Objective physics questions Fully Solved with answers

1. The dimensional formula for Plancks constant and angular momentum is:

(a) [ML²T²] and [MLT^-1]

(b) [ML²T^-1] and [ML²T^-1]

(c) [ML³T¹] and [ML²T^-2]

(d) [MLT^-1] and [MLT^-2] ‘

Ans. (b)

2. A body of mass m moving with velocity u collides with a stationary body of mass 2 m. The speed of the system after collision, is

(a) 3u

(b) u/3

(c) 2u

(d) u/4

Ans. (b)

3. A wet open umbrella is held vertical and it whirled about the handle at a uniform rate of 21 revolutions in 44 s. If the rim of the umbrella is a circle of 1. m in dimeter and the height of the rim above the flour is 4.9 m, the locus of the drop is a circle of radius

(a)√2.5 m

(b) 1 m

(c) 3 m

(d) 1.5 m

Ans. (a)

4. The moment of inertia of a body about a given axis is 1.2 kg- m². To produce a rotational kinetic energy of 1500 J an angular acceleration of 25 rad /s²must be applied for:

(a) 8.5 s

(b) 5s

(c) 2 s

(d) 1 s

Ans. (c)

5. An earth satellites S has an orbit radius which is 4 times that of communication satellite C. The period of revolution of S will be:

(a) 32 day

(b) 18 days

(c) 8 days

(d) 9 days

Ans. (c)

6. n small balls, each of mass m impinge elastically each second on a surface with a velocity u, then the force experienced by the surface in one second, will be

(a) 4 mnu

(b) 2 mnu

(C) 1.5mnu

(d) 0.8mnu

Ans. (b)

7. An object of mass 40 kg and having a velocity 4 m/s collides with another object     (m = 60 kg)having velocity 2 m/s. The collision is perfectly inelastic. The loss in energy is

(a) 110 J

(b) 48 J

(c) 392 J

(d) 440 J

Ans. (b)

8. Dimensions of surface tension are:

(a) [M²L²T²]

(b) [M²LT²]

(c) [MT²]

(d) [MLT²]

Ans. (c)

9. An iron rod of length 2 m and area of cross-section 50 mm2 stretches by 0.5 mm, when a mass of 250 kg is hung from its lower end. The Young’s modulus of iron rod is:

(a) 19.6×10²⁰N/m²

(b) 19.6×10¹⁸N/m²

(c) 19.6 xI0¹⁵ N/m²

(d) 19.6 x10¹⁰N/m²

Ans. (d)

10. 16 cm³ of water flows per second through a capillary tube of radius a cm and of length land when connected a pressure head of H cm of water. If a tube of same length and radius a/2 cm is connected to the same pressure head the quantity of water flowing through the tube per second is

(a) 8cm³

(b) 1cm³

(c) 16 cm³

(d) 4 cm³

Ans. (b)

11. Pressure inside two soap bubbles are 1.01 and 1.03 atm. Ratio between their volumes is:

(a) 27:1

(b) 3:1

(c) 127:101

(d) None of these

Ans. (a)

12. A stationary object at 4°C and weighing 3.5 kg falls from a height of 2000 m on a snow mountain at 0°C. If the temperature of the object just before hitting the snow is 0°C and the object comes to rest immediately (g = 10 rn/s² and latent heat of ice = 3.5 x 10⁵ J/s) , then the object will melt:

(a) 2 kg of ice

(c) 20 g ice

(b) 200 g of ice

(d) 2 g ice

Ans. (b)

13. A Carnot enging works between temperatures 727°C and 27° C. The efficiency of the engine is:

(a) 70%

(b) 30%

(c) 0%

(d) 10%

Ans. (a)

14. A sphere at temperature 600 K is placed in environment of temperature 200 K. Its cooling rate is H. If the temperature is reduced to 400 K, then the cooling in same environment will be:

(a) H/16

(b) (9/27) H

(c) (16/3) H

(d) (3/16) H

Ans. (d)

15. An ideal gas at 27° C is compressed adiabatically to 8/27 of its original volume if

y = 5/3, then rise in temperature is:

(a) 405 K

(b) 225K

(c) 375 K

(d) 450 K

Ans. (c)

16. The root means square velocity of the molecules in a sample of helium 5/7th that of the molecules in a sample of hydrogen at 0°C. Then, the temperature of helium sample is about

(a) 100° C

(b) 273°C

(c) OK

(d) 0°C

Ans. (d)

17. The displacement of the particle from its mean position (in meter) varies with time (in second) according to the equation: y = 0.2 sin (l0∏t + L57∏) cos (l0∏t + 1.5∏). The motion of the particle is

(a) Along a circular path

(b) Simple harmonic motion with time period 0.1 S

(c) No simple harmonic motion

(d) Simple harmonic motion with time period 0.2s

Ans. (b)

