Physics - Electrons and Protons
Exam Duration: 45 Mins Total Questions : 30
The specific charge of electron is
- (a)
\(1.6\times10^{-19}C\)
- (b)
\(9.1 \times10^{-31}kg\)
- (c)
\(1.76\times10^{11}C kg^{-1}\)
- (d)
\(5.7\times10^{-12}kg C^{-1}\)
Gases begin to conduct electricity at low pressure because
- (a)
The electrons in atoms can move freely at-low pressure
- (b)
Atoms break up into electrons and protons
- (c)
Colliding electrons can acquire higher kinetic energy due to increased mean free path causing ionisation of atoms
- (d)
At low pressure gas turn into plasma
Proton is 1840 times heavier than an electron. The ratio of specific charge of \(\alpha \)-particle to that of electron is
- (a)
1840
- (b)
\((1840)^{-1}\)
- (c)
\((3680)^{-1}\)
- (d)
3680
Energy of an electron can be increased by
- (a)
making them fall from a great height
- (b)
moving them through an electric potential
- (c)
passing them through lead block
- (d)
passing them through high magnetic field
The path of moving electron is a parabola if electron has
- (a)
no initial velocity in a direction different from that of an electric field
- (b)
an initial velocity perpendicular to direction of an electric field
- (c)
Both (a) and (b) are true
- (d)
Both (a) and (b) are not true
Which one of the following statements about photon is NOT CORRECT ?
- (a)
Photons exert no pressure.
- (b)
Photon's energy is \(h\upsilon \).
- (c)
Photon's momentum is \(h\upsilon /c\).
- (d)
Photon's rest mass is zero.
The resistance of a discharge tube at a very low pressure is
- (a)
zero
- (b)
ohmic
- (c)
approaching infinity
- (d)
non-ohmic
In a dischange tube at 0.02 mm, there is formation of
- (a)
Faraday's dark space
- (b)
Crooke's dark space
- (c)
Both spaces partly
- (d)
Crooke's dark space with glow near the electrodes
An electron starts from rest in an electric field and acquired a speed u in reaching a point A. The potential difference between the starting point and the point A is \(V_{A}\). The u is proportional to
- (a)
\(V^{2}_{A}\)
- (b)
\(V_{A}\)
- (c)
\(\sqrt {V_{A}}\)
- (d)
\((V_{A})^{2/3}\)
A proton, a deutron and an \(\alpha \)- particle have same kinetic energies. Their velocities are in the ratio of
- (a)
\(1 : \sqrt2 : 1\)
- (b)
\(1 : 1 : \sqrt2\)
- (c)
\(\sqrt2 : 1 : 1\)
- (d)
\(1 : {1\over\sqrt2} : 1\)
An electron beam at rest is accelerated in a uniform electric field of strength E. The kinetic energy attained by it as it travels through a distance x is
- (a)
\(x\over E_{e}\)
- (b)
\(x Ee\)
- (c)
\(Ee\over x\)
- (d)
\(xe\over E\)
Doubly ionised helium atoms and hydrogen ions are accelerated through the same potential. The ratio of the final velocities of helium and of the hydrogen ions is
- (a)
2
- (b)
\(\sqrt2\)
- (c)
\(1\over2\)
- (d)
\(1\over\sqrt2\)
In a discharge tube, at a pressure of 0.02 mm there is a formation of
- (a)
Faraday's dark space
- (b)
Crooke's dark space
- (c)
both spaces partly
- (d)
Crooke's dark space with glow near electrodes
A current in an electron beam of a cathode ray tube is 4.8 mA. If an accelerating voltage is 2000 V, then the number of electrons striking the screen each second is (charge on electron = \(1.6 \ \times \ 10^{-19} \ C\))
- (a)
\(3 \times 10^{16}\) and kinetic energy, \(E_{k}\), of each electron is \(3.2 \times10^{-16}J\)
- (b)
\(6 \times 10^{6}\) and \(E_{k}\) is \(3.2 \times10^{-16}J\)
- (c)
\(3 \times 10^{18}\) and \(E_{k}\) is \(1.6 \times10^{-14}J\)
- (d)
None of the above
The distance between the two places of a cathode-ray oscilloscope is 1 cm and potential difference between them is 1200 volt. If an electron of energy 2000 eV enters at right angles to the field, what will be its enters at right angles to the field, what will be its deflection if the plate be 1.5 cm long ?
