Which one of the following types of glasses is used for making optical instruments?
- A.Pyrex glass
- B.Soft glass
- C.Hard glass
- D.Flint glass
Correct answer
Explanation
The correct answer is D, Flint glass. Flint glass contains lead oxide, which gives it a high refractive index and clarity, so it is used for lenses and prisms of optical instruments.
Ordinary glass is mainly silica melted with soda and lime. Changing the other ingredients changes its properties. Adding lead oxide produces flint glass, also called lead glass, which bends and spreads light strongly. It is used in lenses, prisms, spectacles and cameras, and it is often paired with crown glass in achromatic lenses to cancel colour fringes. The same lead glass, cut and polished, is sold as crystal glassware because it sparkles.
A is wrong because Pyrex is a borosilicate glass that resists heat, used for laboratory and kitchen ware. B is wrong because soft glass, or soda-lime glass, is ordinary glass for windows and bottles. C is wrong because hard glass, a potash-lime glass, is used for apparatus that must stand high temperatures.
Exam tip: Flint (lead) glass for lenses and prisms, Pyrex (borosilicate) for heat, soda-lime for windows, crown glass for spectacles.
Practice Questions
View allWhich one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
Show answer
Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
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Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
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Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →A lemon kept in water in a glass tumbler appears to be larger than its actual size. It is because of
- A.reflection of light
- B.scattering of light
- C.refraction of light
- D.polarization of light
Show answer
The lemon looks bigger because light from it bends as it passes from water through the curved glass into air.
Read the full explanation →Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?
- A.Most of the space in the atom is empty.
- B.The radius of the atom is about 10⁵ times the radius of the nucleus.
- C.Electrons move in a circular path of fixed energy called orbits.
- D.Nearly all the mass of the atom resides in the nucleus.
Show answer
. Orbits of fixed energy were proposed by Niels Bohr in 1913; Rutherford's experiment said nothing about the energy of electrons.
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