Important points to remember :
- A huge amount of heat is produced in a very short time when the nuclei of some elements like uranium, thorium etc undergo fission. This is used in atomic energy projects.
- Thermometer that is used when someone at home has fever. That thermometer is called clinical thermometer.
- A calorimeter is used to measure the heat content of an object.
- Using this equipment, we can measure the heat produced or absorbed in a physical or chemical process.
Question 1: A. Whom should I Pair with?
Group A Group B
a. Temperature of a
healthy human body 296 K
b. Boiling point of water 98.6∘F
c. Room temperature 0∘C
d. Freezing point of water 212∘F
a. Temperature of a healthy human body – 98.6∘F
b. Boiling point of water – 212∘F
c. Room temperature – 296 K
d. Freezing point of water – 0∘C
B. Who is telling the truth?
a. The temperature of a substance is measured in joules.
Answer : a. Sentence a is lying as heat energy is measured in joules.
b. Heat flows from an object at higher temperature to an object at lower temperature.
Answer : Sentence b is telling the truth as heat energy flows from an object at higher temperature to an object at lower temperature.
c. Joule is the unit of heat
Answer : Sentence c is telling the truth as joule is the unit of heat.
d. Objects contract on heating
Answer : Sentence d is lying as objects expand on heating.
e. Atoms of a solid are free.
Answer : Sentence e is lying as atoms of a solid are closely packed because of force attraction between them.
f. The average kinetic energy of atoms in a hot objects is less than the average kinetic energy of atoms in a cold objects.
Answer : Sentence f is lying as the average kinetic energy of atoms in a hot objects is greater than the average kinetic energy of atoms in a cold objects.
C. You will find if you search.
a. A thermometer is used to measure temperature.
b. The apparatus used to measure heat is called a calorimeter.
c. Temperature is the measures of the average kinetic energy of the atoms in a substance.
d. The heat contained in a substance is the measures of the total kinetic energy of atoms in the substance.
Question 2: Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why?
Answer : Shivani’s tea will be prepared first. In Shivani’s case, the intensity of the flame in contact with the vessel is very high due to which the flow of heat will be faster. Thus, the time taken by the tea to reach its boiling point will be less. Hence, tea will be prepared fast.
In case of Nishigandha, the intensity of radiation reaching the vessel is not as high as compared to stove’s flame. Thus, the flow of heat will be slower in this case due to which more time will be taken to reach the boiling temperature of the tea. Hence, tea will be prepared at slower rate.
Question 3: Write brief answers.
a. Describe a clinical thermometer. How does it differ from the thermometer used in laboratory?
Answer : Clinical thermometer is used to measure body temperature however laboratory thermometer is not used for the purpose of measuring body temperature. The temperature range of clinical thermometers is 35°C-42°C and that of laboratory thermometers is -10°C-110°C. The least count of both the thermometers is different.
b. What is the difference between heat and temperature ? what are their units.
Answer : Heat measures both kinetic and potential energy contained by molecules in an object. On the other hand, temperature measures average kinetic energy of molecules in substance. … The standard unit of measurement of heat is Joules, while that of temperature is Kelvin, but it can also be measured in Celsius and Fahrenheit.
c. Explain the construction of a calorimeter. Draw the necessary figure.
Answer : A calorimeter is a device used to measure the heat flow of a chemical reaction or physical change. The process of measuring this heat is called calorimetry. A basic calorimeter consists of a metal container of water above a combustion chamber, in which a thermometer is used to measure the change in water temperature.
d. Explain why rails have gaps at specific distances.
Answer : These gaps which are of the order of a few millimeters, are provided to allow room for the rails to expand the rise in temperature due to the atmospheric temperature as well as the friction caused by running of train. … So that there is enough margin for the tracks to expand and contract due to the temperature changes.
e. Explain with the help of formulae the expansion coefficients of liquid and gas.
Answer : Coefficient of thermal expansion measures the fractional change in size due to small change in temperature. Metals expand more and have relatively high values of coefficient of linear expansion. The fractional change in volume of a substance due to change in temperature is called coefficient of volume expansion.
# Can you recall
1. Which sources do we get heat from?
Answer : Heat, also known as thermal energy, is a type of energy that can be converted from other types of energy. Thermal energy is necessary to sustain life. Natural sources of heat energy can be found in plant and animal products, fossil fuels, the sun and from within the Earth.
2. How is heat transferred?
Answer : Heat can travel from one place to another in three ways: Conduction, Convection and Radiation. Both conduction and convection require matter to transfer heat.
3. Which effects of heat do you know?
Answer : Symptoms of heat exhaustion may start suddenly, and include:
- Nausea or irritability.
- Muscle cramps or weakness.
- Feeling faint.
- Heavy sweating.
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class 8 science notes state board, when a substance having mass 3kg, the heat contained in a substance is the measure of the kinetic energy of atoms in the substance, difference between heat and temperature