Test: Heat And Energy - Class 9 MCQ

Ice floats on water because it expands and becomes less dense than liquid water at 0°C, making it crucial for aquatic life as it provides insulation in cold climates.

Water exhibits anomalous expansion between 0°C to 4°C by contracting when heated from 0°C to 4°C, which is unusual compared to most substances that expand when heated.

The anomalous expansion of water ensures that ice forms on the surface of lakes, insulating the water below and allowing aquatic life to survive in winter, as the denser water remains at the bottom.

The sun is the primary energy source for ecosystems, driving photosynthesis in plants and subsequently supporting various food chains. This solar energy is essential for sustaining life on Earth.

Global warming occurs primarily due to increased concentrations of greenhouse gases like carbon dioxide and methane, which trap heat in the atmosphere and raise Earth's average temperature.

The SI unit of heat is the joule (J), which quantifies energy transfer, while temperature is measured in Kelvin (K) or degrees Celsius (°C).

Heat refers to the energy that flows from a hotter body to a colder one, while temperature quantifies how hot or cold a body is. These concepts are distinct; temperature does not measure energy directly but rather the average kinetic energy of the particles in a substance.

Wind energy systems require steady winds (generally above 15 km/h) to operate efficiently, which can limit their effectiveness in certain regions and conditions.

Water reaches its maximum density at 4°C. This unique property is crucial for aquatic life, as it allows water to sink and create a stable environment for organisms below the ice during winter.

Nuclear energy is produced through the fission of uranium nuclei, releasing a large amount of energy. This process is harnessed in nuclear power plants to generate electricity.

Wind energy is derived from the kinetic energy of moving air, which can be harnessed using wind turbines to generate electricity, showcasing a clean and renewable energy source.

The greenhouse effect refers to the warming of Earth’s surface due to the absorption of long-wavelength infrared radiation by greenhouse gases, which helps maintain a stable climate conducive to life.

Gases indeed expand more than liquids when heated due to their increased molecular motion and lack of fixed shape. This behavior leads to different expansion rates across states of matter, with solids expanding the least, followed by liquids, and then gases.

Energy degradation refers to the phenomenon where energy transformations result in some energy becoming unusable, typically in the form of heat, which reduces overall efficiency in any system.

In Hope's experiment, the bottom thermometer (T2) reached a steady temperature of 4°C before the top thermometer (T1) began to change, demonstrating the unique thermal properties of water.

When two bodies at different temperatures come into contact, energy transfers from the hotter body to the cooler one until thermal equilibrium is achieved. This process is fundamental to understanding heat transfer in thermodynamics.

Solar energy is a renewable energy source because it is abundant and can be harnessed continuously without depleting natural reserves, unlike fossil fuels which are finite and exhaustible.

The first law of thermodynamics is known as the Law of Energy Conservation, stating that energy cannot be created or destroyed, only transformed from one form to another.

Renewable energy sources can be replenished naturally, making them sustainable over time. Examples include solar, wind, and hydro energy, which do not deplete the Earth's resources.

Energy decreases at each trophic level due to energy loss in metabolic processes, heat, and waste, illustrating the inefficiency of energy transfer in ecosystems.