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What are transparent materials?

Transparent materials are those substances that allow light to pass through them completely. Because of this, objects on the other side can be seen clearly. These materials do not block light. Examples include glass, clean water, and air.

ScienceClass 6CBSE

What are artificial sources of light?

Artificial sources of light are man-made sources that produce light. These are created by humans to provide illumination, especially during nighttime or in dark places. Examples include electric bulbs, tube lights, candles, and gas lamps. These sources are very useful in daily life for lighting homes, streets, and workplaces.

ScienceClass 6CBSE

What is light?

Light is a form of energy that enables us to see objects around us. It travels in the form of waves and does not require a medium to propagate. Although we often describe it as “invisible energy,” it becomes visible when it reflects off objects and enters our eyes. Without light, our surroundings would appear completely dark, and vision would not be possible.

ScienceClass 6CBSE

Write a short note on the water cycle.

The water cycle is the continuous movement of water on, above, and below the surface of the Earth. It involves several processes such as evaporation, condensation, precipitation, and collection. Water from oceans, rivers, lakes, and plants evaporates due to the heat of the sun and rises into the atmosphere as water vapour. This vapour cools and condenses to form clouds. When the clouds become heavy, water falls back to the Earth as rain, snow, or hail, which is known as precipitation. The water then collects in rivers, lakes, and oceans or seeps into the ground as groundwater. From there, it again evaporates, continuing the cycle.

ScienceClass 6CBSE

Why does the rate of evaporation increase on increasing the temperature?

Evaporation is the process by which a liquid changes into vapour. When the temperature increases, the particles of the liquid gain more kinetic energy. Because of this increased energy, the molecules move faster and are able to overcome the forces holding them together in the liquid state. As a result, more molecules escape from the surface of the liquid into the air as vapour. Therefore, higher temperature increases the rate of evaporation.

ScienceClass 6CBSE

How are rivers and streams formed?

Rivers and streams are formed mainly from rainwater and melting snow. When snow on mountains melts, it turns into water and flows downhill due to gravity. This flowing water forms small channels called streams. Many streams join together to form rivers, which flow across land for long distances. Rivers collect water from rainfall, tributaries, and groundwater along their path. Eventually, most rivers empty into lakes, seas, or oceans.

ScienceClass 6CBSE

Why is water used as a coolant in engines?

Water is used as a coolant in engines because it has a high specific heat capacity, which means it can absorb a large amount of heat without a significant rise in temperature. During the combustion of fuel in an engine, a large amount of heat is produced. Water circulating in the radiator system absorbs this heat and carries it away, preventing the engine from overheating. By cooling the engine, water helps in: Maintaining proper engine temperature Preventing damage to engine parts Increasing engine efficiency and lifespan

ScienceClass 6CBSE

Which process is involved in the removal of salt from sea water?

Ans. The process used to remove salt from seawater is called desalination. This process converts saline water into fresh water suitable for drinking and other uses. One common method of desalination involves evaporation followed by condensation. In this method, seawater is heated so that water evaporates and leaves the salt behind. The water vapour is then cooled and condensed to form pure water. Another modern method is reverse osmosis, which uses special membranes to remove salts and impurities from seawater.

ScienceClass 6CBSE

What is the role of transpiration in plants?

Transpiration is the process by which plants lose water in the form of water vapour from the surface of their leaves through small openings called stomata. Transpiration plays several important roles in plants: It helps in cooling the plant during hot weather. It helps in the transport of water and minerals from roots to other parts of the plant. It maintains the water balance within the plant. Thus, transpiration is essential for the proper growth and functioning of plants.

ScienceClass 6CBSE

Is there any variation in the amount of water present on the earth?

Ans. No, the total amount of water present on Earth remains almost constant. Water continuously circulates between the oceans, atmosphere, land, and living organisms through the water cycle. In this cycle, water evaporates from oceans, lakes, and rivers into the atmosphere, forms clouds through condensation, and returns to the Earth as precipitation in the form of rain, snow, or hail. This continuous circulation maintains the balance of water on Earth.

