An electron gun typically includes a filament, cathode, control grid and anodes; the OCR shows option A as selected.
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A swimmer is swimming inside a tank of water. He looks up at the sky through the water surface. The surface is calm. Sky is bright due to daylight. He can see
This is Snell's window: refraction at the water surface limits the sky to a circular patch whose angular extent depends only on refractive index, not on depth.
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A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will
If lens and surrounding medium have the same refractive index, there is no refraction at surfaces and the lens has no optical power, so focal length is infinite.
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Four optical media have indices of refraction 1.40, 1.50, 1.60 and 1.70 respectively. The medium that has the largest critical angle is the one whose index of refraction is
Critical angle is largest when refractive index is smallest; among given values 1.40 is smallest.
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The velocity of light in glass (whose refractive index with respect to air is 1.5) is 2 × 10^8 m/sec. In a certain liquid the velocity of light is found to be 2.5 × 10^8 m/sec. The refractive index of the liquid with respect to air is
Powers of thin lenses in contact add: +2 D + (-4 D) = -2 D, so the combined power is -2 D.
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Light of wavelength 500 nm travelling with speed 2.0 × 10^8 m s^-1 in a certain medium enters another medium whose refractive index is 5/4 times that of the first medium. What are the wavelength and speed in the second medium?
Blocking half the lens reduces the amount of light but rays from the whole object still pass through remaining portions, producing the full image with lower intensity.
