Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
Correct answer
Explanation
The correct answer is D, total internal reflection of light. Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Diamond has a very high refractive index, about 2.42, so its critical angle is very small, only about 24°. Any ray striking an inner face at more than this angle cannot leave and is totally reflected back into the stone. Jewellers cut diamonds with many facets at carefully chosen angles so that light entering through the top is trapped by repeated total internal reflection and comes out only through the crown, bright and concentrated. The high refractive index also spreads white light into colours, which adds to the fire of the stone.
A is wrong: interference causes the colours of soap bubbles and oil films, not a diamond's brilliance.
B is wrong: diffraction is the bending of light round small obstacles and openings.
C is wrong: polarization restricts the vibrations of light to one plane and plays no part here.
Exam tip: diamond sparkle, mirage, optical fibres and the shining of an air bubble in water all come from total internal reflection.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
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An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
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Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
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Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
Read the full explanation →The frequency of ultrasound waves is
- A.less than 20 Hz
- B.between 20 Hz and 2 kHz
- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
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Ultrasound is sound with a frequency above 20,000 Hz, the upper limit of human hearing. Humans hear sound between about 20 Hz and 20 kHz.
Read the full explanation →