In which of the following, heat loss is primarily not due to convection?
- A.Boiling water
- B.Land and sea breeze
- C.Circulation of air around blast furnace
- D.Heating of glass surface of a bulb due to current in filament
Correct answer
Explanation
The correct answer is D, Heating of glass surface of a bulb due to current in filament. The glass of a glowing bulb is heated mainly by radiation from the white-hot filament, not by convection.
Conduction passes heat through a solid from particle to particle, convection carries heat by the actual movement of a fluid, and radiation sends heat as electromagnetic waves that need no medium. The filament of an incandescent bulb reaches well over 2,000 °C and sits in a vacuum or a little inert gas, so most of its heat reaches the glass as infrared radiation.
A is wrong because in boiling water the hot water at the bottom rises and cooler water sinks, forming convection currents. B is wrong because land and sea breezes are convection on a large scale, set up by unequal heating of land and water. C is wrong because the air around a blast furnace is heated, rises and is replaced by cooler air, again by convection.
Exam tip: conduction needs contact, convection needs a moving fluid, radiation needs no medium; the Sun's heat reaches us by radiation.
Practice Questions
View allWhich one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
Show answer
Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin. Sclerenchyma is the tissue that makes plants hard and stiff.
Read the full explanation →Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by
- A.the Right-Hand Thumb rule and it would be in the downward direction.
- B.the Left-Hand Thumb rule and it would be in the downward direction.
- C.the Right-Hand Thumb rule and it would be in the upward direction.
- D.the Left-Hand Thumb rule and it would be in the upward direction.
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For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.
Read the full explanation →Which one of the following statements is true for sound waves propagating in air?
- A.Sound is an electromagnetic wave and transverse in nature
- B.Sound is a mechanical wave and longitudinal in nature
- C.Sound is a mechanical wave and transverse in nature
- D.Sound is an electromagnetic wave and longitudinal in nature
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Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.
Read the full explanation →Which one of the following is primarily responsible for conduction of current in a metal?
- A.Bound electrons
- B.Free electrons
- C.Both bound and free electrons
- D.Ions
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In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.
Read the full explanation →Which one of the following statements is correct about the magnification of an optical microscope?
- A.Magnification increases with the increase in focal length of eyepiece
- B.Magnification increases with the increase in focal length of objective
- C.Magnification does not depend upon the focal length of eyepiece
- D.Magnification decreases with the increase in focal length of eyepiece
Show answer
A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.
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