464 + Interview Questions in ATOMS IN GENERAL AWARENESS Page 4 InterviewSolution

151.	The `K_(alpha)andK_(beta)` lines of charateristic X-ray spectrum of molybdenum are `0.76 overset(@)A and 0.64overset(@)A`, respectively. The wavelength of `L_(alpha)` line isA. `1.4overset(@)A`B. `2.4overset(@)A`C. `4.1overset(@)A`D. `3.6overset(@)A`
Answer» Correct Answer - C `E_(2)E_(1)=(12375)/(0.76)eV` `E_(3)-E_(1)=(12375)/(0.76) eV` `:. " " E_(3)-E_(2)=(12375)/(0.64)-(12375)/(0.76)` or `" " lambda_(L_(alpha))=(12375)/(E_(3)-E_(2))=4.1Å`

Discussion

152.	Excitation energy of a hydrogen like ion in its first excitation state is 40.8 eV. Energy needed to remove the electron from the ion in gruond state isA. 54.4 eVB. 13.6 eVC. 40.8 eVD. 27.2 eV
Answer» Correct Answer - A Excitation energy , `DeltaE =E_(2)-E_(1)=13.6 [(1)/(1^(2))-(1)/(2^(2))]` `" " 40.8=13.6 Z^(2)xx(3)/(4)` `:. " " Z=2` So, required energy to remove the electron from gound state `=+(13.6Z^(2))/((1)^(2))=13.6(2)^(2)=54.4 eV`

Discussion

153.	In X-ray spectrum wavelength `lamda` of line `K_(alpha)` depends on atomic number Z asA. `lambda propZ^(2)`B. `lambdaprop(Z-1)^(2)`C. `lambdaprop(1)/((Z-1))`D. `lambdaprop(1)/((Z-1)^(2))`
Answer» Correct Answer - D In X-ray spectrum wavelength `lambda` of `K_(alpha)` line is given by `(1)/(lambda_(K_(alpha)))=(3)/(4)(Z-1)^(2)` `:. " " lambda_(K_(alpha))prop(1)/((Z-1)^(2))`

Discussion

154.	Molybdenum is used as a target element for production of `X` - rays because it isA. light and can easily deflect electronsB. light can absorb electronsC. a heavy element with a high melting pointD. an element having high thermal conductivity
Answer» Correct Answer - D

Discussion

155.	The nuclear radius of `Pb^(208)` is is 8.874 fm. What will be the nuclear radius of `Ca^(44)` ?
Answer» Correct Answer - 5.286 fm

Discussion

156.	Find the mass energy of a particle of mass 1 g in joule.
Answer» Data : m = 1 g = 1 × 10^-3 kg, c = 3 × 10⁸ m/s, 1 eV = 1.602 × 10^-19 J The mass energy, E = mc² = (1 × 10^-3)(3 × 10⁸)² = 9 × 10¹³ J

156.

Find the mass energy of a particle of mass 1 g in joule.

Answer»

Data : m = 1 g = 1 × 10^-3 kg,

c = 3 × 10⁸ m/s,

1 eV = 1.602 × 10^-19 J

The mass energy,

E = mc²

= (1 × 10^-3)(3 × 10⁸)²

= 9 × 10¹³ J

Discussion

157.	When a β-particle is emitted by a nucleus, its mass number (A) decreases (B) remains the same (C) increases (D) may decrease or increase.
Answer» (B) remains the same

Discussion

158.	When an α-particle is emitted by a nucleus, its mass number (A) increases by 4 (B) decreases by 4 (C) increases by 2 (D) decreases by 2.
Answer» (B) decreases by 4

Discussion

159.	Among alpha, beta and gamma radiations, which get affected by the electric field ?
Answer» Alpha and Beta radiations are get affected by the electric field.

Discussion

160.	The Lyman series of hydrogen spectrum lies in the ultraviolet region. Why?
Answer» The calculated values of wavelengths lie in the ultraviolet region of the spectrum-well agree with the values of wavelengths observed experimentally by Lyman.

