Chapter 13

Gases are bad conductors of electricity. Their conductivity may be increased by (a) increasing the pressure as well as potential difference between the electrodes. (b) decreasing the pressure as well as potential difference between the electrodes. (c) decreasing the pressure and/or increasing the potential difference between the electrodes. (d) increasing the pressure and/or decreasing the potential difference between the electrodes.

Specific charges of two particles \(\mathrm{A}\) and \(\mathrm{B}\) are in the ratio \(2: 3 .\) If the mass ratio, \(m_{\mathrm{A}}: m_{\mathrm{B}}\) is \(2: 3\), then the ratio of their charges, \(e_{\mathrm{A}}: e_{\mathrm{B}}\), is (a) \(1: 1\) (b) \(4: 9\) (c) \(9: 4\) (d) \(2: 3\)

An electron at rest is accelerated through a potential difference of \(200 \mathrm{~V}\). If the specific charge of electron is \(1.76 \times 10^{11} \mathrm{C} / \mathrm{kg}\), the speed acquired by the electron is about (a) \(8.4 \times 10^{6} \mathrm{~cm} / \mathrm{s}\) (b) \(8.4 \times 10^{6} \mathrm{~m} / \mathrm{s}\) (c) \(4.2 \times 10^{6} \mathrm{~m} / \mathrm{s}\) (d) \(4.2 \times 10^{6} \mathrm{~cm} / \mathrm{s}\)

The specific charge of cathode rays (a) depends on the nature of the gas. (b) depends on the material of the discharge tube. (c) depends on the potential difference between cathode and anode. (d) is a universal constant.

Which of the following is not a fundamental particle? (a) Electron (b) Proton (c) Neutron (d) X-rays

An electron and a proton are accelerated through a potential \(V\). If \(P_{\mathrm{c}}\) and \(P_{\mathrm{p}}\) are their momentum, then \(P_{\mathrm{p}}: P_{\mathrm{e}}\) ratio is approximately equal to (a) \(1: 1836\) (b) \(1: 1\) (c) \(1836: 1\) (d) \(43: 1\)

The presence of charge particles in the atoms was first confirmed by (a) Rutherford (b) Thomson (c) Faraday (d) Goldstein

The frequency of an electromagnetic radiation which makes \(2 \times 10^{6}\) waves per \(50 \mathrm{~cm}\) is (a) \(1.2 \times 10^{15} \mathrm{~Hz}\) (b) \(150 \mathrm{~Hz}\) (c) \(6 \times 10^{14} \mathrm{~Hz}\) (d) \(1.2 \times 10^{13} \mathrm{~Hz}\)

A certain laser transition emits \(6.0 \times 10^{15}\) quanta per sec per square metre of \(\lambda=662.6 \mathrm{~nm} .\) What is the power output in joule per sec per square metre? (a) \(1.8 \times 10^{-3}\) (b) \(6.626 \times 10^{-4}\) (c) \(1.8 \times 10^{3}\) (d) \(6.626 \times 10^{-12}\)

A bulb emits light of wavelength \(\frac{1987.8}{7} \mathrm{~nm} .\) The bulb is rated as \(200 \mathrm{~W}\) and \(14 \%\) of the energy is emitted as light. How many photons are emitted by the bulb per second? (a) \(1.2 \times 10^{21}\) (b) \(4 \times 10^{10}\) (c) \(1.33 \times 10^{11}\) (d) \(4 \times 10^{19}\)

The dye acriflavine when dissolved in water has its maximum light absorption at \(4530 \AA\) and has maximum florescence emission at \(5080 \AA\). The number of fluorescence quanta is about \(53 \%\) of the number of quanta absorbed. What percentage of absorbed light energy is emitted as fluorescence? (a) \(41 \%\) (b) \(47 \%\) (c) \(74 \%\) (d) \(63 \%\)

Which of the following is incorrect statement? (a) Cathode rays are emitted out from the surface of cathode. (b) Cathode rays travel in straight line. (c) Anode rays are heavier than cathode rays. (d) Anode rays are emitted out from the surface of anode.

