CBSE Class 7 Science Heat VBQs

Choose The Correct Answer.

Question. One litre of water at 30ºC is mixed with one litre of water at 50ºC. Then temperature of mixture will be:
a) 80ºC
b) More than 50ºC but less than 80ºC
c) 20ºC
d) Between 30ºC and 50ºC
Answer : D

Question. Which is bad conductor of heat:
a) Aluminium
b) Iron
c) Copper
d) Wood
Answer : D

Question. Land breeze is:
a) Cool air from land to sea
b) Cool air from sea to land
c) Hot air from land to sea
d) Hot air from sea to land
Answer : A

Question. A wooden spoon is dipped in a cup of ice-cream. Its other end:
a) becomes cold by the process of conduction
b) becomes cold by the process of convection
c) becomes cold by the process of radiation
d) Does not become cold
Answer : D

Question. Temperature of human body is:
a) 100ºC
b) 0ºC
c) 37ºC
d) 98ºC
Answer : C

Fill In The Blanks.

(i). The hotness of an object is measured by its temperature.

(ii). The mode of heat transfer without any medium is called radiation.

(iii). Air is bad conductor of heat.

(iv). The normal temperature of human body is 37ºC.

Write True Or False.

Question. Metals are insulators of heat.
Answer : False

Question. We get heat from the sun by radiation. 
Answer : True

Question. Wool is good conductor of heat.
Answer : False

Question. Sea breeze arises due to conduction.
Answer : False

Question. Range of clinical thermometer is 35ºC to 42ºC.
Answer : True

Match The Following :

Answer : (i) - (b), (ii) - (c), (iii) - (d), (iv) - (a),
 

ACTIVITY- To measure the temperature using clinical thermometer.

Question. The clinical thermometer can measure temperature above 45ºC. (T/F)
Answer : False.

Question. The normal temperature of our body is …………….
Answer : 37ºC.

ACTIVITY- Measurement of temperature of water by using a laboratory thermometer. 

Question. The thermometer should not touch the …………….. of the beaker.
Answer : Bottom or sides.

Question. Thermometer should be held from its bulb. (True/False)
Answer : False.

ACTIVITY-Flow of heat through a metal strip.

Question. The handle of electric iron is good conductor of heat. (True/False)
Answer : False.

Question. The handle of cooking vessels are good conductor of heat. (True/False)
Answer : False.

ACTIVITY- Transfer of heat through liquids and gases.

Question. The liquids are always heated from the bottom. (True/False)
Answer : True.

Question. The ventilators in the rooms are used to expel cold air. (True/False)
Answer : False.

ACTIVITY- Dark colour objects absorb more heat.

Question. Dark coloured clothes absorb less heat. (True/False)
Answer : False.

Question. We wear light coloured clothes in winters. (True/False)
Answer : False.

Short Answer Type Questions.

Question. What is the use of kink in a clinical thermometer?
Answer : Kink prevents the level of mercury to fall down even after it is taken out of mouth.

Question. Why do we wear woolen clothes in winter?
Answer : Wool has air trapped inside; air is bad conductor of heat. So woolen clothes keep us warm in winters.

Question. What is lab thermometer? Write its range.
Answer : Laboratory thermometer is used to measure temperature of objects other than living bodies. Its range is usually from -10ºC to 110ºC.

Question. State the condition which determines the direction of flow of heat.
Answer : Heat always flows from hot body (high temperature) to cold body (low temperature).

Question. Why do we prefer dark clothes in winter and light one in summers?
Answer : Dark coloured clothes are better absorbers of heat than the light coloured clothes. So we prefer dark clothes in winter and light one in summers.

Question. What is clinical thermometer? Write its range.
Answer : Clinical thermometer is used to measure temperature of human body. Its range is from 35ºC to 42ºC.

Long Answer Type Questions.

Question. Explain the formation of sea breeze and land breeze in coastal areas.
Answer : During day time land gets heated due to sunlight. The air over the land gets heated, expands and rises upwards. The cooler air from the sea rushes towards the coast to take its place due to convection. This moving air is known as sea breeze.
During the night time, exactly the reverse happens. Due to its higher absorption capacity, the water cools down more slowly than the land, so cool air from the land move towards the sea, this moving air is known as land breeze.

Question. What are various modes of heat transfer? Explain.
Answer : (1) Conduction- The process by which heat is transferred from hotter end to the colder end of a sold body without actual movement of particles is known as conduction.
(2) Convection- The process of heat transfer due to actual movement of heated particles is called convection. Liquids and gases get heated by convection.
(3) Radiation- The process of heat transfer which does not require any medium is known as radiation.
Heat of the sun reaches earth by radiation.