Are Various Energy Forms Interconvertible? – Long Answer Questions

Medium Level (Application & Explanation)

Answer:

Energy can change from one form to another. This is called energy conversion.
In a light bulb, electrical energy changes to light and heat.
In a fan, electrical energy changes to mechanical energy (motion of blades).
In a car engine, chemical energy of fuel changes to heat and then to mechanical energy (movement).
In a toaster, electrical energy changes to heat for cooking.
These examples show that energy is interconvertible, but not fully useful due to losses as heat or sound.

Answer:

The law of conservation of energy says energy cannot be created or destroyed.
It only changes from one form to another.
A stone at height has Potential Energy (PE).
As it falls, PE changes into Kinetic Energy (KE).
Near the ground, PE decreases and KE increases.
The total energy, PE + KE, stays constant, if we ignore air resistance.

Answer:

The Sun provides solar energy to the Earth.
This energy heats water in seas and lakes. Water changes to vapor. This is evaporation.
Water vapor rises and cools. It changes back to tiny droplets. This is condensation.
Clouds form and later give rain or snow. This is precipitation.
During condensation, hidden heat (latent heat) is released.
Thus, solar energy becomes heat, then potential energy in clouds and water, and keeps the cycle running.

Answer:

Green plants use photosynthesis.
They take sunlight, carbon dioxide, and water to make glucose (food).
Here, solar energy changes into chemical energy stored in food.
This energy moves to animals when they eat plants.
So plants are the primary source of energy for most life.
Without this conversion, food chains and life would not survive.

Answer:

The Sun heats the Earth unevenly.
Warm air becomes light and rises. Cool air is heavier and moves to fill the space.
This movement of air is called wind.
Here, solar energy becomes thermal energy in air.
Thermal differences create pressure differences.
Pressure differences cause kinetic energy of moving air, which we feel as wind.

Answer:

Take g = 10 m/s² for easy math.
At the top: PE = mgh = 2 × 10 × 5 = 100 J. KE = 0 J.
As it falls: PE decreases; KE increases.
Just before hitting the ground (ideal case): KE ≈ 100 J, PE ≈ 0 J.
With air resistance, some energy goes to heat and sound.
Then KE at the bottom is less than 100 J, but total energy is still conserved in all forms.

Answer:

Given: mass flow per second = 1000 kg/s, g = 10 m/s², height = 10 m.
Theoretical power = m × g × h per second = 1000 × 10 × 10 = 100,000 W (100 kW).
With 80% efficiency, useful electrical power = 0.8 × 100 kW = 80 kW.
The remaining 20 kW is lost as heat, turbine friction, and generator losses.
Some energy also goes into sound and water turbulence.
So energy is conserved, but not all becomes useful electricity.

Answer:

In both, electrical energy changes to light and heat.
A filament bulb converts a large part into heat, not light.
An LED converts more of electricity into light. So it is more efficient.
60 W means it uses 60 joules per second. 5 W uses 5 joules per second.
For similar light, the LED wastes less energy as heat.
Thus, same output, but lower input. This saves power and money.

Answer:

Take g = 10 m/s². Ignore rotation and air for now.
From height 20 m, PE = mgh = m × 10 × 20 = 200m J.
Without friction, all PE becomes KE. So 1/2 m v² = 200m → v = 20 m/s.
If 20% energy is lost to heat and sound, KE = 0.8 × 200m = 160m J.
Then 1/2 m v² = 160m → v ≈ 17.9 m/s.
The drop in speed shows energy loss to surroundings, though total energy is still conserved.

Answer:

In a flashlight, chemical energy in the battery becomes electrical energy.
The current then becomes light energy, and some heat in the bulb or LED.
In cold, battery chemicals react more slowly.
The battery gives less current and lower voltage.
So the flashlight becomes dim or may flicker.
Energy conversions continue, but the rate drops due to temperature effects on the battery.