Discussion

161.	Spectrum of X-rays isA. continuousB. linearC. continuous and linearD. band
Answer» Correct Answer - A Continuous spectrum or X-rays consist of radiatiosof all possible X-rays wavelength within a certain range starting from `lambda_("min")` onwards.

Discussion

162.	The spectral series of the hydrogen spectrum that lies in the ultraviolet region is theA. Balmer seriesB. Brackett seriesC. Paschen seriesD. Lyman series
Answer» Correct Answer - D

Discussion

163.	Who proposed the first model of an atom?
Answer» J.J. Thomson proposed the first model of an atom in the year 1898.

Discussion

164.	What is the electric charge on an atom?
Answer» At atom of an element is electrically neutral.

Discussion

165.	Who discovered electrons?
Answer» Electrons were discovered by J.J Thomason in the year 1897.

Discussion

166.	What are the Limitations of Bohr atom ?
Answer» Bohr model can also be used for the studies of spectra of hydrogen like elements . Inspite of its tremendous success the Bohr model could not explain the observed fine structure of spectral lines in the hydrogen spectrum.

Discussion

167.	Explain the Limitations of Bohr model.
Answer» Bohr model involves classical trajectory picture (planet-like electron orbiting the nucleus), correctly predicts the gross features of the hydrogenic atoms*, in particular, the frequencies of the radiation emitted or selectively absorbed. This model however has many limitations. Some are: (i) The Bohr model is applicable to hydrogenic atoms. It cannot be extended even to mere two electron atoms such as helium. The analysis of atoms with more than one electron was attempted on the lines of Bohr’s model for hydrogenic atoms but did not meet with any success. Difficulty lies in the fact that each electron interacts not only with the positively charged nucleus but also with all other electrons. The formulation of Bohr model involves electrical force between positively charged nucleus and electron. It does not include the electrical forces between electrons which necessarily appear in multi-electron atoms. (ii) While the Bohr’s model correctly predicts the frequencies of the light emitted by hydrogenic atoms, the model is unable to explain the relative intensities of the frequencies in the spectrum. In emission spectrum of hydrogen, some of the visible frequencies have weak intensity, others strong. Why? Experimental observations depict that some transitions are more favoured than others. Bohr’s model is unable to account for the intensity variations. Bohr’s model presents an elegant picture of an atom and cannot be generalised to complex atoms. For complex atoms we have to use a new and radical theory based on Quantum Mechanics, which provides a more complete picture of the atomic structure.

167.

Explain the Limitations of Bohr model.

Answer»

Bohr model involves classical trajectory picture (planet-like electron orbiting the nucleus), correctly predicts the gross features of the hydrogenic atoms*, in particular, the frequencies of the radiation emitted or selectively absorbed. This model however has many limitations. Some are:

(i) The Bohr model is applicable to hydrogenic atoms. It cannot be extended even to mere two electron atoms such as helium. The analysis of atoms with more than one electron was attempted on the lines of Bohr’s model for hydrogenic atoms but did not meet with any success. Difficulty lies in the fact that each electron interacts not only with the positively charged nucleus but also with all other electrons. The formulation of Bohr model involves electrical force between positively charged nucleus and electron. It does not include the electrical forces between electrons which necessarily appear in multi-electron atoms.

(ii) While the Bohr’s model correctly predicts the frequencies of the light emitted by hydrogenic atoms, the model is unable to explain the relative intensities of the frequencies in the spectrum. In emission spectrum of hydrogen, some of the visible frequencies have weak intensity, others strong. Why? Experimental observations depict that some transitions are more favoured than others. Bohr’s model is unable to account for the intensity variations.

Bohr’s model presents an elegant picture of an atom and cannot be generalised to complex atoms. For complex atoms we have to use a new and radical theory based on Quantum Mechanics, which provides a more complete picture of the atomic structure.

