, C and R is 50 V. The voltage across the LC combination will be |
|
Answer» 50 V |
|
| 43. |
The ratio of the energy of a photon with lambda = 150 nm to that with lambda = 300nm is |
| Answer» Solution :`(E_(1))/(E_(2)) = (lambda_(2))/(lambda_(1)) = (300)/(150) = 2` | |
| 44. |
The graph shown part of variation of v with change in u for a concave mirror. Points plotted above the point P on the curve are for values of v |
|
Answer» SMALLER than f  If we take ANOTHER pointQ just above P, then `vgt2f`. |
|
| 45. |
If waves of light having intensity I_(1) and I_(2) passes through any region in the same time in the same direction, what will be sum of maximum and minimum intensity ? |
|
Answer» `I_(1)+I_(2)` `I_("max")=I_(1)+I_(2)+2 sqrt(I_(1)I_(2))` For maximum intensity `cos phi=-1` `I_(MIN)=I_(1)+I_(2)-2 sqrt(I_(1)I_(2))` Now `I_("max")+I_("min")` `=I_(1)+I_(2)+2 sqrt(I_(1)I_(2))+I_(1)+I_(2)-2 sqrt(I_(1)I_(2))` `=2(I_(1)+I_(2))` |
|
| 46. |
For a capacitor the distane between two plates is 4x and the electric field between them is E_(0). Now a dielectric slab having dielectric constant 3 and thickkness x is placed between them in contact with one plate. In this condition what is the p.d. between its two plates ? |
|
Answer» `(10 E_(0)x)/(3)` `= (E_(0))/(3) x+ 3E_(0)x = (E_(0)x+9E_(0)x)/(3) = (10E_(0)x)/(3)` |
|
| 47. |
Anunstable high-energy particle enters a detector and leaves a track of length 0.856 mm before it decays. Its speed relative to the detector was 0.992c. What is its proper lifetime? That is, how long would the particle have lasted before decay had it been at rest with respect to the detector? |
|
Answer» |
|
| 48. |
Two charged particles having charges 1muC and -1muC and of mass 50 gm each are held at rest while their separation is 2 m. Find the speed of the particles when their separation is 1 m. |
|
Answer» `(1)/(5) m//s` |
|
| 49. |
Ratio of power factor in two A.C. circuits (i) containing only resistance and (ii) containing only inductor is ……. |
|
Answer» Solution :(i)Only resistor : tan `delta_1=(X_L-X_C)/R=0` `(because X_L=X_C=0)` `therefore delta_1=0 RARR cos delta_1=1`….(1) (II) Only inductor : `tan delta_2=(X_L-X_C)/R=(X_L-0)/0 =oo (because X_C=R=0)` `therefore delta_2=pi/2` RAD `therefore cosdelta_2=0`....(2) From (1) and (2) `(cosdelta_1)/(cos delta_2)=1/0 = oo` |
|
| 50. |
A bullet of mass m moving with a horizontal velocity u strikes a stationary block of mass M suspended by a string of length L. If the bullet gets embedded, to what maximum angle, with vertical, the block would risc ? |
|
Answer» `cos^(-1)[(m^(2)v^(2))/(2GL(M+m)^(2))]` By law of conservation of momentum mv=(M+m) V where V is the velocity of combination.By conservation of ENERGY `1/2(m+M)V^2=(M+m)gh` or `V^2=2gh`  Squaring the first eqn. `V^2=(m^2v^2)/((m+m)^2)`.THUS putting for `V^2` and .h. `2gL(1-cos theta)=(m^2v^2)/((M+m)^2)` or `theta=cos^(-1)[1-(m^2v^2)/(2gL(M+m)^2)]` |
|
