Convection as a Mode of Heat Transfer

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Questions and Answers

What is the main difference between natural convection and forced convection?

  • Natural convection is a slower process than forced convection due to different heat capacities.
  • Natural convection is driven by gravity, while forced convection is driven by external forces. (correct)
  • Natural convection occurs only in gases, while forced convection occurs only in liquids.
  • Natural convection involves bulk transport of fluid, while forced convection involves heat transfer within a solid material.

What causes the rising of the hot fluid and the sinking of the cold fluid in a natural convection process?

  • The increase in density of the hot fluid.
  • The expansion of the hot fluid due to heating. (correct)
  • The contraction of the hot fluid due to cooling.
  • The decrease in density of the cold fluid.

How does forced convection differ from natural convection in terms of motion?

  • Forced convection happens only in liquids, while natural convection happens only in gases.
  • In forced convection, the fluid is moved by external means, while in natural convection, the fluid moves on its own. (correct)
  • Forced convection is driven by gravity, while natural convection is driven by pumps.
  • In natural convection, the fluid moves laterally, while in forced convection, it moves vertically.

What is the role of gravity in natural convection?

<p>To facilitate the movement of fluids due to their different densities. (A)</p> Signup and view all the answers

Which statement about forced-air heating systems is true based on the text?

<p>Forced-air heating systems move air through a pump mechanism. (A)</p> Signup and view all the answers

Why does the ground heat up more quickly than large bodies of water during the day?

<p>Water has a higher specific heat and disperses absorbed heat due to mixing currents. (C)</p> Signup and view all the answers

What causes the creation of a sea breeze near a large body of water?

<p>Air currents rising (D)</p> Signup and view all the answers

Why does the ground lose heat more quickly at night compared to the water surface?

<p>The water surface is warmer than the land (A)</p> Signup and view all the answers

What effect does the rotation of the earth have on the convection current near the equator?

<p>Modifies the convection current (B)</p> Signup and view all the answers

In the absence of any other factor, what would happen to air near the equatorial surface according to the text?

<p>It would rise and move towards the poles (D)</p> Signup and view all the answers

Why does air descend at 30° N latitude instead of at the poles in the trade wind system?

<p>Effect of the earth's rotation (D)</p> Signup and view all the answers

What is responsible for creating an eastward speed of 1600 km/h close to the equator?

<p>Effect of the earth's rotation (A)</p> Signup and view all the answers

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Study Notes

Convection Types

  • Natural convection occurs due to density differences caused by temperature variations, resulting in the rising of hot fluid and sinking of cold fluid.
  • Forced convection involves an external driving force, such as a fan or pump, to enhance fluid motion.

Natural Convection

  • Gravity plays a crucial role in natural convection, as it pulls the denser, colder fluid downwards, while the warmer, less dense fluid rises.
  • The rising of hot fluid and sinking of cold fluid in natural convection is caused by density differences due to temperature variations.

Forced Convection

  • Forced convection differs from natural convection in that it involves an external driving force, leading to a more uniform and controlled fluid motion.

Heating and Cooling

  • The ground heats up more quickly than large bodies of water during the day due to its lower specific heat capacity.
  • The ground loses heat more quickly at night compared to the water surface due to its lower specific heat capacity.

Atmospheric Phenomena

  • A sea breeze forms near a large body of water due to the temperature difference between the warm land and cool sea surface, causing air to rise over the land and sink over the sea.
  • The rotation of the Earth has a significant effect on the convection current near the equator, causing air to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • In the absence of other factors, air near the equatorial surface would move from the equator towards the poles.
  • Air descends at 30° N latitude instead of at the poles in the trade wind system due to the Coriolis force and the Earth's rotation.
  • The rotation of the Earth is responsible for creating an eastward speed of 1600 km/h close to the equator.

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