Important Chapters from NCERT Class 7 Science and Summaries | Science & Technology for UPSC CSE PDF Download

Introduction 

Choosing what to wear depends on the weather. In winter, we wear woolen clothes to stay warm, and in summer, we wear light-colored cotton clothes to stay cool. Understanding temperature and how heat moves helps us pick the right clothes for comfort.

What is Temperature?

Temperature tells us how hot or cold something is when we touch it.

• Celsius Scale: Created by Anders Celsius, this scale sets the freezing point of water at 0°C and boiling point at 100°C.
• Fahrenheit Scale: Created by Gabriel Fahrenheit, this scale sets the freezing point of water at 32°F and the boiling point at 212°F.

Different Thermometers

• How to Use Safely: Clean with antiseptic before and after use, handle with care, and make sure to read the temperature level correctly.

• How to Use Safely: Keep it straight, make sure the thermometer is surrounded by what you’re measuring, and avoid tilting.

Converting Celsius and Fahrenheit

• The relationship between Celsius and Fahrenheit can be calculated using the formula: $\frac{C}{5}=\frac{F}{-}\backslash frac\{C\}\{5\}\; =\; \backslash frac\{F\; -\; 32\}\{9\}$/9

How Heat Moves 

Heat moves to make things the same temperature around them. There are three ways heat can move:

1. Conduction: When heat moves through something solid, like from a hot stove to a pot.
2. Convection: When heat moves through liquids or gases, like warm air rising and cool air sinking.
3. Radiation: When heat moves through empty space, like sunlight warming the Earth.

What to Wear in Different Seasons

• Material: Cotton is great because it lets air move through it and absorbs sweat.
• Color: Light colors help reflect heat away from the body.
• Fit: Loose clothes are better because they let more air flow around your body.

• Material: Wool is perfect for cold weather because it keeps you warm by trapping air in its fibers.
• Features: Wool can soak up moisture without feeling wet, which keeps you warm.
• Types of Clothes: Sweaters, mufflers, and cardigans made of wool help keep the cold out.

Conclusion 

Chapter 6 :Physical and Chemical Changes

Introduction 

Every day, we see many changes happening around us, involving substances transforming in various ways. These transformations can be classified into two main types: physical changes and chemical changes.

Physical Changes

• Definition: A physical change affects only the physical properties of a substance, such as shape, size, color, and state, without forming any new substance.
• Characteristics:
  • Temporary and generally reversible.
  • Does not result in a new substance.
  • Energy forms like heat, light, or electricity are neither absorbed nor released.
• Examples: Heating water, melting butter, cutting paper.

Chemical Changes

• Definition: A chemical change, or chemical reaction, occurs when substances react to form a new substance with different properties.
• Characteristics:
  • Permanent and generally irreversible.
  • Results in the formation of one or more new substances.
  • May involve the emission or absorption of energy.
• Examples: Rusting of iron, burning of magnesium, reaction between vinegar and baking soda.

Examples of Chemical Changes

1. Burning of Magnesium:

   • When magnesium burns, it reacts with oxygen to form magnesium oxide, a white powdery ash.
   • Mixing magnesium oxide with water results in magnesium hydroxide, another new substance.

2. Reaction Between Copper Sulphate and Iron:

   • Iron reacts with a blue solution of copper sulphate to form green iron sulphate and a brown deposit of copper.

3. Vinegar and Baking Soda:

   • Mixing these two substances releases carbon dioxide gas, which turns lime water milky, indicating the formation of calcium carbonate.

4. Rusting of Iron:

   • Iron reacts with oxygen and water to form rust (iron oxide).
   • Preventing rust can be done by oiling, painting, galvanizing, or making stainless steel.

Crystallization

• Process: A physical change where pure crystals are formed from a solution.
• Application: Used to obtain large, pure crystals from impure substances by cooling a hot, concentrated solution.

Preventing Rusting

• Oiling and Greasing: Prevents contact between iron and moist air.
• Painting and Coating: Coating iron with paint or other metals like zinc (galvanizing) blocks moisture contact.
• Converting to Stainless Steel: Mixing iron with elements like chromium and nickel enhances resistance to rust.

Conclusion 

Understanding physical and chemical changes helps us recognize and manipulate the transformations substances undergo in our environment. By learning how these changes occur, we can better manage materials and reactions in everyday life, from preventing rust to performing safe chemical experiments.