Class 7 Science Chapter 4: Heat - NCERT Solutions

Similarities between laboratory thermometer and clinical thermometer are:

 1. Celsius scale is present in both the thermometers.                                                                                                                                                                       2. Both are made up of glass and consists of ling narrow tube.                                                                                                                                                     3. Both of them have a bulb at one end.                                                                                                                                                                                         4. Both contains mercury in them.                                                                                                                                                                                                   5. Both the thermometers are used to measure the temperature. 

Differences between laboratory thermometer and clinical thermometer are:

1. Clinical thermometer is used to measure the human body temperature whereas the laboratory thermometer is used to measure the temperature in the laboratory.                                                                                                                                                                                                                                        2. Clinical thermometer have temperature range between 35 - 42º C whereas the laboratory thermometer have range from -10º C to 110º C.                              3. Clinical thermometer contains kink which prevents backflow of mercury whereas laboratory thermometer does not contain kink.                                             

Conductors: Conductors are those which allows heat to pass through them easily. All metals are good conductor of heat and electricity also. For example: silver, nickle, copper, iron etc.

Insulators: Insulators are those which do not allows heat to pass through them easily, such materials and substances are known as insulators. Examples: plastic, wood, leather, rubber etc.

(a) Temperature
Temperature: Temperature is a measure of how hot or cold something is, specifically, a measure of the average kinetic energy of the particles in an object, which is a type of energy associated with motion. Temperature is measured in degrees Celsius.

(b) Clinical thermometer
Clinical thermometer: A clinical thermometer cannot be used to measure high temperatures because it has been designed to measure only human body temperature which varies over a short range. If a clinical thermometer is used to measure high temperatures, it will get damaged.

(c) Celsius
Celsius: Celsius, also called centigrade, scale based on 0 0 Celsius for the freezing point of water and 100 0 for the boiling point of water.

(d) Radiation
It is the mode of transfer of heat in which heat is transferred through radiations. Example: sun etc.  

(e) Conduction
Conduction: Those materials which allow heat to pass through them easily are called good conductors of heat. All the metals are good conductors of heat and electricity as well.

(f) Dark colour 

Black colour absorbs all the wavelength of lights which are not reflected back to our eyes. it means black colour shirt or cloth absorbs all the light and convert this light into the form of energy (into the heat). 

(i) Land breeze blows during                                    (d) Night
(ii) Sea breeze blows during                                      (c) Day
(iii) Dark coloured clothes are preferred during          (b) Winter
(iv) Light coloured clothes are preferred during          (a) Summer

1. The higher temperature of the land and the lowest temperature in the ocean, because of the temperature difference land gets heat up by the sun so, these breeze blows during night time. In the day, the sun heats up both the ocean and the land.
2. Blowing od breeze is due to the higher temperature difference between the land and the ocean. wind blows from the higher pressure area to the lower pressure area on the land which causes the sea breeze during the day.
3. We prefer to wear black and dark coloured clothes in winter because they absorbs most of the radiation that are coming from the sun which keeps our body warm during the low temperature.
4. We prefered light coloured clothes during summer because light colours reflect heat which helps our body to keep cool.

Wearing more layer of clothes during winters keeps us warm than wearing one piece of clothing because air gets trapped between them. As we know, air is the insulator of heat, so it keeps us warm and prevents the loss of heat from the body. That is why layer of clothing keeps us warmer.

1. Here, the transfer of heat from the burner to the utensil occurs through radiations.                                                                                                                          2. Transfer of heat from utensil to the water, occurs through the process of conduction.                                                                                                                    3. The mode of transfer of heat through one particle of water to the another through the process of connection.  

Mixing of all the colours (VIBGYOR) makes white colour in the end. So, at the places of hot climate the out walls of the house painted white because it is a light colour which reflects most of the radiations that are coming from the sun.

(d) between 30°C and 50°C

The temperature of the mixture will be between 30°C and 50°C because hot water loses the heat and simultaneously cold water gains heat this keeps the temperature in between 30°C and 50°C.

(b) not flow from iron ball to water or from water to iron ball.

The heat will neither flow from iron ball to water and nor from water to iron ball because they both have the same temperature.

(d) does not become cold.

When the wooden spoon is deeped in the cup of icecream it's other end does not become cold because wood is the insulator of heat. That's why its other end does not become cold.

(c) copper is a better conductor of heat than the stainless steel.

Stainless steel pans usually provided with copper bottoms because copper absorbs more heat as compared to others. As we know that copper is a good conductor of heat and electricity too.