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The anode of a thermionic diode is connected to the negative terminal of a battery and the cathode to its positive terminal.
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The constant A in the Richardson−Dushman equation for tungsten is 60 × 104 A m−2K−2. The work function of tungsten is 4.5 eV. A tungsten cathode with a surface area 2.0 × 10−5 m2 is heated by a 24 W electric heater. In steady state, the heat radiated by the heater and the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan's Constant = 6 × 10−8 W m−2 K−1. Assume that the thermions take only a small fraction of the heat supplied.
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Explain the terms : Transmitter in communication system
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Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
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Asha's mother read an article in the newspaper about a disaster that took place at Chernobyl. She could not understand much from the articles and asked a few questions from Asha regarding the article. Asha tried to answer her mother's questions based on what she learnt in Class XII Physics.
(a) What was the installation at Chernobyl where the disaster took place? What according to you, was the cause of this disaster?
(b) Explain the process of release of energy in the installation at Chernobyl.
(c) What according to you, were the values displayed by Asha and her mother?
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Distinguish between a conductor, a semiconductor and an insulator on the basis of energy band diagrams.
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The wavefronts of a light wave travelling in vacuum are given by x + y + z = c. The angle made by the direction of propagation of light with the X-axis is _________ .
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The wavefronts of light coming from a distant source of unknown shape are nearly _________ .
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Calculate the electric field in a copper wire of cross-sectional area 2.0 mm2 carrying a current of 1 A.
The resistivity of copper = 1.7 × 10–8 Ω m
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A wire has a length of 2.0 m and a resistance of 5.0 Ω. Find the electric field existing inside the wire if it carries a current of 10 A.
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Consider the situation shown in figure (31-E29). The width of each plate is b. The capacitor plates are rigidly clamped in the laboratory and connected to a battery of emf ε. All surfaces are frictionless. Calculate the value of M for which the dielectric slab will stay in equilibrium.
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The susceptibility of magnesium at 300 K is 1.2 × 10−5. At what temperature will the susceptibility increase to 1.8 × 10−5?
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A metallic loop is placed in a nonuniform magnetic field. Will an emf be induced in the loop?
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An inductor is connected to a battery through a switch. Explain why the emf induced in the inductor is much larger when the switch is opened as compared to the emf induced when the switch is closed.
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Figure shows a horizontal solenoid connected to a battery and a switch. A copper ring is placed on a frictionless track, the axis of the ring being along the axis of the solenoid. As the switch is closed, the ring will __________ .
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How many 1s energy states are present in one mole of sodium vapour? Are they all filled in normal conditions? How many 3s energy states are present in one mole of sodium vapour? Are they all filled in normal conditions?
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There are energy bands in a solid. Do we have really continuous energy variation in a band ro do we have very closely spaced but still discrete energy levels?
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The conduction band of a solid is partially filled at 0 K. Will it be a conductor, a semiconductor or an insulator?
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In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band. Why does the number of conduction electrons not go on increasing with time as thermal collisions continuously take place?
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When an electron goes from the valence band to the conduction band in silicon, its energy is increased by 1.1 eV. The average energy exchanged in a thermal collision is of the order of kT which is only 0.026 eV at room temperature. How is a thermal collision able to take some to the electrons from the valence band to the conduction band?
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