REFLECTION OF LIGHT

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REFLECTION OF LIGHT:

Reflection is the bouncing back of light.

Types of reflections

a) Regular reflection

b) Irregular reflection

REGULAR REFLECTION:

1.     This is when light rays are bounced back in a regular direction.

2.     It takes place when a parallel beam meets a smooth and shiny surface and is reflected as a parallel beam.

3.     The surfaces include

        a) Plane mirrors

        b) Polished surfaces etc.

Rays of light on a smooth shiny surface.

smooth shiny surfare

IRREGULAR RELFECTION:

  1. This takes place when light meets rough opaque objects.
  2.  When a parallel beam meets a rough surface, the rays are reflected when they are scattered.
  3. The scattered reflection is known as diffused reflection.
  4. This type of reflection is common in rough surfaces like frosted glasses.
  5. We are unable to see clear images on  rough surfaces because they give irregular reflection.
rough surface

REFLECTION ON A SMOOTH SURFACE.

1      The ray of light from the source of light to the smooth surface is known as an incident Ray.

2      The ray of light bounced off from from the reflecting surface is known as reflected ray

3      The angle between the normal and the incident ray is called angle of incidence

  • The angle between the normal and Reflected ray is known as angle of Reflection.
reflection angles

LAWS OF REFLECTION:

The laws of reflection state that:

  • The ray of incidence, Normal and ray of reflection lie in the same plane at the point of incidence.
  • Angle of incidence equals to the angle of reflection.

REFLECTION AND ABSORPTION OF LIGHT BY DIFFERENT MATERIALS.

1.     Brightly coloured objects reflect more light and heat than dull coloured ones.

2.     Smooth and polished objects reflect more light and heat than rough and unpolished ones.

3.     Dark materials are good absorbers of light and heat.

4.     Black clothes dry faster than white because black absorbs more light and heat than white which reflect more heat and light.

5.     Food in a black sauce pan will cook faster than food cooked in a shinny sauce pan.

6.     Houses in hot areas should be painted with bright colours like white to reflect heat and keep the interior of the house cool.

7.     People living in hot areas prefer wearing brightly coloured clothes to dark coloured clothes because brite colours reflect heat to keep the body cool while dark ones absorb heat which makes one uncomfortable with heat.

IMPORTANCES OF REFLCTION

  • Reflection helps us to view objects. This is so because in order to view objects, light has to be reflected from the object to our eyes.
  • Reflection helps us to use mirrors to view our images and other images either behind or above us.
  • Helps in the making of solar cookers.
  • Reflection is useful in reflectors of car headlamps and torches to help to form a diverging  beam.

        IMAGES

  1. When the rays are from an object and fall on a plane mirror, they are reflected and form an image.

Types of Images

        There are two types of images and these are:

  1. Real images
    1. Virtual images.

REAL IMAGES

These are the images formed on the screen like:

  1. Televisions
  2. Cinemas
  3. Photographs.
  4. Computers

VIRTUAL IMAGES.

These are images formed behind the screen e.g. on mirrors.

Application of the characteristics of plane mirror images.

1

REFRACTION OF LIGHT:

  1. This is the bending of light rays as they pass from one media to another.
  2. Refraction is brought about by change in speed of light as it passes through transparent objects of different densities.
  3. A sudden change of speed of light leads to change in direction seen as a bend.
  4. When light passes from air to water it will bend because air is less dense than water.
glass

        i.      Incident ray.

        RR    Refracted ray

        ERR  Emergent refracted ray.

        a.     Angle of incidence.

        r.      Angle of refraction.

NOTE:

When rays are from less dense medium to a denser medium, it bends towards the normal.

When it moves from a denser to a less denser medium, it bends away from the normal.

EFFECTS OF REFRACTION:

  1. It makes pools of water appear shallower than they are.
    1. It makes a stick placed in a glass of water appear bent.
bent pencile

c)  It causes mirages on hot sunny days.

d)  It makes the white colour to split into the seven colours of the rainbow.

e)  A fish in water is seen to be nearer the surface of water than its actual depth due to refraction.

Advantages of Refraction:

  1. It enables the camera to focus images on the film.
  2. Enables optical instruments like microphones, telescopes to function.
  3. Enables eyes to focus images onto the retina.

Disadvantages of Refraction:

  1. It brings about short sightedness and long sightedness.
  2. It may cause accidents of drowning in pools of water when they are miss judged to be shallow.

SIMPLE OPTICAL INSTRUMENTS:

These are instruments that work with the help of light.

Examples of optical instruments

  1. Plane mirrors.
  2. Periscope
  3. Curved mirrors
  4. Lenses
  5. Camera
  6. Pinhole Camera
  7. Telescope
  8. Binoculars
  9. Magnifying glasses


PLANE MIRRORS:

1.     This is a flat, opaque smooth shiny piece of glass.

Characteristics of images formed on plane mirrors.

  1. They are virtual. Virtual images are images that cannot be formed on the screen.

They are formed behind the mirror.

  • They are laterally inverted ( changed left to right or has reversed sides)
  • Same distance behind the mirror as the as the object in front of the mirror.
  • It is the right way up.
  • Has the same colour, shape and size as the object.

USES OF PLANE MIRRORS:

  1. They are used by people as dressing mirrors to look at themselves.
  2. Mirrors are used by drivers to see traffic behind them.
  3. The are used in periscopes to view objects above the viewers level.

PERISCOPE

  1. A periscope is an instrument used to view things over obstacles and around corners.
  2. Periscopes are made up of plane mirrors placed at 45o facing each other.
  3.  The rays from the objects are reflected on to the first mirror. It is then reflected into the second mirror and then viewed by the viewer.
pericope

USES OF PERISCOPES

  1. Periscopes are used in submarines when under water to view object on the water surface.
  2. They are also used by soldiers hidden in trenches to view things above them.
  3. They are used by short or hidden spectators in stadiums to watch matches.
  4. They are used by minors to view what is on the ground.