Discussion

168.	Assertion By increasing the accelerationg voltage in coolidge tube wavelength of characteristic X-rays does not change. Reason Cut-off wavelength is inversely proportional to the acceleration voltageA. If both Assertion and Reason ar true and Reason is the correct explanation of Assertion.B. If both Assertion and Reason are true but Reason is not correct explanation of AssertionC. If Assertion is true by Reason is false.D. If Assertion is false but Reason is true.
Answer» Correct Answer - B

Discussion

169.	An electron in a hydrogen atom makes a transition such that its kinetic energy increases, thenA. The electron may have excited form n=2 to n=3B. Potential energy of the electron increasesC. Potential energy of the electron decreasesD. Total energy of the electron increases
Answer» Correct Answer - C

Discussion

170.	If the wavelength of the firsr line of the Blamer series of hydrogen atom is `6561Å` , the wavelength of the second line of the series should beA. 13122ÅB. 3280ÅC. 4860ÅD. 2187Å
Answer» Correct Answer - C Wavlength of spectral line in Blamer series is given by `" " (1)/(lambda)=R[(1)/(2^(2))-(1)/(n^(2))]` For first line of Blamer series,n=3 `:." " (1)/(lambda)=R[(1)/(2^(2))-(1)/(3^(2))]=(5R)/(36)` For second line of Balmer series n=4 `" " (1)/(lambda)=R((1)/(2^(2))-(1)/(4^(2)))=(3R)/(16)` `:. " " (lambda_(2))/(lambda_(1))=(20)/(27)` `:." " lambda_(1)=(20)/(27)xx6561=4860Å`

Discussion

171.	The ratio of the wavelengths for `2 rarr 1` transition in `Li^(++), He^(+)` and `H` isA. `1:2:3`B. `1:4:9`C. `2:9:36`D. `3:2:1`
Answer» Correct Answer - C `(1)/(lambda)=RZ^(2)((1)/(n_(1)^(2))-(1)/(n_(2)^(2)))rArrlambdaprop(1)/(Z^(2))` `lambda_(Li^(++)):lambda_("He"^(+)):lambda_(H)=4:9:36`

Discussion

172.	The radius of hydrogen atom in its ground state is `5.3 xx 10^-11 m`. After collision with an electron it is found to have a radius of `21.2 xx 10^-11 m`. The principal quantum number of the final state of the atom is.A. n=4B. n=2C. n=16D. n=3
Answer» Correct Answer - B `rpropn^(2)i.e.,(""^rf)/(r_(i))=((n_(f))/(n_(i)))^(2)` `rArr " " (21.2xx2xx10^(-11))/(5.3xx10^(-11))=((n)/(1))^(2)rArrn^(2)=4rArrn=2`

Discussion

173.	In hydrogen atom, electron makes transition from `n = 4` to `n = 1` level. Recoil momentum of the `H` atom will beA. `13.6xx10^(-19) kg ms^(-1)`B. `6.8xx10^(-27) kg ms^(-1)`C. `12.75xx10^(-24) kg ms^(-1)`D. None of these
Answer» Correct Answer - B `DeltaE_((4-1))=(13.6-(13.6)/(16))eV=12.75 eV` Momentum of hydrogen atom = Momentum of photon `" " =(E)/(c)=(12.75xx1.6xx10^(-19))/(3.0xx10^(8))=6.8xx100^(-27) kg ms^(-1)`

Discussion

174.	Speed `(V_(n))` of electron in nth orbit versus principal quantum number (n) graphs isA. B. C. D.
Answer» Correct Answer - B

Discussion

175.	An electron with kinetic energy `5eV` is incident on a hydrogen atom in its ground state.The collisionA. must be elasticB. may be partially elasticiC. must be completely inelasticD. may be completely inelastic
Answer» Correct Answer - A In hydrogen atom `E_(2)-E_(1)=10.2 eV` Since,` " " 5 eV lt 10.2 eV` The electron cannot excite the hydrogen atom. The collision must be therefore elastic .

