NCERT 7th Class (CBSE) Science: Heat and Temperature

Question: What is Radiation?

Answer: Radiation is the process by which heat is transferred without any contact between the heat source and the heated object.

Question: Name the thermometer used for measuring the temperature of the human body.

Answer: The thermometer used for measuring the temperature of the human body is called Clinical Thermometer.

Question: Why stainless steel cooking utensils  are usually provided with copper bottoms?

Answer: The reason for this could be that copper is the best conductor of heat than the stainless steel.

Question: By which of the processes (conduction, convection, radiation)it is not possible to transfer heat? In a vacuum and through the solid material.

Answer: In a Vacuum – Conduction and convection

Through the solid material – Convection and radiations.

Question: Why is ice wrapped in gunny bags?

Answer: Gunny bag have a number of fine pores, filled with air. Air being a bad conductor of heat does not allow the external heat to go in and melt the ice.

Question: Why is tea generally served in china clay cups and plates?

Answer: Because the china clay is bad conductor of heat and checks the heat conduction from the tea to the surroundings and thus keeps the tea hot.

Question: Why does a shiny tea pot stay hotter than a dull brown pot?

Answer: A shiny tea pot stays hotter than dull brown pot because the shiny surface does not radiate heat from it.

Question: Why are the radiators in cars painted black?

Answer: Radiators in cars are painted black because black bodies are better radiators.

Question: The cooking utensils are made of metals like aluminium or copper while their handles are made of wood. Why?

Answer: The cooking utensils are made of metals like aluminium or copper because these metals are good conductors of heat so they help in the transfer of heat.

The handles of cooking utensils are made up of bad conductors such as wood, plastic etc. As the handles are made of bad conductors, do not get heated up while cooking and we can hold them easily.

Question: Room heaters have shiny reflectors. why?

Answer: Room heaters have shiny reflectors as the shiny surface absorbs very little heat. They reflect all the heat which makes the room heaters more effective.

Question: List four effects that heat produces.

Answer: The four effects are:

1. Heat causes increase in temperature.
2. Heat causes change of state.
3. Heat causes chemical changes.
4. Heat causes expansion.