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ICSE Class 8 Physics Question 2 of 23

Light Energy — Question 3

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Question 3

The diagram given below shows a ray of light AO falling on a surface separating two media. Draw the refracted ray in each, case.

(a)

Ray of light AO falling on a surface separating two media. Draw the refracted ray. Light Energy, Concise Physics Solutions ICSE Class 8.

(b)

Ray of light AO falling on a surface separating two media. Draw the refracted ray. Light Energy, Concise Physics Solutions ICSE Class 8.

(c)

Ray of light AO falling on a surface separating two media. Draw the refracted ray. Light Energy, Concise Physics Solutions ICSE Class 8.
Answer

(a) When light ray AO passes from air (rarer medium) to water (denser medium), it bends towards the normal as shown below.

Completed diagram, light ray AO passes from air (rarer medium) to water (denser medium). Light Energy, Concise Physics Solutions ICSE Class 8.

(b) When light ray AO travels from water (denser medium) to air (rarer medium), it bends away from the normal as shown in the diagram below.

Completed diagram, light ray AO travels from water (denser medium) to air (rarer medium). Light Energy, Concise Physics Solutions ICSE Class 8.

(c) When light ray AO is incident normally to the surface, it passes undeviated as shown in the figure below.

Completed diagram, Light ray AO incident normally to the surface. Light Energy, Concise Physics Solutions ICSE Class 8.

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
EnergyCapacity to do work. SI unit: joule (J)
Kinetic EnergyEnergy of a moving object
Potential EnergyEnergy stored due to position or configuration
Conservation of EnergyEnergy cannot be created or destroyed, only transformed
Renewable SourceEnergy source replenished naturally: solar, wind, hydro, biomass
Non-Renewable SourceExhaustible source: coal, petroleum, natural gas, nuclear fuels
Energy TransformationConversion 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

  1. Define the main concept of this chapter in one sentence.
  2. List the key types or categories discussed in this chapter.
  3. Give three real-life examples related to the main concept.
  4. Draw and label the key diagram of this chapter from memory.
  5. State the main law or principle covered in this chapter.