LIGHTELECTROMAGNETIC WAVES

WHAT IS LIGHT ?

• We see light as color and brightness

• It’s actually electromagnetic radiation.

• Partly electric, partly magnetic• Flows in straight line (radiates)

Where does light come from?

• The Sun and the stars. • But how do they make light?• It all starts with ATOMS.• A nucleus surrounded by electrons

that orbit in the electron cloud.

Where does light come from?

• Electrons get kicked into a different orbit• This doesn’t happen very often in solar

systems, but it does in atoms• If you add energy to an atom (heat it

up), the electrons will jump to higher orbits.

• When an atom cools, electrons jump back to original orbits.

• As they jump back, they emit light, a form of energy.

Color of Light

• Each electron that jumps back emits one photon of light

• What color is this light?• Depends on how big the jump between

orbits was• The bigger the jump, the higher the energy.• The energy determines color; a blue photon

has more energy than a red• Shine all the colors together, you get white

light!

PHOTON

• A photon is a discrete bundle (or quantum) of electromagnetic (or light) energy. Photons are always in motion and, in a vacuum, have a constant speed of light to all observers, at the vacuum speed of light (more commonly just called the speed of light) of c = 2.998 x 108 m/s.

PHOTON

Reflection of light

• The incoming light wave is referred to as an incident wave, and the wave that is bounced away from the surface is termed the reflected wave.

Reflection of light

• Visible white light that is directed onto the surface of a mirror at an angle (incident) is reflected back into space by the mirror surface at another angle (reflected) that is equal to the incident angle, as presented for the action of a beam of light from a flashlight on a smooth, flat mirror.

Reflection of Light

Reflection of light

• To visualize the differences between specular and diffuse reflection, consider two very different surfaces: a smooth mirror and a rough reddish surface. The mirror reflects all of the components of white light (such as red, green, and blue wavelengths) almost equally.

Reflection of light

Reflection of light

• The reflected specular light follows a trajectory having the same angle from the normal as the incident light. The rough reddish surface, however, does not reflect all wavelengths because it absorbs most of the blue and green components, and reflects the red light. Also, the diffuse light that is reflected from the rough surface is scattered in all directions.

Concave mirrors

• Concave mirrors, commonly found in the largest optical telescopes, are used to collect the faint light emitted from very distant stars. The curved surface concentrates parallel rays from a great distance into a single point for enhanced intensity. The inside of a shiny spoon is a common example of a concave mirror surface, and can be used to demonstrate some properties of this mirror type.

Concave mirrors

Convex Mirrors

• Another common mirror having a curved-surface, the convex mirror, is often used in automobile rear-view reflector applications where the outward mirror curvature produces a smaller, more panoramic view of events occurring behind the vehicle. When parallel rays strike the surface of a convex mirror, the light waves are reflected outward so that they diverge.

Convex Mirrors

• Convex mirrors are also used as wide-angle mirrors in hallways and businesses for security and safety. The most amusing applications for curved mirrors are the novelty mirrors found at state fairs, carnivals, and fun houses. These mirrors often incorporate a mixture of concave and convex surfaces, or surfaces that gently change curvature, to produce bizarre, distorted reflections when people observe them.

Refraction

•Refraction of Light

• When electromagnetic radiation, in the form of visible light, travels from one substance or medium into another, the light waves may undergo a phenomenon known as refraction, which is manifested by a bending or change in direction of the light

Refraction

• The effects of refraction are responsible for a variety of familiar phenomena, such as the apparent bending of an object that is partially submerged in water and the mirages observed on a hot, sandy desert. The refraction of visible light is also an important characteristic of lenses that enables them to focus a beam of light onto a single point.

Refraction

Refraction

Refraction

Refraction

Refraction