Light travels in a straight line (rectilinear propagation of light). This statement does hold if the medium of travel for light is
- A.of variable refractive index
- B.made up of slabs of different refractive indices
- C.homogeneous and transparent
- D.inhomogeneous and transparent
Correct answer
Explanation
The correct answer is C, homogeneous and transparent. Light keeps to a straight line only while its speed stays the same, which happens in a homogeneous, transparent medium.
The speed of light in a medium is set by its refractive index. If the index is the same everywhere, as in still air, pure water or a uniform block of glass, light has no reason to bend and travels straight. This is why shadows have sharp edges and why a pinhole camera forms an image. When light passes into a region of different refractive index, it changes speed and bends; this bending is refraction.
A is wrong because a changing refractive index bends light gradually, as in a mirage over a hot road. B is wrong because light bends at every boundary between slabs of different indices. D is wrong because an inhomogeneous medium also changes the speed of light from place to place and so curves its path.
Exam tip: Rectilinear propagation needs a homogeneous, transparent medium; a change in refractive index means refraction, as in mirages.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
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- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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