Why are danger signals typically red in colour?
- A.Red light has a longer wavelength and is scattered the least, making it visible from a distance.
- B.Red light is more reflective than other colours.
- C.Red light is easier to produce artificially.
- D.The colour red is aesthetically pleasing.
Correct answer
Explanation
The correct answer is A, Red light has a longer wavelength and is scattered the least, making it visible from a distance. Red has the longest wavelength in visible light, about 700 nm, so the tiny particles of air, fog, smoke and dust scatter it the least. The light therefore travels far without fading and can be seen from a distance, which is exactly what a danger signal needs. This follows Rayleigh scattering: the shorter the wavelength, the more the light is scattered. The same idea explains why the clear sky looks blue, since blue light is scattered the most, and why the sun looks red at sunrise and sunset. B is wrong because red light is not more reflective than other colours. C is wrong because how easily a colour is produced has nothing to do with its use in signals. D is wrong because looks are not the scientific reason. Exam tip: longest wavelength = least scattering = red for danger; shortest wavelength = most scattering = blue sky.
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?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- 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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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
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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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- 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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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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