18. Light of frequency 8 x 10¹⁵ Hz is incident on a substance of photoelectric work function 6.125 eV. The maximum kinetic energy of the emitted photoelectrons will be

(a) 39 eV

(b) 27 eV

(c) 54eV

(d) 13.5eV

Ans. (b)

19. A cylindrical tube, open at both ends has a fundamental frequency f in air. The tube dipped vertically in water, so that half of it is in water, the fundamental frequency of the air column is now:

(a) 2f

(b) f

(c) 3f/4

(d) f/2

Ans. (b)

20. The distance between two points difference in phase by 60° on a wave having a wave velocity 360 m/s and frequency 500 Hz is:

(a) 0.36m

(b) 0.12m

(c) 0.18m

(d) 0.72m

Ans. (b)

21. The heat generated in a circuit is dependent upon the resistance, current and time for which the current is flown. If the error in measuring. The above are 1%, 2% and 1% respectively. The maximum error in measuring the heat is

(a) 8%

(b) 6%

(c) 18%

(d) 12%

Ans. (b)

22. A particle having charge 100 times that of an electron is revolving in a circular path of radius 0.8 m with one rotation per second. The magnetic field produced at the centre will be

(a) 10^-17 µ₀

(b) 10^-11 µ₀

(c) 10^-7 µ₀

(d) 10^-3 µ₀

Ans. (a)

23. The energy of an X-ray photon is 2 keV, then its frequency will be:

(a) 3.2 x l0^-6 per sec

(b) 5×10¹⁷per sec

(c) 2 x 10¹⁷ per sec

(d) 2 x l0¹⁸ per sec

Ans. (b)

24. A refracting angle of a prism is A and the refractive index of the prism is cot (A/2) Then, angle of minimum deviation is:

(a) 180° – 2A

(b) 90° – A

(c) 180° + 2A

(d) 180° – 3A

Ans. (a)

25. If the critical angle for total internal reflection from medium to vacuum is 30°. The velocity in the medium will be:

(a) √3 x 10⁸ m/s

(b) 6 x 10⁸ m/s

(c) 1.5 x 10⁸ m/s

(d) 3 x 10⁸ m/s

Ans. (c)

26. The length of an astronomical telescope adjusted for parallel light is 100 cm. If the magnification of the telescope is 19. The focal length of two lenses, i.e., objective and eye piece are

(a) 76 cm and 4 cm

(b) 95 cm and 5 cm

(c) 85 cm and 15 cm

(d) 82 cm and 18 cm

Ans. (b)

27. Doubly ionised helium atoms and hydrogen ions are accelerated from rest through the same potential drop. The ratio of the final velocities of helium and the hydrogen ions are:

(a) 1/2

(b) 1/√2

(c)√2

(d) 2

Ans. (b)

28. In a transformer, the number of turns of primary coil and secondary coil are 5 and 4 respectively. If 220 V is applied on the primary coil, then the ratio of primary current to the secondary current will be

(a) 9:5

(b) 5:9

(c) 5:4

(d) 4:5

Ans. (d)

29. If the distance between parallel plates of a capacitor is halved and dielectric constant is doubled then the capacitance will

(a) Remain the same

(b) Increase 4 times

(c) Increase 2 times

(d) Decrease 2 times

Ans. (b)

30. In a nuclear fission, 0.1% mass is converted into energy. The energy released by the fission of 1 kg mass will be:

(a) 9 x 10¹⁹ J

(b) 9 x 10¹⁷ J

(c) 9 xl0¹⁶ J

(d) 9 xl0¹³ J

Ans. (d)

31. The energy of hydrogen atom in the nth orbit is E_n, then the energy in the nth orbit of single ionised helium atom is:

(a) E_n/2

(b) 2E_n

(c) 4E_n

(d) E_n/4

Ans. (c)

32. Force between two identical bar magnets whose centres r metre apart is 4.8 N when their axis are in the same line. If the separation is increased to 2 r metres, the force between them is reduced to

(a) 0.3N

(b) 0.6N

(c) 2.4N

(d) 1.2N

Ans. (a)

33. An air capacitor of capacity C = 10 µF is connected to a constant voltage battery of 12 V. Now, the space between the plates is filled with a liquid of dielectric constant 5. The additional charge that flows now from battery to the capacitor is

(a) 24 µC

(b) 480 µC

(c) 600 µC

(d) 120 µC

Ans. (b)

34. Pure silicon at 300 K has equal electrons n_e and holes h concentration of                  1.5 x 10¹⁶/m3. Doping by indium increases number of holes h to 4.5 x 10²²/m3 then n_e ‘doped in silicon will be:

(a) 3.0x 10^-19/m³

(b) 5×10⁹/m³

(c) 4.5×10²²/m³

(d) 1.5xl0¹⁶/m³

Ans. (b)

35. In an atom bomb the reaction which occurs is:

(a) Thermo nuclear

(b) Uncontrolled fission

(c) Controlled fission

(d) Fusion

Ans. (b)