1 Heat and Gases Chapter 4 Transfer Processes

Practice 4.2 (p.118) (b) The down feathers in the jacket trap the
1 A cool air. Air is a poor conductor of heat
2 (a) and reduces heat gain by conduction.
Moreover, the down feathers divide the
trapped air into small packets. This
minimizes the convection of air and
reduces heat gain. Therefore, John will
feel less hot shortly after he goes outside
(b) with a down jacket.
8 (a) When air around the candle is heated, it
expands and rises. The cooler air from
the surroundings moves in to replace the
hot air, forming a convection current as
shown.
(b) In solid, the particles can only vibrate
about a fixed position. It is not possible
3 In convection, particles of a fluid carry energy for the particles to form a current.
from the hot region to the cold region and the
particles in the cold region move along the
convection current to the hot region to absorb
energy. Since no particles exist in a vacuum,
convection does not occur.
4 As the effect of gravity in space is negligible,
warm air does not always rise and cold air
does not always sink. Convection does not
take place.
5 The warm air around the light bulb rises. The
opening lets the warm air flow out. If the
opening is covered, the lampshade may
become overheated.
6 The steam of herbal tea rises. Glass plates can
reduce the energy loss due to evaporation and
convection.
Cold air from freezers sinks and the food in
freezers can be kept frozen even if they do not
have covers.
7 (a) Wear a jacket

New Senior Secondary Physics at Work (Second Edition) 1