Class 7 Exam  >  Class 7 Notes  >  Science Class 7  >  Long Question Answer: Heat

Class 7 Science Chapter 3 Question Answers - Heat

Q1. How to read a clinical thermometer? 
Ans: Reading a Clinical Thermometer
There are following steps to read the temperature on a thermometer.

  • Step I: Firstly, wash the thermometer with an antiseptic solution and if in case, the antiseptic solution is not available, then wash it with a clean water.
  • Step II: Gently, hold the thermometer tube in your hand and give it a jerk in such a way that the mercury thread in the thermometer tube falls below the reading of 35°C.
  • Step III: Now, put the bulb of the thermometer under the tongue of the patient for about one minute. Then take out the thermometer from patient’s mouth.
  • Step IV: In order to read the temperature, hold the thermometer horizontally in your hand and rotate it slowly. When we see a magnified image of the mercury thread in its tube, then a position will come. Now, read the temperature on thermometer tube in level with the top of the mercury thread.

Q2. What precautions should we take to read a clinical thermometer?

Precautions while Reading the Thermometer: A clinical thermometer should not be used for any object other than the human body. There are some following precautions which are to be observed while reading a clinical thermometer.

  • Wash the clinical thermometer before and after using preferably with an antiseptic solution.
  • Be ensure that the mercury level before using the clinical thermometer should be below 35°C.
  • The clinical thermometer should be read by keeping the level of mercury along the line of sight.
  • While reading the clinical thermometer, it should never be held by the bulb.
  • The clinical thermometer should be carefully handled.

Q3. List any four effects of heat. Explain them. 

Ans: When heat energy is absorbed by a body various changes can happen. Some of them are: 

  • Rise in temperature: When a body absorbs heat, it gains energy. As a result of this, temperature of the body rises and body becomes hot. 
  • Change in state of matter: On heating, most of the substances change its state, like solid to liquid, liquid to gas, etc. 
  • Expansion: All state of matter i.e., solid, liquid or gas expand on heating and contract on cooling. Expansion is most in gases, less in liquids and least in solids. Expansion due to heat is known as thermal expansion. 
  • Combustion: On heating, some of the substance reach their ignition temperature and starts burning. So heat causes combustion.

Q4. Instead of water explain the reason, why do the mercury is used in the thermometer?
Ans: Due to following reasons, mercury is used in the thermometers instead of water

  • When the thermometer breaks, the mercury can be easily collected.
  • Mercury can has more expansion than the water.
  • Also, mercury do not stick on the walls of thermometer like water.

Q5. The clinical thermometer is not used to measure high temperature. Why? Also State the limitation of clinical thermometer.

Ans: 

  • Clinical thermometer has the range 35°C to 42°C. If we use it to measure high temperature, it may break and mercury present in the clinical thermometer is harmful. So, we cannot use clinical thermometer to measure high temperature.
  • The clinical thermometer cannot be used for measuring the temperature of any object more than 42°C (i.e. more than the body temperature). If it kept in the sun or near a flame, then this clinical thermometer can be break.

Q6. Differentiate between two modes of transfer of heat, i.e. convection and conduction.
Ans: Difference between convection and conduction
Class 7 Science Chapter 3 Question Answers - Heat


Q7. Observe the picture given in figure. Water is being boiled in a pan of wide base.
Class 7 Science Chapter 3 Question Answers - Heat(a) Which position P or T will feel warmer?
(b) Fill up the boxes P and T to indicate the mode of flow of heat to the hand.

Ans:
(a) As in the given diagram, position P will feel warmer because of heat, air rises.
(b) The flow of heat to P is a convection process and flow of heat to T is radiation.

Q8. Explain the differences between heat and temperature.
Ans: The differences between heat and temperature are given as below
Class 7 Science Chapter 3 Question Answers - Heat


Q9. Prove with the help of an experiment that heat radiation can travel through vacuum.
Ans: First of all, take a flat bottom flask and fix a rubber stopper having two holes in the mouth of the flask. Shift a thermometer through one hole and a glass tube with stopper through the other hole. Now, with the help of a vacuum pump, remove the air from the flask and try to record the temperature from the thermometer. Put a flask in the bright sunlight and we will observe that the thermometer records a rise in temperature. So, on this basis, we can say that this experiment proves that the heat radiation can travel through vacuum.

Q10. Describe in detail about the occurrence of oceanic currents.
Ans: Since, it is a fact that the water present in the ocean (near the equator) is heated by the sun to a very higher temperature than the water near the poles of the earth. It is due to the falling of the sun rays perpendicularly in the equatorial region. So, in the equatorial region, the ocean water expands and becomes lighter.
While on the other side, the water in the polar region remains cold and heavy. It leads to the flow of convection currents of heat of warm water from the equator towards the poles.
Heat of the cold water flow from the poles towards the equator just below the surface of ocean. So, these types of currents are known as oceanic currents.