Discussion

176.	Hard `X` -rays for the study of fractures in bones should have a minimum wavelength of `10^(-11) m`. The accelerating voltage for electrons in `X` -ray machine should beA. `lt 124.2 kV`B. `gt 124.2 kV`C. Between 60 kV and 70 kVD. equal to 100 kVs
Answer» Correct Answer - A `V_("max")=(12400xx10^(-10))/(10^(-11))=124 kVrArrVlt124 kV`

Discussion

177.	STATEMENT-1:Intensity of X-rays is dependent upon filament current. STATEMENT-2:Penetrating power depends upon accelerating voltage. STATEMENT-3:The value of X-ray photon is generally in keVA. TTFB. TFTC. FTFD. TTT
Answer» Correct Answer - D

Discussion

178.	STATEMENT-1:Continuous X-rays depends only on the accelerating voltage V. STATEMENT-2:Characteristic X-ray depends on filament and cathode. STATEMENT-3:In coolidge tube kinetic energy of a moving electron is converted into a X-ray photon.A. TTFB. TFTC. TTTD. FTF
Answer» Correct Answer - B

Discussion

179.	The relationship between kinetic energy (K) and potential energy (U) of electron moving in a orbit arund the nucleus isA. `U=-K`B. `U=-2K`C. `U=-3K`D. `U=-(1)/(2)K`
Answer» Correct Answer - B Kinetic energy, `K=(1)/(2)mv^2=(e^2)/(8piepsilon_0r)` and P.E.,`U=-(e^2)/(4piepsilon_0r)` or `K=(1)/(2)mv^2=(e^2)/(8piepsilon_0r)rArrU=-2K`.

Discussion

180.	With increase in n, ionisation energy will increase or decrease ?
Answer» Correct Answer - Decrease

Discussion

181.	Which element has a ` K_(alpha)` line of wavlength 1.785Å ?A. CopperB. cobaltC. SodiumD. Aluminium
Answer» Correct Answer - B We know that, `(1)/(lambda_(k_alpha))=R(Z-1)^(2)((1)/(1^(2))-(1)/(2^(2)))` `" " (Z-1)^(2)=(4)/(3)xx(1)/(lambda_(k_(alpha))R)=680` `" " (Z-1)=26` `" " Z=27to` cobalt

Discussion

182.	A H-atom moving with speed v makes a head on collision with a H-atom in rest. Both atoms are in ground state. Find the minimum value of velocity v for which one of atom may excite.A. `6.25xx10^(4)ms^(-1)`B. `8xx10^(4)ms^(-1)`C. `7.25xx10^(4)ms^(-1)`D. `13.6xx10^(4)ms^(-1)`
Answer» Correct Answer - A Minimum 10.2 eV energy is required to exctie a hydrogen atom. In perfectly inelastic collison maximum energy is lost. `:. "energy los" =(1)/(2)(2m)((v)/(2))^(2)=10.2xx1.6xx10^(-19)` `" " (1)/(4)mv^(2)=1.632xx10^(-18)` `:. "velocity"vsqrt((1.632xx4xx10^(-18))/(1.67xx10^(-27)))=6.25xx10^(4)ms^(-1)`

Discussion

183.	In an inelastic collision an electron excites a hydrogen atom from its ground state to a M-Shell state. A second electron collides instantaneously with the excited hydrogen atom in the m-Shell state and ionizes it. At leas how much energy the second electron transfors to the atom is the M-shell state?A. `+3.4 eV`B. `+1.51 eV`C. ` -3.4 eV`D. `-1.51 eV`
Answer» Correct Answer - D The ground state of hydrogen (n=1) is represented by K, the first excited state (n=2) is represented by L,the second excited state (n=3) is represent byb M.So, the energy transferred by the second electron cab be given by `E=-13.6((1)/(n_(1)^(2))-(1)/(n_(2)^(2)))=-13.6 ((1)/(3^(2))-(1)/(oo^(2)))=-1.51ev`

Discussion

184.	If radius of first orbit of hydrogen atom is `5.29xx10^(-11)` m, the radius of fourth orbit will beA. 8.46 ÅB. 10.23 ÅC. 9.22 ÅD. 9.48 Å
Answer» Correct Answer - A

Discussion

185.	What is the equivalent energy of a 10 mg mass ?
Answer» Correct Answer - `9 xx 10^(9) J`

Discussion

186.	When `._(92)U^(235)` undergoes fission, 0.1% of the original mass is released into energy. How much energy is released by an atom bomb which contains `10kg` of `._(92)U^(235)`?
Answer» Correct Answer - `9 xx 10^(14)` J

