Two plane mirrors are placed perpendicular to each other. A ray strikes one mirror and after reflection falls on the second mirror. The ray after reflection from the second mirror will be:
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Two successive reflections from perpendicular mirrors produce a net deviation of 180°.
The distance between an object and its real image formed by a convex lens cannot be:
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For a real image, the minimum object-image separation is 4f.
The index of refraction of diamond is 2.0. Velocity of light in diamond in cm s⁻¹ is approximately:
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v = c/n = 3×10¹⁰/2 cm s⁻¹.
For an astronomical telescope fo + fe = 105 cm, and magnification is 20. Focal lengths of objective and eyepiece are:
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For normal adjustment, magnification = fo/fe and length = fo + fe.
A monochromatic beam of light passes from a denser to a rarer medium. As a result, its:
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Light travels faster in a rarer medium; frequency remains unchanged.
To increase the magnification of a telescope:
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Telescope magnifying power in normal adjustment is fo/fe.
The power of a lens is 4 diopters. Its focal length is:
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P = 1/f when f is in metres.
When light passes from one medium to another, the physical quantity that remains unchanged is:
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The frequency is determined by the source and does not change at a boundary.
An object is placed between two parallel mirrors. The number of images formed is:
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Repeated reflections continue indefinitely between parallel mirrors.
An astronomical telescope has an angular magnification of magnitude 5 for distant objects. The separation between the objective and the eyepiece is 36 cm and the final image is formed at infinity. The focal lengths are:
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For normal adjustment, fo + fe = 36 and fo/fe = 5.
A diver in a lake wants to signal his distress to a person sitting on the edge of the lake by flashing his waterproof torch. He should direct the beam:
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The beam must emerge into the air; the incidence angle must be below the critical angle.
The figure shows an equiconvex lens of focal length f. If the lens is cut along PQ, the focal length of each half will be:
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Cutting perpendicular to the principal axis produces a plano-convex half; its focal length doubles.
A compound microscope has a magnification of 30. The focal length of the eye-piece is 5 cm. If the final image is formed at the least distance of distinct vision (25 cm), the magnification produced by the objective is:
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Eyepiece magnification = 1 + D/fe = 6; objective magnification = 30/6 = 5.
A ray of light travels from air to glass as shown in the figure. The speed of light in air is 3.0×10⁸ m/s. What is the speed of light in glass?
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Using Snell's law with incidence 45° and refraction 30° gives n ≈ 1.414, so v ≈ 2.12×10⁸ m/s.
Distance of distinct vision is 25 cm. The focal length of the convex lens is 5 cm. It can act as a magnifier of magnifying power:
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For a simple magnifier with final image at the near point, M = 1 + D/f = 6.
Which of the following produce a virtual image larger in size than the object?
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A convex lens produces a virtual magnified image when the object is placed within its focal length.
For normal adjustment, length of astronomical telescope is:
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In normal adjustment, the final image is at infinity and tube length is fo + fe.
Total internal reflection of a ray of light is possible when the ray goes from:
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TIR requires travel from optically denser to rarer medium with incidence angle greater than the critical angle.
The least distance of distinct vision is 22.5 cm. The focal length of a convex lens is 7.5 cm. It can act as a simple microscope of magnifying power:
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M = 1 + D/f = 1 + 22.5/7.5 = 4.
What is the time taken by light to travel 4 mm in a material of refractive index 3?
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Use v = c/n and t = distance/velocity.
