# Reflection and Refraction of Light – Physics

## REFLECTION OF LIGHT

Light is a form of energy that causes the sensation of vision. There are natural and artificial sources of light.

1. Natural Sources: Sun, stars etc…
2. Artificial Sources: Bulbs, fluorescent tubes, candles, lamps, torches, arc light etc…

LUMINOUS OBJECTS: These are objects that generate and emit light by themselves. Examples are the sun, stars, fireflies, some deep-sea fishes etc…

NON LUMINOUS OBJECTS: These are objects that depend on luminous objects to illuminate them. We cannot see them until they reflect light from luminous objects. Examples are The moon, road signs, bricks, our bodies, books, clothes etc…

### RAYS AND BEAMS

A ray is a direction that lights energy travels. Rays are not real but imaginary lines. A beam is a collection of rays.

### TYPES OF BEAMS

PARALLEL BEAM: This is a beam in which the rays are parallel to each other. Searchlights give off parallel beam. DIVERGENT BEAM: This is a beam in which the rays spread from the source. Examples are the sun, lamps, and bulbs produce divergent beams. CONVERGENT BEAM: This is one in which the rays meet at a point. A hand lens produces a convergent beam. ### PRINCIPLE OF REVERSIBILITY OF LIGHT

It states that the path of light is reversible and rectilinear propagation of light is the phenomenon of light traveling in a straight line.

### REFLECTION OF LIGHT AT PLAIN SURFACES

Reflection is the bouncing off of light from a surface. When light falls on a surface, three things happen to it;

• It is reflected. (Bounced back)
• It is transmitted. (Passes through)
• It is absorbed. (Consumed or swallowed)

### TYPES OF REFLECTION

REGULAR OR SPECULAR REFLECTION: This occurs when parallel rays of light incident on a smooth surface are reflected as parallel rays in one direction. For there to be this kind of reflection, the reflecting surface must be smooth relative to the wavelength of light. IRREGULAR OR DIFFUSED REFLECTION: This is also called scattered reflection. It is a type of reflection in which a parallel rays incident on a rough surface is reflected various directions.

The mirror gives a regular reflection, while the skin, pages of a book and clothes etc… leads to irregular reflection. ### LAWS OF REFLECTION

• The incident ray, the reflected ray and the normal at the point of incidence, all lie on the same plane.
• The angle of incidence is equal to the angle of reflection.

### IMAGES FORMED BY A PLAIN MIRROR

A mirror is a glass made opaque on one side. The image formed by a mirror has the following characteristics. The image is:

• Erect (standing upright).
• Same size as the object.
• Of the same distance as the object from the reflecting surface.
• Virtual (because it is formed behind the mirror).
• Laterally inverted.

### REFLECTION AT CURVED SURFACES

There are two types of curved mirrors namely

1. Concave Mirror
2. Convex Mirror

### PARTS OF A MIRROR

1. Pole
2. Focal point
3. Principal axis
5. Centre of curvature
6. Aperture
7. Principal focus

NOTE:

• For a concave mirror, F is positive while for a convex mirror, F is negative.
• A virtual image is one that cannot be caught on a screen. A real image is one that can be caught on a screen.
• Magnification (m) is the ratio of the size of the image to the size of the object.  m = v/u
• Mirror formula is1/f = 1/v + 1/u

Where: F = Focus length, V = Image distance, and U = Object distance.

## REFRACTION OF LIGHT

This is the bending of a light ray as it crosses the bonding between two media of different densities thus causing a change in direction.

### LAWS OF REFRACTION

1. The incident ray, the refracted ray and the normal at the point of incidence all lie on the same plane.
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media. This is called Snell’s law.

### CRITICAL ANGLE

This is the angle of incidence in the denser medium when the angle of refraction in the less dense medium is 90

### TOTAL INTERNAL REFLECTION

This occurs when light traveling from a region of a higher refractive index to a region of lower refractive index strikes the boundary at an angle greater than the critical angle such that all light reflects back into the region of the higher refractive index.

OR

Total Internal Reflection is the reflection of an incident ray of light at the interface between the medium of incidence and another medium of a lower refractive index when the angle of incidence in the denser medium exceeds the critical angle.

### APPLICATION OF TOTAL INTERNAL REFLECTION

1. Reflecting prism.
2. TIR of radio waves in the Appleton layer of the atmosphere.
3. Mirage.
4. Optic Fibre.
5. Field of view of fish in the water.

## LENSES

A lens is a transparent material that is used to focus light and form an image.

### TYPES OF LENSES

A Convex lens is thicker at the center than at the edges. It is also called a Converging lens.

A Concave lens is thinner at the center than at the edges. It is also called a Diverging lens.  ### USES OF LENSES

1. Spectacle glasses.
2. Contact lenses.
3. Microscopes
4. Telescopes.
5. Cameras.
6. Projectors.

### LENS DEFECTS

• Chromatic Aberration.
• Spherical Aberration.