Ques 1: In which direction the transfer of heat normally takes place?
Transfer of heat takes place from an object of high temperature to another object having low temperature. This will happen until the heat equilibrium is created between both the objects.
Ques 2: What is the cause of heat generation in the following cases:-
(a) We apply brakes on our fast-moving car
When we apply brakes then the brakes enable the tyres to stop creating a frictional force between the road and tyres. When they tend to rub against each other at high speed then heat is generated due to excess frictional force between them.
(b) People often jump up and down to feel warm in cold weather
When we jump up and down then we are using our muscular energy. Slowly this muscular energy gets converted into heat energy and we feel warm.
Ques 3: State two types of physical changes when a substance is heated.
When we heat a substance then state changes may occur. Let us take the example of ice. When we start heating ice then it will change into water on heating. When we keep heating the water formed from ice, slowly it will convert into vapours ( gaseous state). so, here two changes have occurred. Solid to liquid and liquid to a gaseous state.
Ques 4: In what way( s) a clinical thermometer differs from an ordinary thermometer?
A clinical thermometer is designed to measure the human body temperature only while an ordinary thermometer can measure the temperature of any object or surrounding. A clinical thermometer can measure only for short range of temperature i.e. ( 35 degree Celsius to 42 degree celsius) whereas an ordinary thermometer measures from -10 degree celsius to 110 degree celsius.
Ques 5: State mode/different modes of heat transfer, in the following situations.
(a) A paper cup, full of hot soup, lying on the table.
Here the mode of heat transfer is Convection mode of heat transfer. The heat gets transferred from a body of high temperature to low temperature
(b) Cooking vegetables in a pan
Heat transfer mode here is conduction as there is a medium.
(c) Melting of chocolate in school bag on a hot summer day.
Here the mode of heat transfer is Radiation as no medium is involved. Radiation does not need any medium for the transfer of heat.
(d) Cooking food in a microwave oven
Here the mode of heat transfer is Radiation. No direct medium is involved in heating.
Ques 6: What is meant by sea breeze? When does it occur?
Sea breeze is a wind that flows from the sea ( water body source) towards the land area nearby. This happens due to the difference in heat between the two surfaces. The land becomes hotter. This occurs during the excessive heat during the daytime. At night, the process get reversed and the land cools up quickly.
(c) A new quilt is warmer than an old one.
Ans (c) The air space between the layers of quilt reduces with time as the cotton gets compressed with time. A new quilt has air spaces between them. The air act as an insulator and does not allow the heat to move out.
(d) A brass tumbler feels much cooler than a wooden tray on a chilly day.
Brass is a good conductor of heat. When someone touches the brass tumbler then the heat gets transferred from the object to the tumbler. The tumbler thus feels cold. Wood is not a good conductor so heat does not get transferred from body to wooden tray.
(e) The bottom of cooking utensils are often kept black
The black colour is a good absorber of heat. So, the bottom of the utensils is painted black so that they absorb a good amount of heat so that food can be cooked fast and easily.
Ques 3: Akshit visited Rishikesh during the summer holidays. There were two tents in the campsite, one was made from a black tent and the other one was made of white fabric. Which one should Akshit prefer? Give reason for the choice. Should Akshit prefer the same tent during winters?
Ans 3: In the summer season he should prefer the white tent as white colour is not an absorber of heat like the black colour. In winter he should choose the black tent because black colour is good absorber of heat. The black tent will be warmer than white tent. So, he should stay in black tent.
Ques 4: Explain how winds are caused?
Ans 4: Winds are caused by the difference in the atmospheric pressure. When a difference between atmospheric pressure occurs then air will travel from an area of high pressure to an area of low pressure.
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