Hot and Cold Temperature - Class 7

Class 7, Chapter 4- Heat, Lesson- 1

1. Hot and cold temperature Suman Kumar Krishna Integrated B.Sc. B.Ed. (Medical)

2. Heat is form of energy flowing from one body of matter to another spontaneously due to their temperature difference. When a hot object and a cold object come in contact with each other, a type of energy flows from the hot object to the colder one. This energy is called heat energy.

3. Heat is a form of energy which makes the substance hot. In winter, it is our common experience that we feel cold inside the house and if we come out in front of sun rays, then we feel warm. Now, if we know that how do we feel this sensation of warm or cold? Then, what will be our answer? Think . In this lesson, we will try to find out the answer to such kind of question.

4. In our daily routine, we come across a number of objects, out of which some are hot while other objects are cold, e.g. when a frying pan kept on a burning gas stove becomes hot but the handle of the pan is cold. Even among the hot objects, some objects may be hotter than the other. In the same manner, among the cold objects, some objects may be colder than the other. So , if I ask you how you decide the relative hotness or coldness of objects, then your answer will be ’by simply touching the objects’.

5. O ur sense of touch is not enough in telling us whether an object is really hot or cold so, this can be understood by performing a simple activity.

6. The degree of hotness or coldness of the object is known as the temperature of an object . The temperature of an object is an only property that indicates which object is hot and which one is cold. A high temperature of a body indicates that it is very hot whereas a low temperature of the object indicates that it is quite cold, e.g. the temperature of boiling water is quite high, so boiling water appears to be very hot. On the other side, the temperature of melting ice is quite low. So, ice appears to be very cold on touch. Temperature

7. It is measured by using an instrument called thermometer, which has a scale marked on it which is used to read the temperature, e.g. the scale in laboratory thermometer is marked along the length of thermometer’s tube between 0° mark and 100° mark into 100 equal divisions. So , each division is called a degree. The temperature of an object should always be stated with its unit. So , the most common unit for measuring temperature is degree Celsius (°C). Thermometer

8. EFFECT OF HEAT When body is heated various types of physical & chemical change take place. PHYSICAL CHANGES a ) CHANGE IN TEMPERATURE On adding heat to body, its temperature increase. On removal of heat from body, its temperature decrease. b ) CHANGE OF STATE On addition or removal of heat to/from body, there is change in state of body. Ex- change of ice to water on addition of heat etc. c ) THERMAL EXPANSION The phenomenon of expansion of matter on heating is called thermal expansion. CHEMICAL CHANGES On heating reactant , many case chemical changes take place.

9. What would happen if we have only winter season on earth? What would happen if we are not able to differentiate between hot and cold temperatures? What would happen if there is no device to measure the temperature?

10. Choose the Correct Option: Which of the following is odd one out? coffee tea soup ice cream

11. State True or False: The hotness of an object is determined by its temperature. [True/ False]. Temperature is measured by a device called thermometer. [True/ False].

12. So, today we have learnt about ‘ Hot and Cold Temperatures ’ and now let’s summarize today’s class:  What is thermometer?  What are two types temperature?  Explain why human senses are not trustworthy sometimes.  Name two places where we use clinical thermometer?

13. Homework Go to a doctor or your nearest health center. Observe the doctor taking temperature of patients. Enquire: why she dips the thermometer in a liquid before use. why the thermometer is kept under the tongue. whether the body temperature can be measured by keeping the thermometer at some place other than the mouth. whether the temperature of different parts of the body is the same or different. You can add more questions which come to your mind.