Question Bank for High School Science/Physics/DPMT2005

Questions

1. S.I. unit of magnetic flux is (a) tesla (b) oersted (c) weber (d) gauss.

2. A body of mass m is moving towards east and another body of equal mass is moving towards north. If after collision both stick together, their speed after collision would be (a) v (b) v/2 (c) 72 v (d) v/72

3. A body of mass 1 kg is moving in a vertical circular path of radius 1 m. The difference between the kinetic energies at its highest and lowest position is (a) 20 J (b) 10 J (c) 475 J (d) 10(75-1) J

4. Across each of two capacitors of capacitance 1 |iF and 4 [J.F, a potential difference of 10 V is applied. Then positive plate of one is connected to the negative plate of the other, and negative plate of one is connected to the positive plate of the other. After contact, (a) charge on each is zero (b) charge on each is same but non-zero (c) charge on each is different but non-zero (d) none of these.

5. Magnification of a compound microscope is 30. Focal length of eye piece is 5 cm and the image is formed at a distance of distinct vision of 25 cm. The magnification of the objective lens is (a) 6 (b) 5 (c) 7.5 (d) 10.

6. Kirchoff's law of junction, 2/ = 0, is based on (a) conservation of energy (b) conservation of charge (c) conservation of energy as well as charge (d) conservation of momentum.

7. Calculate the amount of heat (in calories) required to convert 5 g of ice at 0°C to steam at 100°C . (a) 3100 (b) 3200 (c) 3600 (d) 4200.

8. A transverse wave is expressed as : y = y0s'm2nft. For what value of A,, when maximum particle velocity is equal to 4 times the wave velocity? (a) y0n/2 (b) 2y0n (c) y0n (d) y0n/4.

9. Two bodies are thrown up at angles of 45° and 60°, respectively, with the horizontal. If both bodies attain same vertical height, then the ratio of velocities with which these are thrown is (a) 7273 (b) 2/73 ( C ) 7 5 7 2 (d) 7 3 / 2 •

10. Charges 40, q and 0 are placed along x-axis at positions x-Q,x = U2 and x = I, respectively. Find the value of q so that force on charge 0 is zero. (a) Q (b) 0/2 (c) - 0 / 2 (d) - 0.

11. A ray fall on a prism ABC (AB - BC) and traval as shown in figure. The least value of refractive index of material of the prism, should be (a) 1.5 (b) 72 (c) 1.33 (d) 73

12. Escape velocity from a planet is v„. If its mass is increased to 8 times and its radius is increased to 2 times, then the new escape velocity would be (a) v„ (b) 72vc (c) 2v„ (d) 272vc

13. A body takes time t to reach the bottom of an inclined plane of angle 8 with the horizontal. If the plane is made rough, time taken now is 21. The coefficient of friction of the rough surface is

(a) -tanG (c) -jtanS (b) -tan 9 (d) itanG

14. Two small charged spheres A and B have charges 10 jxC and 40 jiC respectively, and are held at a separation of 90 cm from each other. At what distance from A, electric intensity would be zero? (a) 22.5 cm (b) 18 cm (c) 36 cm (d) 30 cm.

15. 50 tuning forks are arranged in increasing order of their frequencies such that each gives 4 beats/sec with its previous tuning fork. If the frequency of the last fork is octave of the first, then the frequency of the first tuning fork is (a) 200 Hz (b) 204 Hz (c) 196 Hz (d) none of these.

16. In a cyclotron, if a deuteron can gain an energy of 40 MeV, then a proton can gain an energy of (a) 40 MeV (b) 80 MeV (c) 20 MeV (d) 60 MeV.

17. Graph between velocity and displacement of a particle, executing SHM is (a) a straight line (b) a parabola (c) a hyperbola (d) an ellipse.

18. In the nuclear reaction, 180 v 72 A - - > y - -P -Y the atomic mass and number of P are, respectively (a) 170,69 (b) 172,69 (c) 172, 70 (d) 170, 70.

19. A radioactive substance has activity 64 times higher than the required normal level. If T]/2 = 2 hours, then the time, after which it should be possible to work with it, is (a) 16 hrs. (b) 6 hrs. (c) 10 hrs. (d) 12 hrs.

20. An electron, moving in a uniform magnetic field of induction of intensity B, has its radius directly proportional to (a) its charge (b) magnetic field (c) speed (d) none of these.

21. The apparent frequency in Doppler's effect does not depend upon (a) speed of the observer (b) distance between observer and source (c) speed of the source (d) frequency from the source.

22. Two simple pendulums whose lengths are 100 cm and 121 cm are suspended side by side. Their bobs are pulled together and then released. After how many minimum oscillations of the longer pendulum, will the two be in phase again? (a) 11 (b) 10 (c) 21 (d) 20.

