Physics MCQs

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According to Newton’s law of cooling, the rate of loss of heat of a body is directly proportional to the difference between the temperature of hot body and temperature of the surroundings, provided that the difference in temperature is small enough.

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A head mirror is mostly used for examination of the ear, nose or throat. It comprises a circular concave mirror, with a small hole in the middle, and is attached to a head band. The mirror is worn over the physician’s eye of choice, with the concave mirror surface facing outwards and the hole directly over the physician’s eye, providing illumination like a ring light.

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Optical filters are devices that selectively transmit light in a particular range of wavelengths, that is, colors, while blocking the remainder. They are commonly used in photography (where some special effect filters are occasionally used as well as absorptive filters), fluorescence microscopy, spectroscopy, clinical chemistry, coloured stage lighting, etc.

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Concave mirrors are used as dental mirrors. This is because concave mirrors produce highly magnified images which are useful in obtaining larger view of teeth and gums. These mirrors enable the dentists to see the minute details of the tooth in a magnified form.

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Semiconductors are insulators at low temperatures and reasonably good conductors at higher temperatures. As temperature increases, the semiconductor material such as silicon, germanium, etc. becomes a better and better conductor compared to metallic conductor in which the resistance increases with increase in temperature.

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In the case of a conductor, there is no forbidden energy gap. The conduction and valence energy bands overlap each other. Obviously, the electrons from the valence band can freely enter the conduction energy band. Conduction energy band Overlap Valence energy band

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Graphite is a good conductor of electricity because its electrons are delocalized or free to move around. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free. It can move easily from one carbon atom to the other.

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In remote control of television receivers at home, the functioning is dependent on the infra-red rays. These rays received by the thermionic valves regulate/control the working of television.

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The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. So among the given options, visible lights has the lowest frequency, while gamma rays has the highest.

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There are two specific heats of gases- Specific Heat at Constant Pressure (Cp) and Specific Heat at Constant Volume (Cv). Heat supplied at constant pressure is used up in two ways: (a) for doing work in expansion and (b) for raising the temperature by 1o C, while at constant volume heat supplied is used only for rise of temperature. Therefore, Cp is always greater than Cv. They are related as: Cp – Cv = R/J. This relation is called Mayer’s Relation.