# Modern Physics

1. If K1 and K2 are the maximum kinetic energies of the photo electrons emitted by a light of wavelength λ1 and λ2 respectively. If λ1 = 2 λ2 , then
1) K1 = K2              2) K1 = K2/2                   3) K1 >  K2/2              4) K1< K2/2

2. The quantum number of Bohr orbit in Hydrogen atom whose radius is 0.01 nm is..
1) 235             2) 435            3) 123           4) 498

3. The electron in a Hydrogen atom makes transition from M shell to L Shell. The ratio of magnitudes of initial to final centripetal acceleration of the electron is..
1) 4 : 9           2)  9 : 4             3) 81 : 16                 4) 16 : 81

4. In a hypothetical system, a particle of mass m and charge -3q moving around a heavy particle having charge q. Assuming Bohr's model holds good to this system, the orbital velocity of mass m when it is nearest to the heavy particle is..

5. A Hydrogen atom is in an excited state of principal quantum number n. It emits a photon of wavelength λ while returning to the ground state. Then the value of n is..

6. Electrons with de - Broglie wavelength λ fall on the target in a X - ray tube. Then the cut off wavelength(λ0) of the emitted X - rays is..

7. The potential difference applied to an X - ray tube is 5kV and the current through it is 3.2 mA. Then the number of electrons striking the target per second is..
1) 1016               2) 2 × 1016            3) 1017           4) 2 × 1017

8. Two radioactive substances have decay constants 10λ0 and λ0. If initially they have the same number of nuclei, the ratio of number of their undecayed nuclei will be (1/e)  after a time..

9. A radioactive sample has 3.2 × 1016 active nuclei at certain instant. How many of these nuclei will still be in the same active state after four half - lives?
1) 1015              2) 2 × 1015              3) 1016             4) 2 × 1016

10. If elements of quantum number grater than n were not allowed, then the number of possible elements in the nature would be..
1) 1/2 n(n + 1)                     2) n2(n + 1)2/4
3) 1/3 n(n + 1)(2n + 1)       4) 1/6 n(n + 1)(2n + 1)

11. When a certain photosensitive surface is illuminated with monochromatic light of frequency υ, the stopping potential for photo electric current is V0/2. When the same surface is illuminated by monochromatic light of frequency υ/2, the stopping potential is V0. What is the threshold frequency for photoelectric emission?
1) υ/3           2) 3υ/2            3) 3υ                 4) 3υ/4

12. Photoelectrons with a maximum speed of 7 × 105 m/s are emitted from a metal surface when a light of frequency 8 × 1014 Hz falls on it. What is the threshold frequency of the surface?
1) 4.6 × 1014 Hz                  2) 3.6 × 1014 Hz                  3) 4.6 × 1015 Hz            4) 3.6 × 1015 Hz

13. Radiation of two photon energies twice and five times the work function of metal are incident successively on the metal surface. The ratio of the maximum velocity of the photoelectrons emitted in the two cases is..
1) 1 : 2          2) 2 : 1           3) 1 : 4           4) 4 : 1

14. What is the de−Broglie wavelength associated with an electron accelerated through a potential difference of 30 KV?
1) 1.24 °A            2) 2.24 °A              3) 1.84 °A                4) 3.84 °A

15. The speed of the electron in the first Bohr orbit of Hydrogen atom is (c = speed of light in Vacuum)
1) c               2) 137c                3) c/137            4) 13.7c

16. The angular momentum of an electron in the Hydrogen atom is 3h/2π (h represents Plank's constant). The kinetic energy of this electron is..
1) 2 eV               2) 4.5 eV               3) 3 eV              4) 1.51 eV

17. The first ionisation potential of hydrogen like Bohr atom is x. Then the value of the first excitation potential for this atom is
1) x            2) 3x/4           3) 4x/3            4) x/4

18. The wavelength of D1 and D2 lines of sodium are 5890 °A and 5896 °A respectively. If their mean wavelength is 6000 °A, find the difference of excited energy states.
1) 10-3 eV              2) 2 × 10-3 eV            3) 3 × 10-3 eV            4) 4 × 10-3 eV