Discussion

187.	The half life of `._(90)Th^(225)` is 8 minutes How many half lives are there in 2 hours ? How long would you have to wait before there is less than 1 % of `._(90)Th^(225)` left in the sample ?
Answer» Correct Answer - `15; 53.15` min

Discussion

188.	For a given sample, the count rate is `47.5alpha` particle per minute. After 5 minutes, the count is reduced to `27 alpha` particles per minute. Find the decay constant and half life of the sample.
Answer» Correct Answer - `0.0019 s^(-1) 368.12 s`

Discussion

189.	Name the physicists who for the first time verified the wave nature of electrons.
Answer» C.J. Davisson and L.H. Germer verified the wave nature of electrons.

Discussion

190.	How does Rydberg’s constant vary with atomic number?
Answer» R = Z² R_H, where Z = atomic number. R is directly proportional to Z² R_H = Rydberg’s constant for hydrogen atom.

Discussion

191.	What is the value of ionization potential of 42He atom ?
Answer» I.E = -(13.6 eV)Z² put Z = 2 I.E = -13.6(2)² eV = -54.4 eV. Ionisation potential = -54.4 V.

191.

What is the value of ionization potential of 42He atom ?

Answer»

I.E = -(13.6 eV)Z² put Z = 2 I.E = -13.6(2)² eV = -54.4 eV.

Ionisation potential = -54.4 V.

Discussion

192.	Consider a hydrogen-like atom whose energy in nth excited state is given by `E_(n) = (13.6 Z^(2))/(n^(2))` When this excited makes a transition from excited state to ground state , most energetic photons have energy `E_(max) = 52.224 eV`. and least energetic photons have energy `E_(max) = 1.224 eV` Find the atomic number of atom and the intial state or excitation.A. 2B. 4C. 5D. None of these
Answer» Correct Answer - A Maximum energy is liberated for transition `E_(n)rarr1` and minimum energy for `E_(n)rarrE_(n-1)` Hence `(E_(1))/(n^(2))-E_(1)=52.224eV " " ....(i)` and `(E_(1))/(n^(2))-(E_(1))/((n-1))=1.224eV" " ....(ii)` Solving Eqs. (i) and (ii), we get `E_(1)=-54.4eV and n=5` But `E_(1)=-(13.6Z^(2))/(1^(2))` `:. -54.4=(13.)/(1^(2))Z^(2)rArrZ=2`

Discussion

193.	In a radioactive transformation, a change in the mass number occurs with (A) α- or β-decay (B) β-decay (C) γ-decay (D) α-decay.
Answer» Correct option is (D) α-decay.

Discussion

194.	A does of 5 mc of 3015P is administered intravenously to a patient whose blood volume is 3.5 litre. At the end of one hour it is assumed that the phosphorus is uniformly distributed. Then the count rate after per ml of withdrawn blood after one hour is (assume that the counter had an efficiency of only 10%). Given 1 mc = 3.7×107 dis/s and half life of phosphorous is 14 day.(1) 5.3×102 dis/s (2) 5.0×103 dis/s (3) 5.3×107 dis/s(4) 530 dis/s
Answer» Correct option : (1) 5.3×10² dis/s Explanation: Dose per ml = 5/3500 mc Number of disintegration 1/700 x 3.7 x 10⁷ per sec. in blood After one hour we can assume no decay. Disintegration counted = 1/10 x 1/700 x 3.7 x 10⁷ = 5.3×10² dis/s

194.

A does of 5 mc of 3015P is administered intravenously to a patient whose blood volume is 3.5 litre. At the end of one hour it is assumed that the phosphorus is uniformly distributed. Then the count rate after per ml of withdrawn blood after one hour is (assume that the counter had an efficiency of only 10%). Given 1 mc = 3.7×107 dis/s and half life of phosphorous is 14 day.(1) 5.3×102 dis/s (2) 5.0×103 dis/s (3) 5.3×107 dis/s(4) 530 dis/s

Answer»

Correct option : (1) 5.3×10² dis/s

Explanation:

Dose per ml = 5/3500 mc

Number of disintegration 1/700 x 3.7 x 10⁷ per sec. in blood

After one hour we can assume no decay.

