Assertion (A): Bohr postulates that the electrons in stationary orbits around the nucleus do not radiate.
Reason (R): According to classical physics all moving electrons radiate.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Bohr's first postulate (A) states that electrons in stationary orbits do not radiate energy. This postulate was introduced to address the classical physics problem (R) where accelerating charged particles, like orbiting electrons, should continuously radiate energy.
Thus, both (A) and (R) are true, and (R) provides the underlying classical paradox that Bohr's postulate (A) resolved.
Assertion (A): Anode of Coolidge tube gets heated up at time of emission of X-rays.
Reason (R): The anode of Coolidge tube is made of a material of high melting point.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
When high-energy electrons strike the anode in an X-ray tube, most of their kinetic energy (around 99%) is converted into heat, causing the anode to get very hot. So (A) is true. Because of this extreme heating, the anode is made from materials with a high melting point, like Tungsten, to withstand the temperature. So (R) is true. However, (R) describes a design choice made due to the heating, not the explanation for why heating occurs. Hence, (R) is not the correct explanation for (A).
Assertion (A): In a Bohr’s atom, frequency of revolution of an electron in its orbit is same as frequency of spectral line, for transition between large quantum numbers.
Reason (R): As Principal quantum number increases in a Bohr’s atom, energy gap between the energy levels decreases.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true due to the correspondence principle where for large \(n\), \(f_{\text{rev}} \propto 1/n^3\) and \(f_{\text{spectral}} \propto 1/n^3\).
Reason (R) is true because \(E_n \propto -1/n^2\), so \(Delta E = |E_{n+1} - E_n| \propto 1/n^3\). Reason (R) correctly explains why the spectral lines become closer, aligning with the classical revolution frequency for large \(n\).
Assertion (A): Wavelength of Lyman series is less than of Balmer series.
Reason (R): In hydrogen spectrum Balmer series belongs to visible spectrum.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true: Lyman series transitions end at \(n=1\) (higher energy, shorter \(lambda\)) while Balmer end at \(n=2\) (lower energy, longer \(\lambda\)).
Reason (R) is true: Balmer lines like \(H_\alpha\) and \(H_\beta\) are in the visible spectrum. However, (R) does not explain why Lyman has shorter wavelengths than Balmer, so it's not the correct explanation.
Assertion (A): The frequency of \(K_\alpha\) X-radiations is greater than \(K_\beta\) for a given target.
Reason (R): \(K_\alpha\) radiation is produced when an electron from \(n = 2\) jumps into the vacancy in \(n = 1\) orbit, whereas in \(K_\beta\) radiation the transition takes place from \(n = 3\) to \(n = 2\).
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is false: \(K_\beta\) (\(n=3 \to n=1\)) involves a larger energy difference than \(K_\alpha\) (\(n=2 \to n=1\)), so \(f_{K_\beta}\ > f_{K_\alpha}\). Reason (R) is false: While \(K_\alpha\) is \(n=2 \to n=1\), \(K_\beta\) is \(n=3 \to n=1\), not \(n=3 \to n=2\). Both are false.
Assertion (A): Frequency of characteristic X-ray will change if atomic number of target is changed.
Reason (R): When high energy electron strikes on target then characteristics and continuous X-rays are emitted.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true: Characteristic X-ray frequency depends on the atomic number \(Z\) of the target (Moseley's Law, \(f \propto (Z-b)^2\)). Reason (R) is true: Both characteristic and continuous X-rays are emitted during electron bombardment. However, (R) describes the emission process generally, not the \(Z\)-dependence of characteristic X-ray frequency, so it's not the correct explanation.
Assertion (A): A hydrogen atom can absorb a photon whose energy is greater than \(13.6\text{ eV}\).
Reason (R): The binding energy of a hydrogen atom is \(13.6\text{ eV}\).
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Binding energy of hydrogen atom is \(13.6\text{ eV}\). A photon with energy \(ge 13.6\text{ eV}\) can ionize the atom. Excess energy becomes \(K.E.\) of electron. So (A) is true. (R) states the binding energy. (R) correctly explains (A).
Assertion (A): A welder uses mouth mask for protection of eyes.
Reason (R): Welding arc produces X-rays.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Welders use face masks for eye protection from intense UV/Visible/IR radiation and sparks. So (A) is true. Welding arcs primarily emit strong UV radiation, not X-rays, as the main hazard. So (R) is false.
Assertion (A): The electron will be ejected from a hydrogen atom when electron beam of kinetic energy \(10.6\text{ eV}\) falls on it.
Reason (R): The difference between \(n_1\) and \(n_2\) is \(10.2\text{ eV}\).
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Ionization energy of H atom is \(13.6\text{ eV}\). \(10.6\text{ eV}\). is insufficient to ionize. \(\Delta E_{2-1} = 10.2\text{ eV}\). If 'ejected' means excited to \(n=2\), then (A) is true. (R) is true and explains the excitation.
Assertion (A): It is easier to release an orbital electron, but quite difficult to release a nucleon.
Reason (R): An electron is much lighter than a nucleon.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Electron binding energies are in eV, nucleon binding energies in MeV, so (A) is true. Electron mass \(9.11 \times 10^{-31}\text{ kg}\) is much less than nucleon mass \(1.67 \times 10^{-27}\text{ kg}\), so (R) is true. The difference in ease of release is due to different fundamental forces, not primarily mass. So (R) does not explain (A).