23. If percentage change in current through a resistor is 1%, then the change in power through it would be (a) 1% (b) 2% (c) 1.7% (d) 0.5%

24. 3 identical bulbs are connected in series and these together dissipate a power P. If now the bulbs are connected in parallel, then the power dissipated will be (a) PI3 (b) 3P (c) 9P (d) PI9.

25. Acceleration due to gravity (a) decreases from equator to poles (b) decreases from poles to equator (c) is maximum at the centre of the earth (d) is maximum at the equator.

Solutions

1. (c)

2. (d) : From the principle of conservation of linear momentum, mvi + mvj = 2 mv' | 2mv' | = m | vi + vj | , ~Jlv v or, 2 mv' = m\v2 + v2 72'

3. (a) : Difference in kinetic energy = 2mgr = 2 x 1 x 10 x 1 = 20 J.

4. (c): Stored charge on capacitor becomes zero only when it is discharged through resistance or when two capacitors of equal capacitance are charged and then connected to opposite terminals. Here the capacitances are different.

5. (c) : M.P. of compound microscope = m„ x me r u v D where me= — = — = u„ u„ 1 + D_ fe 30 = m„ x 6 => m„ = 5.

6. (b) : Kirchoff's law of junction is based on the law of conservation of charges i.e. on the fact that charges do not remain accumulated at a junction of a circuit i.e. a junction of a circuit cannot act as source or sink of charges. Total rate of incoming charges is equal to the total rate of outgoing charges.

7. (c) : Heat required = heat require to melt ice to water of 0°C + heat require to boil water to 100°C + heat require to make steam at 100°C = mL, + msAt + mLs = 5 x 80 + 5 x l x 100 + 5 x 540 = 400 + 500 + 2700 = 3600 cal.

8. (a) : As given in question, maximum particle velocity = 4 * wave velocity JW° = X 4xoo k y0n/2.

9. (c) : Vertical height «2sin26 2g where u is initial velocity of the body. sin2 45 _ u2 2 sin2 60 2g ~ 2g _ sin2 60 uj _ -v/3/2 ^ u2 2~ sin2 45 u2 l/y/2

10. (d) : The total force on Q Qq , 4QxQ 4 O 4TO0(//2r Qq 47ts0/" • = 0 //2 4 QxQ 4ti£0(/ /4) 4TT£0/

11. (b) : As AB = BC, Z A = Z C = 45° At each reflection, Zr = 45° = i e , critical angle 1 sin;',. sin 45° • = ^2.

12. (c) : Escape velocity 2, 27? V 2 GM 2GW) 2GM R R = 2v„.

13. (a): When body moves on frictionless surface then 1 ~> d — —gsiti&t When body moves on rough inclined d = -ig(sin6-ficos0)(2O2 1 • •> 1 —:g(sin0-(J.cos9)(2<) • = —gsin0< sin0-ficos0 = p.cos0 = sinQsin0 4 sinG -sin9 4 4

14. (d): Let at a distance ^ x the total electric intensity ' > H = —tan8. 4 £ = 0 X - 90-x -X 1A qB 4TV£QX 4ne0(90-x) - = 0 ,-6 x (90-x)2 • (90 - x2) = 4x2 90 - x = 2x => 3x = 90 => x = 30 cm.

15. (c) : As given, u2 = u + 4 Similarly, «, = « + ( / i - l )M From given condition, 1),, = 2v => u + (50 - 1) x 4 = 2v = j2mE •u = 196 Hz.

16. (b) : R = - qB j2mE = RqB As R is a constant for the cyclotron (it is cyclotron radius) and q for the deuteron and proton are the same, RqB is a constant. ••• V2mp'Ep =4lmd-Ed => J2mp-Ep =^2(2 mp)Ed

. Ep = 2Ed = 2 x 40 = 80 MeV.

17. (d) : In simple harmonic motion, y = a sinottf, v = acocosoo/ From this, we have V2 V 2 - y + - - =1, which is equation of ellipse. a a (0

18. (b) : '7 8 2°Z- . 176y 5He ^ 176 -7 _L „ 0 > 71 Z + e _! -> + jHe p ' v 172 69 ^ + energy

19. (d) : 4 . 1 - 1J - - nTm = T => T= 6 x 2 = 12 hr.

20. (c) : When electron moves in a magnetic field, mv.2 = qvB r qB

21. (b): Apparent frequency in Doppler effect depends on frequency of source, direction and velocity of source and observer. 7

22. (b) : T = 2nij- For / = 121 cm and / = 100 cm («)11 = (« + 1)10. n = 10.

23. (b) : Power = PR A P „ Af A R — = 2 y + — . AP - 2 x 1% + 0 = 2%.

24. (c) : When bulbs are connected in series, pJ—-RV—' 3 R When bulbs are connected in parallel, P' = - V2X3 = 3x3P = 9P. R" R

25. (b) : At poles, the effect of rotation is negligible because of which g is maximum while at equator the effect of rotation on g is the maximum. Therefore, value of g is minimum. Thus as we go from pole to equator acceleration due to gravity decreases.