Q11. Write about clinical thermometer. What is laboratory thermometer?
Ans: 

  • A thermometer specifically designed for the measurement of the temperature of our body is called a clinical thermometer. It consists of a long, narrow glass tube. It has a bulb at one end, which contains mercury. It reads temperature from 35°C to 42°C.
  • The thermometer which is used to measure the temperature of objects in laboratory is called a laboratory thermometer. Its range is -10°C to 110°C.

Q12. What are the differences between temperature and heat?
Ans:
Class 7 Science Chapter 3 Question Answers - Heat


Q13. Write any three precautions to be taken while reading a clinical thermometer.
Ans:

  • Do not hold the thermometer by the bulb.
  • Read the thermometer keeping the level of mercury along the line of sight.
  • Ensure that before use the mercury level is below 35°C.


Q14. Can a clinical thermometer be used to measure the temperature of boiling water?
Ans: No, a clinical thermometer cannot be used to measure the temperature of boiling water because the temperature of boiling water is more than the fixed range of the clinical thermometer, i.e., 42°C. If we try to measure the temperature of boiling water, it will break down.

Q15. Explain how the temperature of water can be measured by using a laboratory thermometer.
Ans: To measure the temperature of water by using a laboratory thermometer, we follow the following steps:

  • Take water in a beaker.
  • Dip the laboratory thermometer in the water so that its bulb gets completely immersed in it, but make sure the bulb doesn’t touch the bottom of the beaker.
  • Hold the thermometer vertically.
  • Consider the movement of the thread of mercury.
  • After it becomes static, notice the reading.


Q16. What is temperature? Describe two types of thermometers used to measure the temperature.
Ans: A reliable measure of the hotness of an object is called its temperature. It is measured by a device called thermometer.
There are two types of thermometer:
(i) Clinical thermometer: The thermometer that measures the temperature of our body is called clinical thermometer. It consists of a long, narrow, uniform glass tube. It has a bulb at one end which contains mercury. Outside the bulb a small shining thread of mercury can be seen. There is also a scale on the thermometer. The scale used in it is the celsius scale, indicated by °C. A clinical thermometer reads temperature from 35°C to 42°C.
Class 7 Science Chapter 3 Question Answers - Heat(ii) Laboratory thermometer: This type of thermometer is used to measure the temperature of different objects in laboratories. It is made of a thin glass tube sealed at one end and a bulb with mercury at the other end. The portion of the capillary tube above the bulb is graduated in degrees usually from -10°C to 110°C.
Class 7 Science Chapter 3 Question Answers - Heat


Q17. What do you mean by transfer of heat? Explain the process of transfer of heat in solids, liquids and gases.
or
What do you mean by transfer of heat? Explain the process of transfer of heat.
Ans: 
Flow of heat from one object to another whether solid or liquid is called transfer of heat. Heat always flows from a body at higher temperature to another body at lower temperature. In other words, heat always flows from a hotter body to a colder. In this process, the temperature of hot body falls as it releases heat which is received by the colder body or a body having lower temperatures. Thus the temperature of the colder body or less hotter body rises. The flow of heat stops when temperature of both the bodies becomes equal.
Transfer of heat take place through conduction, convection and radiation. Conduction is the process of transfer of heat from one particle to the next particle in a solid without the particles actually moving from their position.
Convection is the process of heat transfer in which the particles change their positions by constantly moving from the hotter region to the cooler region, thus causing heat energy to flow. In convection heat travels through the liquids and gases.
Radiation is the process of heat transfer from a hot body to a colder body without any medium between the two.

Q18. Explain the term radiation.
or
Explain how can heat travel in vacuum or without medium.
Ans: The heat from the sun cannot reach us by conduction or convection as there is no medium such as air in most part of the space between the earth and the sun. This is possible through the process of radiation. The mode of transfer of heat energy in which no medium is needed to transfer heat from a hotter body to a colder body is called radiation. It can take place whether a medium is present or not. For example, when we sit in front of a room heater we get heat by this process.
A hot utensil kept away from the flame cools down as it transfers heat to the surroundings by radiation. Our body too, gives heat to the surroundings and receives heat from it by radiation. The figure below show the radiation by the sun. It also shows that when radiation falls on an object a part of it is reflected, a part is absorbed and a part may be transmitted.
Class 7 Science Chapter 3 Question Answers - Heat
Q19. How does the heat travel in air? Explain the sea breeze and land breeze in coastal areas in this reference.
Ans: Heat travels in air through the process of convection. The air near the heat source gets hot and rises up. The cool air from the sides comes in to take its place. In this way the air gets heated up.
Class 7 Science Chapter 3 Question Answers - Heat

In the coastal areas, people experience an interesting phenomenon. The land gets heated faster than the water during the day. The air over the land becomes hotter and rises up. The cooler air from the sea rushes in towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle.
The flow of cool air from the sea towards the land to replace the hot air on land, is called sea breeze. At night it is just the reverse: The water cools down more slowly than land. So the cool air from land moves toward the sea. This is called land breeze.

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