Understanding Light Waves and Visible Light

• Light is an external factor that affects the eye, causing the sense of vision.

Nature of Light Waves

• Light waves are electromagnetic transverse waves.
• They are electromagnetic because they can travel through a vacuum.
• They are transverse because medium particles vibrate perpendicular to the direction of wave propagation, forming crests and troughs.
• The speed of light waves through a vacuum (free space) = 300,000 km/sec or 3 x 10^8 m/sec.

Speed of Light

• The speed of light is the distance covered by light in one second.

Visible Light

• Visible light is a component of the electromagnetic spectrum.
• Visible light has wavelengths ranging between 380-700 nanometers.

Analysis of White Light

• White light splits into seven spectrum colors.

Light Deviation and Wavelength

• The color with the lowest deviation is closest to the prism apex, has the lowest frequency, and the longest wavelength (red).
• The color exhibiting the highest deviation is closest to the prism base, has the highest frequency, and the shortest wavelength (violet).

Energy of Light Waves

• Max Planck discovered in 1900 that the energy of light waves consists of energy quanta called Photons.
• Photon energy (E) is directly proportional to the frequency (F) of the light wave.
• Expressed as: Photon energy = Constant x Photon frequency.
• The constant is known as Planck's constant.
• Therefore, Photon energy = Planck's constant x Photon frequency

Light Behavior Through Different Media

• Light transmits through different media with variable degrees.
• Media can be classified by their ability to allow light to pass through: transparent, translucent (semi-transparent), and opaque.

Transparent Medium

• Transparent medium permits most light to pass through it.
• Objects can be seen clearly through the medium.
• Examples: clear glass and pure water.

Translucent Medium

• Translucent medium permits only a part of light to pass through and absorbs the remainder.
• Objects are seen less clearly.
• Examples: frosted glass and tissue paper.

Opaque Medium

• Opaque medium doesn't permit light to pass through at all.
• Objects cannot be seen through it.
• Examples: plant leaves, books, foil paper, milk, carton, black honey, wood, metals, and human skin.

Light Travels in Straight Lines

• Light travels (propagates) through transparent media in straight lines with a controllable thickness.
• Example: Clothes pins can be seen clearly in a transparent plastic bag because both air and the bag are transparent, allowing light to pass through.
• Example: Impurities are not seen in black honey because it is an opaque medium that doesn't permit light to pass through it.
• Example: A tree leaf is not visible when placed on a book because the leaf is an opaque medium.
• Example: Although water is transparent, fish at the bottom of the River Nile are not visible because the thickness of the water prevents light from passing through.

Light Intensity (Brightness)

• Light Intensity illustrates the degree of the light of a surface by varying the distance between the surface and the light source.
• Light intensity is the quantity of light perpendicularly falling on a unit area of a surface in one second.
• Light intensity of a surface decreases as the distance between the surface and the light source increases.

Inverse Square Law of Light

• The light intensity of a surface is inversely proportional to the square of the distance between the surface and the source of light.
• Light intensity is proportional to 1/d^2.