The vapours of \(\mathrm{Hg}\) absorb some electron accelerated by a potential difference of \(5.0 \mathrm{~V}\) as a result of which light is emitted. If the full energy of single incident electron is supposed to be converted into light emitted by single Hg-atom, the wavelength of the emitted light is (a) \(2480 \mathrm{~nm}\) (b) \(248 \mathrm{~nm}\) (c) \(6200 \mathrm{~nm}\) (d) \(620 \mathrm{~nm}\)

A ruby laser produces radiations of wavelength \(662.6 \mathrm{~nm}\) in pulses whose duration are \(1.0 \times 10^{-9} \mathrm{~s}\). If the laser produces \(0.36 \mathrm{~J}\) of energy per pulse, how many photons are produced in each pulse? (a) \(1.2 \times 10^{9}\) (b) \(1.2 \times 10^{27}\) (c) \(1.2 \times 10^{18}\) (d) \(1.2 \times 10^{15}\)

In an oil drop experiment, the following charges (in arbitrary units) were found on a series of oil droplets: \(4.5 \times 10^{-18}\), \(3.0 \times 10^{-18}, 6.0 \times 10^{-18}, 7.5 \times 10^{-18}\) \(9.0 \times 10^{-18}\). The charge on electron (in the same unit) should be (a) \(3.0 \times 10^{-18}\) (b) \(9.0 \times 10^{-18}\) (c) \(1.5 \times 10^{-18}\) (d) \(1.6 \times 10^{-19}\)

\(\mathrm{O}_{2}\) undergoes photochemical dissociation into one normal oxygen atom and one oxygen atom, \(1.2 \mathrm{eV}\) more energetic than normal. The dissociation of \(\mathrm{O}_{2}\) into two normal atoms of oxygen requires \(482.5 \mathrm{~kJ} / \mathrm{mol} .\) The maximum wavelength effective for photochemical dissociation of \(\mathrm{O}_{2}\) is \((1 \mathrm{eV}=96.5 \mathrm{~kJ} / \mathrm{mol})\) (a) \(248 \mathrm{~nm}\) (b) \(1033.3 \mathrm{~nm}\) (c) \(1236.2 \mathrm{~nm}\) (d) \(200 \mathrm{~nm}\)

In Wilson cloud chamber experiment, two particles were found to show equal deviations but in opposite directions. The names positron and negatron were given to these particles by Anderson. Hence, Negatron is (a) neutron (b) neutrino (c) proton (d) electron

Photo-dissociation of water \(\mathrm{H}_{2} \mathrm{O}(\mathrm{I})+h v\) \(\rightarrow \mathrm{H}_{2}(\mathrm{~g})+1 / 2 \mathrm{O}_{2}(\mathrm{~g})\) has been suggested as a source of hydrogen. The heat absorbed in this reaction is \(289.5 \mathrm{~kJ} / \mathrm{mole}\) of water decomposed. The maximum wavelength that would provide the necessary energy assuming that one photon causes the dissociation of one water molecule is \((1 \mathrm{eV}=96.5 \mathrm{~kJ} / \mathrm{mol})\) (a) \(413.33 \mathrm{~nm}\) (b) \(826.67 \mathrm{~nm}\) (c) \(206.67 \mathrm{~nm}\) (d) \(4.3 \mathrm{~nm}\)

Which of the following particle is not deflected in the magnetic field? (a) Electron (b) Proton (c) Neutron (d) Deuteron

Which of the following particle have non zero \(e / m\) ratio? (a) Neutron (b) Neutrino (c) Positron (d) Neutral meson

In a measurement of the quantum efficiency of photosynthesis in green plants, it was found that 9 quanta of red light at \(6900 \AA\) Å were needed to evolve 1 molecule of \(\mathrm{O}_{2}\). The average energy storage in the photosynthesis process is \(111.6 \mathrm{kcal} /\) mol of \(\mathrm{O}_{2}\) evolved. What is the energy conversion efficiency in this experiment? \(\left(\frac{h \cdot c}{e}=1.24 \times 10^{-7} \mathrm{~nm} . \mathrm{eV}, 1 \mathrm{eV}=23 \mathrm{kcal} / \mathrm{mol}\right)\) (a) \(70 \%\) (b) \(50 \%\) (c) \(40 \%\) (d) \(30 \%\)

For a photochemical reaction, \(\mathrm{A} \rightarrow \mathrm{B}\), \(1 \times 10^{-5}\) moles of 'B' were formed on absorption of \(6.626 \times 10^{7}\) erg at \(360 \mathrm{~nm}\). The quantum efficiency (molecules of ' \(\mathrm{B}\) ' formed per photon) is (a) \(1.0\) (b) \(0.25\) (c) \(0.5\) (d) \(2.0\)

The potential difference between cathode and anode in a cathode ray tube is \(V\). The speed acquired by the electrons is proportional to (a) \(V\) (b) \(\sqrt{V}\) (c) \(V^{2}\) (d) \(1 / \sqrt{V}\)

Light of wavelength, \(\lambda\), falls on a metal having work function \(h c / \lambda_{0} .\) Photoelectric effect will take place only if (a) \(\lambda \geq \lambda_{0}\) (b) \(\lambda \geq 2 \lambda_{0}\) (c) \(\lambda \leq \lambda_{0}\) (d) \(\lambda \leq \lambda_{0} / 2\)