- (a)
0.34 cm
- (b)
0.34 cm
- (c)
3.4 cm
- (d)
34 cm
In a Thomson's experiment for e/m, the same high tension d.c. supply provides potential to the anode of the accelerating column, as also to the positive deflecting plate in the region of crossed fields. If the supply voltage is doubled, by what factor should the magnetic field be changed to keep the electron beam undeflected ?
- (a)
142% increase
- (b)
42% decrease
- (c)
142% decrease
- (d)
42% increase
Photoelectric effect is an indirect evidence of
- (a)
wave theory of light
- (b)
quantum theory of light
- (c)
corpuscular theory of light
- (d)
electromagnetic wave theory of light
Radition include energy travelling in the form of
- (a)
waves only
- (b)
particles only
- (c)
both waves and particles
- (d)
quanta of energy
Diffraction of electron confirms that
- (a)
particles behave like waves
- (b)
particles have independent character
- (c)
waves show particle properties
- (d)
None of the above
The wavelength of \(K_{\alpha }\) line from an element of atomic number 41 is \(\lambda \). Then, the wavelength of \(K_{\alpha }\) line of an element of atomic number 21 is
- (a)
\(4??\lambda \)
- (b)
\(\lambda /4\)
- (c)
3.08\(\lambda \)
- (d)
0.26 \(\lambda \)
The shortest wavelenght of X-ray emitted from an X-ray tube depends on
- (a)
the current in the tube
- (b)
the voltage applied to the tube
- (c)
the nature of the gas in the tube
- (d)
the atomic number of the target material
The work function of a photoelectric material is 3.3eV. Its threshold frequency will be
- (a)
\(8\times10^{14}Hz\)
- (b)
\(5\times10^{33}Hz\)
- (c)
\(8\times10^{10}Hz\)
- (d)
\(4\times10^{11}Hz\)
Photo-electric effect supports the quantum nature of light because
- (a)
there is a minimum frequency of light below which no photo electrons are emitted
- (b)
the maximum kinetic energy of photo-electrons depends only on the frequency of light and not on its intensity
- (c)
even when the metal surface is faintly illuminated, the photoelectrons leave the surface immediately
- (d)
All of the above
In a photoelectric experiment, the stopping potential \(V_{s}\) is plotted against the frequancy \(\upsilon \), of the incident light. The resulting curve is a straight line which makes an angle \(\theta \) with the \(\upsilon \)-axis. Then tan \(\theta \) is equal to
- (a)
h/e
- (b)
e/h
- (c)
\(-\phi \)/e
- (d)
\(eh/\phi \)
The wavelength associated with a gold ball weighing 200 g and moving at a speed of 5 m/h is of the order of (h=6.626\(\times10^{-34} Js\)).
- (a)
\(10^{-10} m\)
- (b)
\(10^{-20} m\)
- (c)
\(10^{-30} m\)
- (d)
\(10^{-40} m\)
A light of inrensity \(I_{0}\) passes through a material of thickness d. The resultant intensity is
- (a)
\(I=I_{0}(1-e^{-\lambda d})\)
- (b)
\(I=I_{0}e^{-\lambda d}\)
- (c)
\(I=I_{0}e^{\lambda d}\)
- (d)
\(I=I_{0}(1-e^{-d/h})\)
Light of wavelength 2000 \(\mathring { A } \) falls on aluminium surface. In aluminium 4.2 eV are requried to remove an eletron.
A. Kinetic energy of the fastest emitted photoelectrons is 2. eV
B. Kinetic energy of the slowest emitted photoelectrons is 2 eV
C. Stopping potential for aluminium is 2 V
D. Cutt off wavelength for aluminium is 3000 \(\mathring { A } \)
Mark :
- (a)
If A is correct only
- (b)
if B is correct only
- (c)
if A and C correct only
- (d)
if A, C and D are correct only
The wavelength of incident light falling on a photosensitive surface is changed from 2000 \(\mathring { A } \) to 2100 \(\mathring { A } \). The corresponding change in stopping potential is
- (a)
0.03 V
- (b)
0.3 V
- (c)
3 V
- (d)
3.3 V
The de Brogile wavelength \(\lambda \) of an electron in the \(n^{th}\) Bohr orbit is related to the radius R of the orbit as
- (a)
\(\lambda ={\pi R\over n}\)
- (b)
\(\lambda ={3\pi R\over 2n}\)
- (c)
\(\lambda ={2\pi R\over n}\)
- (d)
\(\lambda ={4\pi R\over n}\)