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The plate current in a triode value is maximum when the potential of the grid is ______________ .
Concept: undefined >> undefined
Electric conduction takes place in a discharge tube due to the movement of _____________ .
(a) positive ions
(b) negative ions
(c) electrons
(d) protons
Concept: undefined >> undefined
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Which of the following is true for a cathode ray?
(a) It travels in a straight line.
(b) It emits an X-ray when it strikes a metal.
(c) It is an electromagnetic wave.
(d) It is not deflected by a magnetic field.
Concept: undefined >> undefined
Due to the space charge in a diode valve, _____________ .
Concept: undefined >> undefined
The saturation current in a triode valve can be changed by changing _____________ .
Concept: undefined >> undefined
The plate current in a diode is zero. It is possible that _____________ .
(a) the plate voltage is zero
(b) the plate voltage is slightly negative
(c) the plate voltage is slightly positive
(d) the temperature of the filament is low
Concept: undefined >> undefined
The plate current in a triode valve is zero. The temperature of the filament is high. It is possible that ____________ .
(a) Vg > 0, Vp > 0
(b) Vg > 0, Vp < 0
(c) Vg < 0, Vp > 0
(d) Vg < 0, Vp < 0
Concept: undefined >> undefined
A discharge tube contains helium at low pressure. A large potential difference is applied across the tube. Consider a helium atom that has just been ionised due to the detachment of an atomic electron. Find the ratio of the distance travelled by the free electron to that by the positive ion in a short time dt after ionisation.
Concept: undefined >> undefined
A molecule of a gas, filled in a discharge tube, gets ionised when an electron is detached from it. An electric field of 5.0 kV m−1 exists in the vicinity of the event. (a) Find the distance travelled by the free electron in 1 µs, assuming there's no collision. (b) If the mean free path of the electron is 1.0 mm, estimate the time of transit of the free electron between successive collisions.
Concept: undefined >> undefined
The mean free path of electrons in a gas in a discharge tube is inversely proportional to the pressure inside it. The Crookes dark space occupies half the length of the discharge tube when the pressure is 0.02 mm of mercury. Estimate the pressure at which the dark space will fill the whole tube.
Concept: undefined >> undefined
Two discharge tubes have identical material structures and the same gas is filled in them. The length of one tube is 10 cm and that of the other tube is 20 cm. Sparking starts in both the tubes when the potential difference between the cathode and the anode is 100 V. If the pressure in the shorter tube is 1.0 mm of mercury, what is the pressure in the longer tube?
Concept: undefined >> undefined
The saturation current from a thoriated-tungsten cathode at 2000 K is 100 mA. What will be the saturation current for a pure-tungsten cathode of the same surface area operating at the same temperature? The constant A in the Richardson-Dushman equation is 60 × 104 Am −2 K−2 for pure tungsten and 3.0 × 104 Am −2 k−2 for thoriated tungsten. The work function of pure tungsten is 4.5 eV and that of thoriated tungsten is 2.6 eV.
Concept: undefined >> undefined
The plate current in a triode can be written as \[i_p = k \left( V_g + \frac{V_p}{\mu} \right)^{3/2}\] Show that the mutual conductance is proportional to the cube root of the plate current.
Concept: undefined >> undefined
An a-particle and a proton of the same kinetic energy are in turn allowed to pass through a magnetic field `vec"B"`, acting normal to the direction of motion of the particles. Calculate the ratio of radii of the circular paths described by them.
Concept: undefined >> undefined
Answer the following question.
Under what conditions is the phenomenon of total internal reflection of light observed? Obtain the relation between the critical angle of incidence and the refractive index of the medium.
Concept: undefined >> undefined
Answer the following question.
Three lenses of focal length +10 cm, —10 cm and +30 cm are arranged coaxially as in the figure given below. Find the position of the final image formed by the combination.
Concept: undefined >> undefined
Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?
Concept: undefined >> undefined
The physical quantity having SI unit NC–1m is ______.
Concept: undefined >> undefined
With the help of a ray diagram, obtain the relation between its focal length and radius of curvature.
Concept: undefined >> undefined
Find the Q-value and the kinetic energy of the emitted α-particle in the α-decay of `""_86^220"Rn"`.
Given `"m"(""_88^226"Ra")` = 226.02540 u, `"m"(""_86^222 "Rn")` = 222.01750 u,
`"m"(""_86^220 "Rn")`= 220.01137 u, `"m"(""_84^216 "Po")`= 216.00189 u.
Concept: undefined >> undefined