Disintegration counted = 1/10 x 1/700 x 3.7 x 10⁷

= 5.3×10² dis/s

Discussion

195.	Explain drawbacks of Rutherford Model.
Answer» (a) According to Rutherford, an atom consisting of a central nucleus and revolving electron is stable much like sun-planet system with electro-static force of attraction and object (electron) which moves in a circle is being constantly accelerated – the acceleration being centripetal in nature. According to classical electromagnetic theory, an accelerating charged particle emits radiation in the form of electromagnetic waves. The energy of an accelerating electron should therefore, continuously decrease. The electron would spiral inward and eventually fall into the nucleus. Thus, such an atom can not be stable. But most of the atoms in nature are stable which is against Rutherford model. (b) According to the classical electromagnetic theory, the frequency of the electromagnetic waves emitted by the revolving electrons is equal to the frequency of revolution. As the electrons spiral inwards, their angular velocities and hence their frequencies would change continuously, and so will the frequency of the light emitted. Thus, they would emit a continuous spectrum, in contradiction to the line spectrum actually observed. Rutherford model which depends on the classical ideas are not sufficient to explain the atomic structure.

195.

Explain drawbacks of Rutherford Model.

Answer»

(a) According to Rutherford, an atom consisting of a central nucleus and revolving electron is stable much like sun-planet system with electro-static force of attraction and object (electron) which moves in a circle is being constantly accelerated – the acceleration being centripetal in nature.

According to classical electromagnetic theory, an accelerating charged particle emits radiation in the form of electromagnetic waves. The energy of an accelerating electron should therefore, continuously decrease. The electron would spiral inward and eventually fall into the nucleus. Thus, such an atom can not be stable. But most of the atoms in nature are stable which is against Rutherford model.

(b) According to the classical electromagnetic theory, the frequency of the electromagnetic waves emitted by the revolving electrons is equal to the frequency of revolution. As the electrons spiral inwards, their angular velocities and hence their frequencies would change continuously, and so will the frequency of the light emitted. Thus, they would emit a continuous spectrum, in contradiction to the line spectrum actually observed.

Rutherford model which depends on the classical ideas are not sufficient to explain the atomic structure.

Discussion

196.	Assertion Second orbit circumference of hydrogen atom is two times the de-Broglie wavelength of electrons in that orbit Reason de-Broglie wavelength of electron in ground state is minimum.A. If both Assertion and Reason ar true and Reason is the correct explanation of Assertion.B. If both Assertion and Reason are true but Reason is not correct explanation of AssertionC. If Assertion is true by Reason is false.D. If Assertion is false but Reason is true.
Answer» Correct Answer - B `mv_(2)r_(2)=2((h)/(2pi))` `:.2pir_(2)=2((h)/(mv_(2)))=2lambda_(2)` Further `lambda=(h)/(p)` Speed of momentum is maximum is ground state. Hence `lambda` is minimum

Discussion

197.	The magnetic fieold at the centre of a hydrogen atom due to the motion of the electron in the first Bohr orbit is B . The magnetic field at the centre due to the motion of the electron in the second Bohr orbit will be `(B)/(2^(x))`Find value of x.A. `B/4`B. `B/8`C. `B/32`D. `B/64`
Answer» Correct Answer - C

Discussion

198.	Pick out the correct statement from the followingA. Mercury vapour lam produces lines emission spectrumB. Oil flame produces line emission spectrumC. Band spectrum helps us to study molecular structureD. Sunlight spectrum is an example for line absroption spectrum
Answer» Correct Answer - A::C::D The line emission spectra is produced by excited substance in atomic state, as by mercury vapour lamp. Line absorption spectra state, is produced by e.m. ratiations, that has passed through a medium hence, sunlight spectrum is a line absorption spectrum. The Band spectrum is used to study the molecular structrue. Here,a,c, and d are the correct statements.

