Concept: Effects of Light
Reflection on a plane mirror:
- A plane mirror is a regular smooth surface that is a perfect object for reflection.
- The image formed after reflection through a plane mirror has the following characteristics—
- Same size as that of the object.
- On the other side of the mirror.
- Virtual and erect.
- Laterally inverted.
- The phenomenon of reversal of mirror image that makes the right side of an object appear as left and left side of an object to appear as right is called lateral inversion.
Formation of a shadow:
- A dark spot formed by blocking the path of light by an opaque object is called a shadow.
- The shape of the shadow resembles the shape of the object.
- Requirements for shadow formation
- A source of light.
- An opaque or a translucent object.
- A screen on which the shadow can be obtained.
- Properties of a shadow:
- A shadow is formed in the opposite direction of the light source.
- The shadow is always black irrespective of the object’s colour.
- The details of the object cannot be observed in its shadow; only the outline structure is visible.
- The size of the shadow varies based on the following factors—
- Distance between the source of light and object.
- Distance between the screen and the object.
- Size of the object and source of light.
Occurrence of day and night:
- The occurrence of day and night depends on the rotation of earth.
- Earth makes one complete rotation on its axis in 24 hours.
- The day exists in the part of the earth that faces the sun, and simultaneously the part that faces away from the sun experiences night.
Formation of an eclipse:
An eclipse is a natural phenomenon in space when one celestial object obstructs another from view.
There are two types of the eclipse—solar eclipse and lunar eclipse.
- It occurs when the sun, earth and moon all come in a straight line where the moon lies in between the sun and earth.
- The moon lying in the centre blocks the light from the sun and makes a shadow on Earth which acts as a screen.
- A lunar eclipse occurs when the sun, earth and moon come in a straight line where the earth lies in the centre.
- The earth blocks the light from the sun, and its shadow falls on the moon, making it invisible.
Dispersion of light:
- Prism is a transparent polyhedron used to study the dispersion of light.
- When normal/white light passes through a prism, it disperses into seven colours when it comes out on the other side of the prism.
- The same phenomenon happens when a rainbow is formed. The tiny droplets of water act as a prism and disperse the white light in seven colours—violet, indigo, blue, green, yellow, orange and red.
Rotation: A circular motion of an object on its axis.
Celestial: Something related to the sky or outer space.
Did You Know?
- The sundial was used before the invention of clocks. It worked based on shadows cast by the sun during the daytime. The world’s biggest stone sundial is located at Jantar Mantar in Jaipur.
- A solar eclipse is of four types—partial solar eclipse, annular solar eclipse, total solar eclipse and hybrid solar eclipse.
- A lunar eclipse can last for more than one hour.
- Animals behave in a puzzled manner during solar eclipses. Animals that are active during the day return to their nighttime homes, and the nocturnal animals think they have overslept.