Ray Model of Light

Light Summary Notes

Properties of Light

  • Light travels in straight lines.

  • A light ray:

    • Definition: A thin line of light emitted by a source.

    • Representation: Drawn as a straight line with an arrow indicating direction.

Object Visibility

  • Light rays must enter our eyes for us to see an object.

  • Luminous Objects:

    • Definition: Objects that emit light in all directions (e.g., the Sun, lamps).

    • Function: Light from luminous objects enters our eyes, allowing visibility.

  • Non-Luminous Objects:

    • Definition: Objects that do not emit their own light.

    • Function: Can only be seen when reflecting light from another source (e.g., a lamp).

Reflection

  • Reflection:

    • Definition: The bouncing of light rays off a surface.

  • Plane Mirror:

    • Definition: A mirror with a flat surface.

Characteristics of Images Formed by a Plane Mirror

  1. Object and image are equidistant from the mirror.

  2. Image is upright.

  3. Image is laterally inverted (left becomes right, right becomes left).

  4. Image is virtual (cannot be captured on a screen).

  5. Object and image have the same size.

Mnemonic for Image Characteristics

  • So Do U Like Very Strong Superman Ray

Law of Reflection

  • Angle of incidence (B9) = Angle of reflection (B2)

    • Notation: ( hetai = hetar)

Drawing Ray Diagram for a Plane Mirror (IMPORTANT)

Steps:

  1. Locate Image Position:

    • Distance of object from mirror equals distance of image behind the mirror.

  2. Draw Ray to Eye:

    • Use solid lines with arrowheads for actual light rays reflecting into the eye.

    • Use dotted lines for paths behind the mirror (not actual light rays).

  3. Draw Incident Ray:

    • Lines join the object to the point of incidence on the mirror.

    • Arrowheads on these lines should point towards the mirror.

Types of Mirrors

  • Plane Mirrors: Form upright and undistorted images.

  • Convex Mirrors:

    • Definition: A mirror that curves outward.

    • Also known as diverging mirrors.

    • Application: Blind-corner mirrors for drivers to see around corners.

    • Image Characteristics:

    • Upright, distorted, and smaller images.

  • Concave Mirrors:

    • Definition: A mirror that curves inward.

    • Also known as converging mirrors due to their focusing capability.

    • Image Characteristics:

    • Can form virtual and magnified images.

Types of Reflection

  • Regular Reflection:

    • Occurs on smooth surfaces.

    • Results in clear, undistorted images.

  • Irregular Reflection:

    • Occurs on rough surfaces.

    • Parallel light rays scatter in different directions.

    • No image is formed at the surface.

    • Example: Used in solar cookers that utilize concave mirrors to concentrate rays to heat food.

Refraction

  • Refraction:

    • Definition: The bending of light as it travels from one medium to another of different optical density.

  • Optical Density:

    • Definition: A measure of how fast light can travel through a material.

    • Characteristics:

    • Optically denser materials slow down light relative to air (e.g., water, glass).

    • Light travels faster in air than in water or glass.

  • Behavior of Light in Different Mediums:

    • When light travels from air into glass/water:

    • Slows down and bends towards the normal line.

    • Angle in air (i) is greater than angle in glass/water (r).

    • When light travels from glass/water into air:

    • Speeds up and bends away from the normal line.

    • Angle in air (r) is greater than angle in glass/water (i).

  • Path Example:

    • Light ray enters glass block at point A, bends towards normal upon entry.

    • Light ray exits at point B, bends away from normal.

Apparent Depth

  • Observation: An object underwater appears closer when viewed from outside due to refraction.

  • Example: Light from goggles underwater bends away from the normal while traveling from water to air, affecting our perception of depth.

Dispersion of Light

  • Seven Colors of the Rainbow:

    • Colors: Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).

  • Observation of Dispersion:

    • Dispersion occurs when light passes through a prism.

    • A prism is optically denser than air, causing different colors to bend at various angles.

Electromagnetic Radiation

  • Light as Electromagnetic Radiation:

    • Light is one type of electromagnetic radiation, alongside infrared and ultraviolet radiation.

  • Infrared Radiation (IR):

    • Applications:

    • Thermal imaging to screen for fevers.

    • Used in remote controls.

    • Harmful Effects:

    • Overexposure can cause eye damage.

    • Contributes to climate change when trapped in the atmosphere.

  • Ultraviolet (UV) Radiation:

    • Applications:

    • Stimulates Vitamin D production in the body.

    • Used to sterilize medical equipment, an environmentally friendly method for killing bacteria and viruses.

    • Harmful Effects:

    • Overexposure can harm eyes and increase risk of skin cancer.

  • Visible Light:

    • Applications:

    • Enables visual perception.

    • Essential for photosynthesis in plants to produce sugars from carbon dioxide and water.

    • Harmful Effects:

    • Can cause chemical changes in materials; flash photography may damage exhibitions in museums.