Discussion

199.	Ligth emitted during the de excitation of electrons from n=3 to n=2, when incident on metal, photoelectrons following de excitations photoelectrons are just emitted from that metal. In which of the following de excitations photoelectric effect, is not possible ?A. From n=2 to n=1B. From n=3 to n=1C. From n=5 to n=2D. From n= to n=1
Answer» Correct Answer - D The photoelectric effect is possible when light of sufficient energy incident on metal surface. When electron de excites from n=3 to n=2 ,the produces photoeletrif effect. So for the given options, the photoelectric effect is not possible for that level in which energy of emitted light is less than that for n=3 to n=2 `(hv)_(4-3) lt (hv)_(3-2)` Hence, photoelectric effect is not possible.

Discussion

200.	When ultraviolet radiation is incident on a surface, no photoelectrons are emitted. If another beam causes photoelectrons to be emitted from the surface, it may consist of (i) radio waves (ii) infrared rays (iii) X-rays (iv) gamma raysA. infra-red lightB. Visible lightC. X-raysD. Micro-waves
Answer» Correct Answer - C

Discussion

Explore topic-wise InterviewSolutions in .

The `K_(alpha)andK_(beta)` lines of charateristic X-ray spectrum of molybdenum are `0.76 overset(@)A and 0.64overset(@)A`, respectively. The wavelength of `L_(alpha)` line isA. `1.4overset(@)A`B. `2.4overset(@)A`C. `4.1overset(@)A`D. `3.6overset(@)A`

Excitation energy of a hydrogen like ion in its first excitation state is 40.8 eV. Energy needed to remove the electron from the ion in gruond state isA. 54.4 eVB. 13.6 eVC. 40.8 eVD. 27.2 eV

In X-ray spectrum wavelength `lamda` of line `K_(alpha)` depends on atomic number Z asA. `lambda propZ^(2)`B. `lambdaprop(Z-1)^(2)`C. `lambdaprop(1)/((Z-1))`D. `lambdaprop(1)/((Z-1)^(2))`

Molybdenum is used as a target element for production of `X` - rays because it isA. light and can easily deflect electronsB. light can absorb electronsC. a heavy element with a high melting pointD. an element having high thermal conductivity

The nuclear radius of `Pb^(208)` is is 8.874 fm. What will be the nuclear radius of `Ca^(44)` ?

Find the mass energy of a particle of mass 1 g in joule.

When a β-particle is emitted by a nucleus, its mass number (A) decreases (B) remains the same (C) increases (D) may decrease or increase.

When an α-particle is emitted by a nucleus, its mass number (A) increases by 4 (B) decreases by 4 (C) increases by 2 (D) decreases by 2.

Among alpha, beta and gamma radiations, which get affected by the electric field ?

The Lyman series of hydrogen spectrum lies in the ultraviolet region. Why?

Spectrum of X-rays isA. continuousB. linearC. continuous and linearD. band

The spectral series of the hydrogen spectrum that lies in the ultraviolet region is theA. Balmer seriesB. Brackett seriesC. Paschen seriesD. Lyman series

Who proposed the first model of an atom?

What is the electric charge on an atom?

Who discovered electrons?

What are the Limitations of Bohr atom ?

Explain the Limitations of Bohr model.

An electron in a hydrogen atom makes a transition such that its kinetic energy increases, thenA. The electron may have excited form n=2 to n=3B. Potential energy of the electron increasesC. Potential energy of the electron decreasesD. Total energy of the electron increases

If the wavelength of the firsr line of the Blamer series of hydrogen atom is `6561Å` , the wavelength of the second line of the series should beA. 13122ÅB. 3280ÅC. 4860ÅD. 2187Å

The ratio of the wavelengths for `2 rarr 1` transition in `Li^(++), He^(+)` and `H` isA. `1:2:3`B. `1:4:9`C. `2:9:36`D. `3:2:1`

The radius of hydrogen atom in its ground state is `5.3 xx 10^-11 m`. After collision with an electron it is found to have a radius of `21.2 xx 10^-11 m`. The principal quantum number of the final state of the atom is.A. n=4B. n=2C. n=16D. n=3

In hydrogen atom, electron makes transition from `n = 4` to `n = 1` level. Recoil momentum of the `H` atom will beA. `13.6xx10^(-19) kg ms^(-1)`B. `6.8xx10^(-27) kg ms^(-1)`C. `12.75xx10^(-24) kg ms^(-1)`D. None of these

Speed `(V_(n))` of electron in nth orbit versus principal quantum number (n) graphs isA. B. C. D.