19. If the wavelength of the first member of the Balmer series of Hydrogen spectrum is 6562 °A, then the wavelength of the first member of Lyman series in the same spectrum is (approx)..
1) 1215 °A             2) 6000 °A             3) 1315 °A            4) 6315 °A

20. The electric field associated with a light wave is E = E0 sin [1.57 × 107 (x - ct)], where x is in meter and t is in second. If this light is used to produce photoelectric emission, from the surface of a metal whose work function is 1.9 eV, then the stopping potential is
1) 1 Volt           2) 1.2 V             3) 2 V             4) 2.2 V

21. Two identical photo cathodes receive light of frequencies f1 and f2. If the velocities of the photo electrons (of mass m) coming out are v1 and v2 respectively, then

22. If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100W lamp? (Assume wave length of visible light as 5.6 × 10-5 cm)
1) 3 × 104              2) 3 × 103             3) 1.4 × 10-19            4) 1.4 × 1019

23. Let ν1 be the frequency of series limit of Lyman series, ν2 the frequency of the first line of Lyman series, and ν3 the frequency of series limit of Balmer series. Then which of the following is correct?
1) ν1 + ν2 = ν3            2) ν1 - ν2 = ν3           3) ν1 = ν23           4) ν= 1/2 (ν1 + ν2)

24. A stationary hydrogen atom of mass M emits a photon corresponding to the first line of Lyman series. If R is the Rydberg's constant, the velocity that the atom acquires is

25. If potential energy between a proton and an electron is given by |U| = ke2/2Rwhere 'e' is the charge of electron and R is the radius of atom, then radius of bohr's orbit is given by

26. The approximate value of quantum number n for the circular orbit of hydrogen of 0.0001 mm in diameter is..
1) 20                2) 31         3) 1000             4) 10

27. Magnetic field at the centre (at nucleus) of the hydrogen like atoms (atomic number = z) due to the motion of electron in nth orbit is proportional to

28. A sample of radioactive material decays simultaneously by two processes A and B with half-lives 1/2 and 1/4 hr respectively. For first half an hour it delays with the process A, next one hour with the process B, and for further half an hour with both A and B. If originally there were N0 nuclei, the number of nuclei after 2 hr of such decay is..

29. The activity of a radioactive element decreases to one-third of the original activity Ao in a period of 9 years. After a further lapse of 9 years, its activity will be..
1) Ao                 2) 9Ao                 3) 3Ao                       4) Ao/9

30. At any instant, the ratio of the amounts of two radio active substances is 2 : 1. If their half−lives be, respectively, 12h and 16h, then after two days what will be the ratio of the substances?
1) 1 : 1               2) 1 : 2               3) 2 : 1             4) 3 : 4

31. A radioactive sample undergoes decay as per the following graph. At time t = 0, the number of undecayed nuclei is No. Then the number of nuclei left after 1h is..

32. A proton of mass 'm' moving with a speed Vo approaches a stationary proton that is free to move. Assume impact parameter to be zero, i.e., head-on collision. How close will the incident proton go to other proton?

33. If 10,000 V are applied across an X-ray tube, the ratio of wavelength of the incident electrons and the shortest wavelength of X-ray coming out of the X-ray tube is (e/m of electron = 1.8 × 1011C kg-1)
1) 1 : 5              2) 5 : 1                3) 1 : 10                  4) 10 : 1

34. At a certain instant, a radioactive sample has a decay rate of 5000 disintigrations per minute. After 5 minutes, the decay rate is 1250 disintigrations per minute. Then the decay constant (per minute) is..
1) 0.4 ln (2)               2) 0.2 ln (2)                 3) 0.1 ln (2)          4) 0.8 ln (2)

ANSWERS: 1-4; 2-2; 3-4; 4-2; 5-3; 6-1; 7-2; 8-4; 9-2; 10-3; 11-2; 12-1; 13-1; 14-2; 15-3; 16-4; 17-2; 18-2; 19-1; 20-2; 21-2; 22-4; 23-2; 24-4; 25-2; 26-2; 27-1; 28-4; 29-4; 30-1; 31-4; 32-1; 33-3; 34-1.

Posted Date : 20-03-2021

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గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.