The ratio of specific charges of \(\alpha\) -particle and deuteron is (a) \(1: 2\) (b) \(2: 1\) (c) \(1: 1\) (d) \(4: 1\)

Light of wavelength, \(\lambda\), strikes a metal surface with intensity \(X\) and the metal emits \(Y\) electrons per second of maximum kinetic energy \(Z\). What will happen to \(Y\) and \(Z\) if \(X\) is halved? (a) \(Y\) will be halved and \(Z\) will be doubled (b) \(Y\) will be doubled and \(Z\) will be halved (c) \(Y\) will be halved and \(Z\) will remain the same (d) \(Y\) will remain same and \(Z\) will be halved

\(e / m\) ratio of a particle of charge 2 unit and mass 4 amu is (a) \(4.8 \times 10^{7} \mathrm{C} / \mathrm{kg}\) (b) \(0.5 \mathrm{C} / \mathrm{kg}\) (c) \(4.8 \times 10^{4} \mathrm{C} / \mathrm{kg}\) (d) \(8 \times 10^{-20} \mathrm{C} / \mathrm{kg}\)

Photoelectric emission is observed from a metal surface for frequencies \(v_{1}\) and \(v_{2}\) of the incident radiation \(\left(v_{1}>v_{2}\right)\). If maximum kinetic energies of the photoelectrons in the two cases are in the ratio \(1: K\), then the threshold frequency for the metal is given by (a) \(\frac{v_{2}-v_{1}}{K-1}\) (b) \(\frac{K v_{2}-v_{1}}{K-1}\) (c) \(\frac{K v_{1}-v_{2}}{K}\) (d) \(\frac{K v_{1}-v_{2}}{K-1}\)

Atoms have void spaces. It was first suggested by (a) Rutherford (b) Thomson (c) Lenard (d) Dalton

Rutherford's experiment, which established the nuclear model of the atom, used a beam of (a) \(\beta\) -particles, which impinged on a metal foil and got absorbed. (b) \(\gamma\) -rays, which impinged on a metal foil and ejected electrons. (c) helium atoms, which impinged on a metal foil and got scattered. (d) helium nuclei, which impinged on a metal foil and got scattered.

If \(\lambda_{0}\) is the threshold wavelength for photoelectric emission from a metal surface, \(\lambda\) is the wavelength of light falling on the surface of metal and \(m\) is the mass of electron, then the maximum speed of ejected electrons is given by (a) \(\left[\frac{2 h}{m}\left(\lambda_{0}-\lambda\right)\right]^{1 / 2}\) (b) \(\left[\frac{2 h c}{m}\left(\lambda_{0}-\lambda\right)\right]^{1 / 2}\) (c) \(\left[\frac{2 h c}{m}\left(\frac{\lambda_{0}-\lambda}{\lambda_{0} \lambda}\right)\right]^{1 / 2}\) (d) \(\left[\frac{2 h}{m}\left(\frac{1}{\lambda_{0}}-\frac{1}{\lambda}\right)\right]^{1 / 2}\)

Which of the following is not a correct statement according to Rutherford's atomic model? (a) \(99 \%\) of mass of an atom is centred in the nucleus. (b) Most of the part inside the atom is empty. (c) The size of nucleus is very small in comparison to the atoms. (d) Electrons revolve round the nucleus.

When \(\beta\) -particles are sent through a tin metal foil, most of them go straight through the foil as (a) \(\beta\) -particles are much heavier than electron (b) most part of the atom is empty space (c) \(\beta\) -particles are positively charged (d) \(\beta\) -particles moves with high velocity

Two carbon discs, \(1.0 \mathrm{~g}\) each, are \(1.0 \mathrm{~cm}\) apart have equal and opposite charges. If force of attraction between them is \(10^{-5} \mathrm{~N}\), the ratio of excess electrons to the total atoms on the negatively charged disc is \(\left(N_{\mathrm{A}}=6 \times 10^{23}\right)\) (a) \(2.4 \times 10^{-12}: 1\) (b) \(10^{-12}: 2.4\) (c) \(10^{12}: 2.4\) (d) \(2.4: 10^{12}\)

The radius of the hydrogen atom in its ground state is \(5.3 \times 10^{-11} \mathrm{~m}\). After collision with an electron it is found to have a radius of \(21.2 \times 10^{-11} \mathrm{~m} .\) The principal quantum number of final state of the atom is (a) 2 (b) 3 (c) 4 (d) 16

Two particles, \(\mathrm{A}\) and \(\mathrm{B}\), having same \(e / \mathrm{m}\) ratio are projected towards silver nucleus, in different experiments, with the same speed. The distance of closest approach will be (a) same for both (b) greater for A (c) greater for \(\mathrm{B}\) (d) depends on speed