An electron with kinetic energy `5eV` is incident on a hydrogen atom in its ground state.The collisionA. must be elasticB. may be partially elasticiC. must be completely inelasticD. may be completely inelastic

Hard `X` -rays for the study of fractures in bones should have a minimum wavelength of `10^(-11) m`. The accelerating voltage for electrons in `X` -ray machine should beA. `lt 124.2 kV`B. `gt 124.2 kV`C. Between 60 kV and 70 kVD. equal to 100 kVs

STATEMENT-1:Intensity of X-rays is dependent upon filament current. STATEMENT-2:Penetrating power depends upon accelerating voltage. STATEMENT-3:The value of X-ray photon is generally in keVA. TTFB. TFTC. FTFD. TTT

STATEMENT-1:Continuous X-rays depends only on the accelerating voltage V. STATEMENT-2:Characteristic X-ray depends on filament and cathode. STATEMENT-3:In coolidge tube kinetic energy of a moving electron is converted into a X-ray photon.A. TTFB. TFTC. TTTD. FTF

The relationship between kinetic energy (K) and potential energy (U) of electron moving in a orbit arund the nucleus isA. `U=-K`B. `U=-2K`C. `U=-3K`D. `U=-(1)/(2)K`

With increase in n, ionisation energy will increase or decrease ?

Which element has a ` K_(alpha)` line of wavlength 1.785Å ?A. CopperB. cobaltC. SodiumD. Aluminium

A H-atom moving with speed v makes a head on collision with a H-atom in rest. Both atoms are in ground state. Find the minimum value of velocity v for which one of atom may excite.A. `6.25xx10^(4)ms^(-1)`B. `8xx10^(4)ms^(-1)`C. `7.25xx10^(4)ms^(-1)`D. `13.6xx10^(4)ms^(-1)`

If radius of first orbit of hydrogen atom is `5.29xx10^(-11)` m, the radius of fourth orbit will beA. 8.46 ÅB. 10.23 ÅC. 9.22 ÅD. 9.48 Å

What is the equivalent energy of a 10 mg mass ?

When `._(92)U^(235)` undergoes fission, 0.1% of the original mass is released into energy. How much energy is released by an atom bomb which contains `10kg` of `._(92)U^(235)`?

The half life of `._(90)Th^(225)` is 8 minutes How many half lives are there in 2 hours ? How long would you have to wait before there is less than 1 % of `._(90)Th^(225)` left in the sample ?

For a given sample, the count rate is `47.5alpha` particle per minute. After 5 minutes, the count is reduced to `27 alpha` particles per minute. Find the decay constant and half life of the sample.

Name the physicists who for the first time verified the wave nature of electrons.

How does Rydberg’s constant vary with atomic number?

What is the value of ionization potential of 42He atom ?

In a radioactive transformation, a change in the mass number occurs with (A) α- or β-decay (B) β-decay (C) γ-decay (D) α-decay.

Explain drawbacks of Rutherford Model.

The magnetic fieold at the centre of a hydrogen atom due to the motion of the electron in the first Bohr orbit is B . The magnetic field at the centre due to the motion of the electron in the second Bohr orbit will be `(B)/(2^(x))`Find value of x.A. `B/4`B. `B/8`C. `B/32`D. `B/64`

Pick out the correct statement from the followingA. Mercury vapour lam produces lines emission spectrumB. Oil flame produces line emission spectrumC. Band spectrum helps us to study molecular structureD. Sunlight spectrum is an example for line absroption spectrum

When ultraviolet radiation is incident on a surface, no photoelectrons are emitted. If another beam causes photoelectrons to be emitted from the surface, it may consist of (i) radio waves (ii) infrared rays (iii) X-rays (iv) gamma raysA. infra-red lightB. Visible lightC. X-raysD. Micro-waves