Maharashtra Board Class 8 Measurement and Effects of Heat

How is temperature different from heat?
Answer: a) Temperature is the total kinetic energy of atoms, while heat is the average kinetic energy.

 

What is the purpose of a clinical thermometer?
Answer: b) To measure body temperature

 

What is the unit of specific heat in the SI system?
Answer: c) Joule/(kg°C)

 

What does a calorimeter measure?
Answer: b) Heat content

 

Why is the inner vessel of a calorimeter made of copper?
Answer: a) It is a good conductor of heat.

Important Notes

I. Introduction

• Heat as a form of energy flow from high to low temperature objects.
• Temperature indicates the hotness or coldness of an object.
• Ice cream has a lower temperature than tea.

II. Various Effects of Heat

• Heat causes expansion and contraction in objects.
• Changes in the state of matter due to heat.
• SI unit of heat: Joule, CGS unit: calorie (1 cal = 4.18 J).

III. Sources of Heat

1. Sun: Nuclear fusion generates heat.
2. Earth: Geothermal energy from the high-temperature core.
3. Chemical energy: Burning fuels (wood, coal, petrol) produces heat.
4. Electrical Energy: Electricity powers devices generating heat.
5. Atomic energy: Fission of elements like uranium produces heat.
6. Air: Contains a significant amount of heat.

IV. Heat and Temperature

• The difference between heat and temperature.
• Temperature relates to the average kinetic energy of atoms.
• Heat is the total kinetic energy in a substance.
• Kinetic energies equalize when temperatures are equal.

V. Thermometer

• Clinical thermometer measures body temperature.
• Working principle: Expansion of liquid (alcohol) with temperature.
• Digital thermometers measure body heat directly.

VI. Calorimeter

• Measures heat content in an object.
• Inner and outer vessels prevent heat transfer.
• Hot or cold objects reach thermal equilibrium with water in the calorimeter.