Light

• Visible light is responsible for human sight and is divided into seven colors based on their wavelengths.
• Light is an energy that enables us to see
• The Sun is the most important source of natural light
• Without sunlight, it is impossible for living things to survive on earth
• Light travels at a very high speed
• During a storm, lightning and thunder occur at the same location, but we see lightning first before we hear thunder
• This shows that light travels faster than sound
• Light has the fastest speed in the Universe, traveling at 300,000,000 metres per second in space
• Light travels in straight lines
• Light does not bend but travels in straight lines, referred to as rectilinear propagation
• Light ray


  The straight path of a light source from one point to another
• Beam of light


  A bundle of light rays
• Types of beams of light

  • Parallel beams
  • Divergent beams
  • Convergent beams
• Objects classification


  • Luminous objects
  • Non-luminous objects
• Transparent materials


  • Let most of the light pass through them
  • Appear clear or see-through
  • Objects on the other side can be clearly seen
• Transparent materials


  • Clear glass windowpane, cling wrap, cellophane, water, clear air
• Translucent materials


  • Absorb some light but allow some to pass through
  • Do not show distinct images on the other side
  • Only fuzzy, unclear images are seen through them
• Translucent materials


  • Frosted glass windowpane, wax paper, tinted car windows, sunglasses
• Opaque materials


  • Absorb all light and none passes through
  • Incapable of allowing light to pass through
  • Opposite to transparent and translucent materials
• Opaque materials


  • Wooden door, stone wall, metal roof, closed textbook, human beings
• Shadows formation


  1. Light is blocked by an opaque object, creating an area of darkness called a shadow

  2. Shape and size of shadow depend on the position and size of the light source compared to the object
• Types of shadows


  • Umbra
  • Penumbra
• Umbra


  • The darkest part of a shadow, receives no light at all
• Penumbra


  • Area of a partial shadow that is lighter due to some light from the source
• Point light source


  Creates a single area of shadow called an umbra, uniformly dark with sharp, well-defined edges
• Large or extended light source

  Creates two areas of shadow, an umbra surrounded by a lighter penumbra region with blurry and poorly defined edges
• Eclipse


  When one astronomical body blocks light from or to another
• Sun


  An extended light source in space
• Solar eclipse


  Moon passes between Earth and the Sun and stops some or all of the Sun’s light from reaching Earth
• Types of solar eclipses

  • Partial solar eclipse
  • Total solar eclipse
  • Annular solar eclipse
• Partial solar eclipse


  • The Sun is partly covered when the Moon passes in front of it
• Total solar eclipse


  • The Moon completely covers the Sun
• Annular solar eclipse


  • The Moon does not completely cover the Sun but leaves the edge of the Sun showing. This happens when the Moon is farthest in its orbit from Earth and Earth is closest in its orbit to the Sun
• Where a person is during a solar eclipse

  Determines what is seen: Those in the umbra see the sun appearing dark, those in the penumbra see part of the sun or nothing at all
• Persons in the umbra during a solar eclipse


  Will see a total eclipse
• Persons in the penumbra during a solar eclipse


  Will see a partial eclipse
• Persons out of the umbra and penumbra during a solar eclipse


  Will not see the eclipse
• Lunar eclipse


  Moon moves into the shadow of Earth cast by the Sun
• During a lunar eclipse

  When the Moon passes through the penumbra, it dims slightly in a penumbral eclipse. When it passes through the umbra, the lunar eclipse is partial if the Moon is partly within the umbra or total if the Moon is completely within it
• Reflection


  Occurs when light rays hit a surface and bounce off traveling in a different direction