ScienceClass 6CBSE

How does rainwater harvesting increase the water level of underground water?

Rainwater harvesting is the process of collecting and storing rainwater for future use. In this method, rainwater from rooftops or open areas is directed into storage tanks or allowed to seep into the ground through pits and recharge wells. When rainwater seeps into the soil, it recharges underground water sources and raises the water table. This helps in: Increasing groundwater levels Reducing water scarcity Preventing flooding and soil erosion Conserving water for future use Thus, rainwater harvesting is an important method for sustainable water management.

ScienceClass 6CBSE

Why does ice float on the surface of water?

Ice floats on water because it is less dense than liquid water. When water freezes, its molecules arrange themselves in a fixed crystal structure with spaces between them. This structure occupies more volume and reduces the density of ice. Since substances with lower density float on substances with higher density, ice floats on the surface of water. This property is very important for aquatic life because lakes and ponds freeze only at the surface while water below remains liquid, allowing fish and other organisms to survive.

ScienceClass 6CBSE

Why is water called a universal solvent?

Water is called the universal solvent because it can dissolve a large number of substances compared to most other liquids. Many solids, liquids, and gases dissolve easily in water. For example, salt, sugar, minerals, and gases like oxygen and carbon dioxide dissolve in water. This property of water is very important in nature and in living organisms. It helps in: Transporting nutrients in plants and animals Carrying dissolved minerals in rivers and oceans Supporting many chemical reactions in living cells However, it is not truly universal because some substances such as oil and wax do not dissolve in water.

ScienceClass 6CBSE

How much percentage of salt is present in salt water?

Seawater contains a large amount of dissolved salts, which makes it salty. On average, seawater contains about 3.5% dissolved salts. These salts include sodium chloride (common salt) along with salts of calcium, magnesium, potassium, and sulphates. Because of this high salt content, seawater is not suitable for drinking unless the salt is removed through desalination processes.

ScienceClass 6CBSE

How do wet clothes become dry?

Wet clothes become dry because of the process called evaporation. In this process, the water present in the clothes changes into water vapour and mixes with the air. Heat from the surroundings or sunlight provides energy to the water molecules, allowing them to escape into the air. The rate of evaporation increases when: The temperature is high (sunlight or warm air) The wind is blowing (moving air carries away water vapour) The surface area is large (clothes spread out dry faster) Therefore, wet clothes dry faster on a sunny and windy day.

ScienceClass 6CBSE

What is a fused bulb?

A fused bulb is a bulb that does not glow anymore because its filament is broken. Inside an electric bulb, there is a thin wire called a filament that heats up and produces light when current passes through it. If the filament breaks due to overheating or long use, the circuit inside the bulb is broken, and it stops glowing. Such a bulb is called a fused bulb.

ScienceClass 6CBSE

Name two insulators and two conductors.

Insulators: Plastic Rubber Conductors: Aluminum Copper

ScienceClass 6CBSE

Name some devices in which electric cells are used.

Electric cells are used in many portable devices. Some examples include: Portable radio – Uses cells to operate without direct power supply. Camera – Requires cells or batteries for functioning. Wrist watch – Small button cells are used to run the watch. Torchlight – Uses electric cells to produce light in the absence of electricity.

ScienceClass 6CBSE

What are insulators? Give one example.

Insulators are materials that do not allow electric current to pass through them easily. They have tightly bound electrons that do not move freely. Insulators are used to protect us from electric shocks and to cover electrical wires. Examples: Rubber, plastic, wood, glass.

ScienceClass 6CBSE

Name two devices which work on electricity.

Many devices operate using electricity. Two common examples are: Fan – It converts electrical energy into mechanical energy to produce airflow. Electric bulb – It converts electrical energy into light energy.

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