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A heat source S is placed near a hand held at three different positions, with the dominant mode of heat transfer at the three positions labelled a, b and c. The hand in contact transfers heat one way, the hand held above receives rising hot air, and the hand held to the side receives heat across the gap. Which matching is correct?
- a - conduction; b - convection; c - radiation
- b - conduction; a - convection; c - radiation
- a - conduction; c - convection; b - radiation
- c - conduction; b - radiation; a - convection
Correct answer: a - conduction; b - convection; c - radiation
Solution
The three principal modes of heat transfer are distinguished by their mechanism. Position a (direct contact with the source) transfers heat by conduction. Position b (above the source) is warmed by hot air rising from the source, which is convection. Position c (to the side, across a gap) is warmed mainly by infrared radiation, which needs no medium and travels in all directions.
Related JEE Advanced Physics questions
- Match the temperature of a blackbody listed in Group-I to the corresponding statement in Group-II, and select the correct answer.
[Given: Wien’s constant = 2.9 × 10⁻³ m-K and hc/e = 1.24 × 10⁻⁶ V-m]
Group-I:
(P) 2000 K
(Q) 3000 K
(R) 5000 K
(S) 10000 K
Group-II:
(1) The peak wavelength of emitted radiation can cause photoelectron ejection from a metal with a work function of 4 eV.
(2) The peak wavelength of emitted radiation falls within the visible spectrum.
(3) The peak wavelength of emitted radiation produces the broadest central diffraction maximum in a single-slit setup.
(4) The energy radiated per unit area is one-sixteenth of that emitted by a blackbody at 6000 K.
(5) The peak wavelength of emitted radiation is suitable for imaging human bones.
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- Two rods are connected end to end. Rod 1 has length l and thermal conductivity 2K. Rod 2 has length 2l and thermal conductivity K. Both rods have the same cross-sectional area. What is the effective thermal conductivity of the combination?
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- A continuous-flow calorimeter is used in two separate experiments to find the specific heat of a liquid. In the first trial, supplying 60 W raises the liquid temperature by 10 K. In the second trial, the power is doubled to 120 W, but the same 10 K rise is maintained by tripling the flow rate. Assuming heat loss to surroundings is the same in both trials, what is the power lost to the surroundings?
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