For which orbit in \(\mathrm{He}^{+}\) ion, the circumference is \(26.5 \AA\) ? (a) 2 (b) 3 (c) 4 (d) 16

\(\alpha\) -particles are projected towards the nucleus of following metals, with the same kinetic energy. Towards which metal, the distance of closest approach will be minimum? (a) \(\operatorname{Cu}(Z=29)\) (b) \(\operatorname{Ag}(Z=47)\) (c) \(\mathrm{Au}(Z=79)\) (d) \(\mathrm{Ca}(Z=20)\)

The radius of the second orbit of \(\mathrm{H}\) -atom is equal to the radius of (a) second orbit of \(\mathrm{He}^{+}\) ion (b) third orbit of \(\mathrm{Li}^{2+}\) ion (c) fourth orbit of \(\mathrm{He}^{+}\) ion (d) fourth orbit of \(\mathrm{Be}^{3+}\) ion

The ratio of the areas within the electron orbits for the first excited state to the ground state for the hydrogen atom is (a) \(2: 1\) (b) \(4: 1\) (c) \(8: 1\) (d) \(16: 1\)

If nucleus and atom are considered as perfect spheres with the diameters \(4 \times 10^{15} \mathrm{~m}\) and \(2 \times 10^{-10} \mathrm{~m}\), respectively, then the ratio of the volumes of nucleus and atom should be (a) \(2 \times 10^{-5}: 1\) (b) \(8 \times 10^{-15}: 1\) (c) \(1.25 \times 10^{14}: 1\) (d) \(8 \times 10^{15}: 1\)

What is the distance travelled by an electron revolving in the second orbit of \(\mathrm{Be}^{3+}\) ion, in 100 revolutions? (a) \(3.32 \times 10^{-8} \mathrm{~m}\) (b) \(5.29 \times 10^{-8} \mathrm{~m}\) (c) \(6.64 \times 10^{-8} \mathrm{~m}\) (d) \(1.16 \times 10^{-8} \mathrm{~m}\)

Which of the following cannot be circumference of an orbit in H-atom? \(\left(r_{0}=\right.\) radius of the first orbit \()\) (a) \(2 \pi r_{0}\) (b) \(4 \pi r_{0}\) (c) \(8 \pi r_{0}\) (d) \(18 \pi r_{0}\)

Small packets of light is called (a) proton (b) quanta (c) photon (d) spectrum

In the Bohr's atomic model, the electrostatic force of attraction between nuclear charge \(\left(Z_{\mathrm{e}}\right)\) and electron of charge \(e\) is balanced by the centripetal force acting towards the centre of atom. If \(\epsilon_{0}\) be the permittivity of vacuum and \(r\) be the radius of orbit in which electron is revolving, the speed of electron is (a) \(\sqrt{\frac{Z e^{2}}{\left(4 \pi \varepsilon_{0}\right) m r}}\) (b) \(\sqrt{\frac{\left(4 \pi \varepsilon_{0}\right) m r}{Z e^{2}}}\) (c) \(\sqrt{\left(4 \pi \varepsilon_{\mathrm{o}}\right) m r Z e^{2}}\) (d) \(\frac{e}{\sqrt{\left(4 \pi \varepsilon_{\mathrm{o}}\right) m r}}\)

Which of the following electromagnetiradiation have greater frequency? (a) X-rays (b) Ultraviolet rays (c) Radio waves (d) Visible rays

As its closest approach, the distance between the Mars and the Earth is found to be 60 million \(\mathrm{km}\). When the planets are at this closest distance, how long would it take to send a radio massage from a space probe of Mars of Earth? (a) \(5 \mathrm{~s}\) (b) \(200 \mathrm{~s}\) (c) \(0.2 \mathrm{~s}\) (d) \(20 \mathrm{~s}\)

Two electromagnetic radiations have wave numbers in the ratio \(2: 3\). Their energies per quanta will be in the ratio (a) \(3: 2\) (b) \(9: 4\) (c) \(4: 9\) (d) \(2: 3\)

The time period of revolution of electron in H-atom is directly proportional to (a) \(r\) (b) \(r^{1 / 2}\) (c) \(r^{3 / 2}\) (d) \(r^{2}\)

The eyes of a certain member of the reptile family pass a single visual single to the brain when the visual receptors are stuck by photons of wavelength \(662.6 \mathrm{~nm}\). If a total energy of \(3.0 \times 10^{-14} \mathrm{~J}\) is required to trap the signal, what is the minimum number of photons that must strike the receptor? (a) \(1.0 \times 10^{5}\) (b) \(1.0 \times 10^{6}\) (c) 1000 (d) 1