7th Standard, Science Chapter 3
HEAT
Exercises
- State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer: The similarities and differences between the laboratory thermometer and the clinical thermometer are as follows.
Similarities: (i) Both thermometer used for measure temperature.
(ii ) Both thermometer contain mercury.
(iii ) Both are made up of glass.
(iv) Both have bulb at one end.
Differences:
a) Clinical thermometer is used to measure the temperature of human body and laboratory thermometer is used to measure temperature of different objects in factories and other purpose.
b) The temperature range of Clinical thermometer is from 35°C to 42°C and the temperature range of laboratory thermometer is from 10°C to 110°C - Give two examples each of conductors and insulators of heat.
Answer: The two examples each of conductors and insulators of heat is as follows.
The Conductors: copper, aluminium and iron.
The Insulators: wood and plastic. - Fill in the blanks:
(a) The hotness of an object is determined by its Temperature.
(b) Temperature of boiling water cannot be measured by a clinical thermometer.
(c) Temperature is measured in degree Celsius.
(d) No medium is required for transfer of heat by the process of Radiation.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.
(f ) Clothes of dark colours absorb more heat better than clothes of light colours. - Match the following:
(i) Land breeze blows during (a) summer
(ii) Sea breeze blows during (b) winter
(iii) Dark coloured clothes are preferred during (c) day
(iv) Light coloured clothes are preferred during (d) night
Answer:
(i) Land breeze blows during Night
(ii) Sea breeze blows during Day
(iii) Dark coloured clothes are preferred during winter
(iv) Light coloured clothes are preferred during summer - Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer: When we wear multiple layers, the air trapped between the layers is warmed by your body heat. This warm air acts as a barrier, slowing down the transfer of heat from your body to the colder surroundings. Each layer of clothing creates a new pocket of air, adding to the insulation. A single thick layer doesn’t create as many air pockets and therefore doesn’t provide the same level of insulation. Layering allows you to adjust your clothing based on your activity level and the temperature. You can remove a layer if you get too warm or add one if you get cold. Air is a poor conductor of heat, so multiple layers create multiple air pockets that slow down heat transfer to the cold environment. - Diagram and mark where the heat is being transferred by conduction, by convection and by radiation.
Answer: - In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer: In places of hot climate it is advised that the outer walls of houses be painted white, because in hot climates, white paint on exterior walls helps to keep buildings cooler by reflecting a large portion of the sun’s radiant heat. This reduces the amount of heat absorbed by the building, leading to lower interior temperatures and potentially reduced reliance on air conditioning. - One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be
(a) 80°C (b) more than 50°C but less than 80°C
(c) 20°C (d) between 30°C and 50°C
Answer: (d) between 30°C and 50°C - An iron ball at 40°C is dropped in a mug containing water at 40°C.
The heat will
(a) flow from iron ball to water.
(b) not flow from iron ball to water or from water to iron ball.
(c) flow from water to iron ball.
(d) increase the temperature of both.
Answer: (b) not flow from iron ball to water or from water to iron ball. - 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) does not become cold. - Stainless steel pans are usually provided with copper bottoms. The reason for this could be that
(a) copper bottom makes the pan more durable.
(b) such pans appear colourful.
(c) copper is a better conductor of heat than the stainless steel.
(d) copper is easier to clean than the stainless steel.
Answer: (c) copper is a better conductor of heat than the stainless steel.
Additional Questions and Answers. - What is clinical thermometer?
Answer: The thermometer that measures our body temperature is called a clinical thermometer. - What are the precautions to be observed while using a clinical thermometer?
Answer: Precautions to be observed while using a clinical thermometer are as follows.
( i) Thermometer should be washed before and after use, preferably with an antiseptic solution.
(ii ) Ensure that before use the mercury level is below 35°C.
(iii ) Read the thermometer keeping the level of mercury along the line of sight.
(iv ) Handle the thermometer with care. If it hits against some hard object, it can break.
(v ) Don’t hold the thermometer by the bulb while reading it. - Is the body temperature of every person 37°C?
Answer: The temperature of every person may not be 37°C. It could be slightly higher or slightly lower. - What is the laboratory thermometer?
Answer: A laboratory thermometer is a scientific instrument used to measure the temperature of various substances in a laboratory setting and other things, typically ranging from -10°C to 110°C. - How does heat flow through metal rod? Explain with diagram.
Answer: Take a rod or flat strip of a metal, say of aluminium or iron. Fix a few small wax pieces on the rod. These pieces should be at nearly equal distances (See the picture). Clamp the rod to a stand. If you do not find a stand, you can put one end of the rod in between bricks. Now, heat the other end of the rod and observe. Heat is transferred from the end nearest to the flame to the other end. - What is conduction?
Answer: The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction. - What are Insulators?
Answer: The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators. - What is convection?
Answer: When water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection. - Define Radiation.
Answer: The transfer of heat without any media is called Radiation. From the sun the heat comes to us by another process known as radiation. When we sit in front of a room heater, we get heat by this process. - What are conductors? Give example.
Answer: The materials which allow heat to pass through them easily are conductors of heat. For examples, aluminium, iron and copper. - What is Sea breeze?
Answer: During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up. The cooler air from the sea rushes in towards the land and warm air from the land moves towards the sea. The air from the sea is called the sea breeze. - What is land breeze?
Answer: The water cools down more slowly than the land. So, the cool air from the land moves towards the sea. This is called the land breeze.
