Fill in the blanks:
(a) Work is said to be done by a force only when ............... .
(b) Work done = Force x ............... .
(c) The energy of a body is its capacity to do ............... .
(d) The S.I. unit of energy is ............... .
(e) The potential energy of a body is due to its ............... and kinetic energy of a body is due to its ............... .
(f) Gravitational potential energy U = mass x force of gravity on unit mass x ............... .
(g) Kinetic energy = x mass x ............... .
(h) Power P = ............... / time taken.
(i) The S.I. unit of power is ............... .
(j) 1 H.P. = ............... W.
(a) Work is said to be done by a force only when the body moves.
(b) Work done = Force x distance moved in the direction of force.
(c) The energy of a body is its capacity to do work.
(d) The S.I. unit of energy is joule .
(e) The potential energy of a body is due to its state of rest or position and kinetic energy of a body is due to its state of motion.
(f) Gravitational potential energy U = mass x force of gravity on unit mass x vertical height.
(g) Kinetic energy = x mass x (speed)2.
(h) Power P = Work done by the body / time taken.
(i) The S.I. unit of power is watt (W).
(j) 1 H.P. = 746 W.
Chapter Overview: Energy
Energy is the capacity to do work, measured in joules (J). It exists in various forms: kinetic (motion), potential (position), heat, light, sound, chemical (bonds), electrical (current), and nuclear (atomic nucleus). Energy can be transformed from one form to another — for example, an electric bulb converts electrical energy to light and heat, a solar panel converts light to electrical energy, and our body converts chemical energy (food) to kinetic and heat energy. The law of conservation of energy states that energy cannot be created or destroyed, only transformed; total energy remains constant. Energy sources are classified as renewable (solar, wind, hydro, geothermal, biomass, tidal — replenished naturally, low pollution) and non-renewable (coal, petroleum, natural gas, nuclear fuels — exhaustible, cause pollution). The growing energy crisis requires conservation: using LED bulbs, public transport, solar heaters, energy-efficient appliances, and reducing wastage.
Key Definitions & Concepts
| Term | Definition / Details |
|---|---|
| Energy | Capacity to do work. SI unit: joule (J) |
| Kinetic Energy | Energy of a moving object |
| Potential Energy | Energy stored due to position or configuration |
| Conservation of Energy | Energy cannot be created or destroyed, only transformed |
| Renewable Source | Energy source replenished naturally: solar, wind, hydro, biomass |
| Non-Renewable Source | Exhaustible source: coal, petroleum, natural gas, nuclear fuels |
| Energy Transformation | Conversion of energy from one form to another |
Must-Know Points for Exams
- Energy = capacity to do work. Unit: joule (J).
- 8 forms: kinetic, potential, heat, light, sound, chemical, electrical, nuclear.
- Law of conservation: total energy of an isolated system is constant.
- Renewable sources: inexhaustible, low pollution. Non-renewable: exhaustible, cause pollution.
- Nuclear fuels (uranium) are NON-renewable despite being very powerful.
- Conserve energy: LED bulbs, public transport, solar heaters, switch off when not in use.
Quick Self-Test
- Define the main concept of this chapter in one sentence.
- List the key types or categories discussed in this chapter.
- Give three real-life examples related to the main concept.
- Draw and label the key diagram of this chapter from memory.
- State the main law or principle covered in this chapter.