PHYSICS PROJECT (:

Sample Questions


Ans: B.
Copper is a good conductor of heat and conducts the heat away from the flame, causing the flame to be extinguished.


Ans: A.
Heating element is placed at the bottom to set up the convection current in order to heat up the water in electric kettle. With the heating element at bottom, water at the bottom warms up, becomes less dense and rises, and push down the cooler (denser) water to the bottom.


Ans: C.
Both air and glass are poor conductors of heat, this reduces heat flowing through window by conduction. Heat flowing through window by radiation is hard to prevent as radiation does not require any medium, hence heat flow through window mainly by radiation.


Ans: B.
Astronaut in space should wear highly reflective surface so as to not absorb the thermal energy in space and to reflect it away.


Ans: D.
Vacuum is a perfect insulator. Both conduction and convection requires medium and vacuum is not a medium, this prevents heat transfer by conduction and convection. Radiation can transfer heat in vacuum as it does not require a medium. Heat can still be lost through radiation in a thermo flask.


Ans:
a) The cup is expanded which takes a longer time for heat to be transferred into surroundings by conduction. It is also made of polysterine material, which is a poor conductor of heat, hence reduces thermal energy loss. Air trapped in expanded polysterine cannot flow and air is a poor conductor of heat, hence thermal energy loss is reduced. It is also white in colour, which reduces heat loss through radiation.

b) The cover prevents heat loss from surface of drink by convection and evaporation.


Ans:
a) Copper is a metal which contains many free electrons in it. Thermal energy is transferred through molecular vibrations and free electron diffusion. When heated, particles in copper gain kinetic energy and start to vibrate vigorously. Particles start to transfer thermal energy to neighbouring particles through vibrations When heated, the free electrons, which are able to move freely, gain kinetic energy and carry thermal energy in them, diffuse to the cooler part of copper. Electrons move very fast and transfer their thermal energy through collisions with other particles.

b) In air, particles are spread far apart from each other and are able to move about freely, thermal energy transfer is by molecular collisions. Unlike in solids, particles are closely packed together and not able to move about freely, thermal energy transfer is by vibrations. In air, due to the large distance between particles, molecular collisions is less frequent so transfer of thermal energy is slower, hence air is a poor conductor of heat.