Properties of Light
- Light is a form of energy that helps us see things around us.
- Luminous objects emit light, and non-luminous objects do not emit light.
- The three phenomenons of light observed in our daily life are reflection, refraction and dispersion.
- Objects can be categorised into three types depending on their interaction with light energy—transparent, translucent and opaque.
- A shadow always forms opposite to the light source. Every object makes shadows in the presence of sunlight.
- In this concept, we will study some properties of light.
Sources and Properties of Light
Question 1:
Explain Why Light Can Travel in Vacuum but Not Sound.
Answer:
- Light and sound energy are sources of energy that propagate as waves.
- Light energy does not require a medium to propagate, but sound energy needs a medium to propagate.
- So, light can travel in a vacuum, but sound cannot.
Question 2:
Is Water More Opaque Than Air?
Answer:
- Yes, water is opaquer than air because it is optically denser than air.
- It means that the speed of light is higher in the air than in the water.
Question 3:
What Is Refraction?
Answer:
- The bending of light rays when they travel from one medium to another is called refraction.
- It happens because the speed of light is different in different media.
Question 4:
What Is a Lens, and How Many Types of Lens Are There?
Answer:
A lens is an optical device made of transparent materials like glass that refracts light rays.
It can
focus
light to form an image.
Lenses can be categorised into two types—
- Concave lens: A concave lens is curved from both sides, thinner at the centre and thicker at the edges.
- Convex lens: A biconvex lens is curved from both sides but thicker at the centre and thinner at the edges.
Question 5:
Why Does a Rose Look Red in the Light of All the Colours?
Answer:
- A rose is an opaque object.
- It absorbs all light colours exc
Question 6:
What Is a Rainbow?
Answer:
- A rainbow is a multicolour arc that forms due to light dispersion through water vapours.
- A rainbow usually appears in the sky after rainfall.
- The colours in a rainbow are visible in the following sequence—violet-indigo-blue-green-yellow-orange-red, in short, VIBGYOR.
Human Eye
Question 1:
Mention the Difference Between Rod and Cone Cells?
Answer:
The differences between rod and cone cells are as follows—
| Rod cells | Cone cells |
|---|---|
| Rod cells are more in number. | Cone cells are fewer in number than rod cells. |
| Do not give colour vision. | Responsible for colour vision. |
| Present at the edges of the retina. | Present at the periphery of the retina. |
Question 2:
What Are Rhodopsin and Iodopsin?
Answer:
- Both rhodopsin and iodopsin are pigments that are present in the human eye.
- Rhodopsin is the pigment in rod cells, and iodopsin is the pigment in cone cells.
- The lack of these pigments causes night blindness.
Effects of Light
Question 1:
Do Shadows Change Throughout the Day?
Answer:
- Yes, shadows change throughout the day.
- The length of a shadow decreases from morning to afternoon and increases in the evening.
Question 2:
What Are the Properties of Shadow?
Answer:
The properties of a shadow are as follows:
- A shadow is always formed on the opposite side of the light source.
- A shadow is always black.
- The position of the shadow changes with the position of the light source.
- The size of the shadow depends on the distance between the object and the light source.
- As distance decreases, the size of the shadow increases.