Chapter 7: Rays and Waves

Light Rays and Waves

Features of Light

  • Is a form of radiation.
  • ==They travel in straight line and in form of transverse wave.==
  • Transfers energy when materials absorb light.
  • They can travel in empty spaces/vacuum.
  • Nothing can travel faster then light.

Reflection in plane mirrors

Laws of Reflection

  • ==The angle of incidence is equal to the angle of reflection.==

  • ==The incident ray, the reflected and the normal all lie in the same plane.==

Images formed in a plane mirror

  • This image is ^^laterally inverted.^^

Finding the position of an image in a mirror

Points to keep in mind for image size and position

  • ==When a plane mirror forms an image:==
    • image is the same size as the object
    • image is as far behind the mirror as the object is in front.
    • a line joining equivalent points on the object and image passes through the mirror at right angles.

Refraction of Light

==Refraction is the change in speed of a wave crossing a boundary between two media, resulting in a change in direction.==

  • As shown below:

  • Also explained as:

  • When light enters a ^^more optically dense medium^^, the angle of incidence is greater than the angle of refraction.

    • The opposite is true when light enters a less optically dense medium.

Refractive Index

==The refractive index== ==n== ==of a medium is defined as the ratio between the speed of light in two different mediums.==

  • It is calculated with the use of following equation:

Refraction by Prism

==When light enters a glass prism it splits into seven colours (when light exists).==

  • This range of colors is known as spectrum.

==This effect is called== ==dispersion.==

  • Easy way to remember these colors is using the mnemonic Roy G Biv.
    • Red
    • Orange
    • Yellow
    • Green
    • Blue
    • Indigo
    • Violet

Total Internal Reflection

  • At a certain angle of incidence called the critical angle, the ^^light will travel along the boundary between the two media.^^
  • Total internal reflection occurs when the ^^angle of incidence is greater than the critical angle and the light reflects back into the medium.^^
  • For total internal reflection to occur, the ^^light must also be travelling from a more optically dense medium into a less optically dense medium (most common example is glass to air).^^
  • The critical angle can be related to the refractive index by the equation:

Common Uses of Reflecting Prisms

  • Periscope
  • Rear Reflectors
  • Binoculars
  • Optical FIbres

Lenses

  • Two main kinds:

    1. {{Convex/Converging Lens{{
    • thickest in the middle and thin round the middle.
    • when rays are parallel they pass through the lens and are bent inwards.
    1. {{Concave/Diverging Lens{{
    • thin in the middle and thickest round the edge.
    • when rays parallel to the principal axis pass through the lens, they are bent outwards/they are spread out.

Terms

  • ==The point where rays meet the lens is called== ==principal focus.==
    • Its distance from the center of the lens is called focal length.

Images formed by convex lenses

Images formed by concave lenses

Common Uses of Lens in daily life

  • Camera
  • Human eye
  • Projector

Electromagnetic Waves

  • Light waves is one of the example.

  • Common features:

    • they can travel through vacuum, at a speed of 300 000 kilometers per second.
    • they are transverse waves.
    • they transfer energy. A material gains energy when they it absorbs it.

Electromagnetic Spectrum

Radio Waves

  • ==Can be produced artificially by making a current oscillate in a transmitting aerial.==
  • Commonly used to transmit TV pictures.

Infrared Radiation and Light

  • All objects radiate infra red due to the motion of their atoms or molecules.
  • As an object heats up, it radiates more and more infrared, and shorter wavelengths.
  • ==Short wavelength infrared is often== ==called== =='infrared light', even though it is invisible.==

Ultraviolet Radiation

  • Sun’s ultraviolet radiation is harmful to living cells - can cause skin cancer.
  • Ultraviolet rays are harmful to living cells - commonly used to sterilize medical equipment.

X-rays

  • Are given off when fast moving electrons lose energy quickly.
  • In engineering or in medical - they are used to detect flaws inside the material or a damaged bone.
  • They can be dangerous because they damage living cells deep in the body and can cause cancer or mutations.

Gamma Rays

  • Come from radioactive materials.
  • Are produced when an unstable nuclei of unstable atoms break up or lose energy.