Nature of Light–9th Standard Science Question Bank

Choose the right answer .

1.The packets fo energy are called ------------

a. Electrons b. neutrons c. Photons d. Positrons

2. Corpuscles are the tiny particles of ----------

a. light b. sound c. waves d. radiation

3. Which of the formula represents the energy of photon ------------

a. E = hc/λ b. E =λ/hc c. E = h/λc d. E = h/λ

Fill in the blanks with right answer

1.Light has --------------and --------------------nature. ( corpuscles wave )

2. Light waves travel in the form of --------------------waves.( electromagnetic )

3. Electromagnetic waves are ------------------- waves. ( transverse )

Match the followings :

1. Corpuscular - theory Maxwell (3)

2. Wave theory - Max plank (4)

3. Electromagnetic theory - Huygens (2)

4. Quantum theory - Newton (1)

Answer the following questions

1.What is Light ? Mention the theories discussed related to the nature of light.

Light is a form of energy. Theories discussed related to the nature of light are Corpuscular theory of Newton, Wave theory of Huygens, Electromagnetic theory of Maxwell and Quantum theory Max Plank.

2. Explain Corpuscular theory of Newton.

This theory says light consists of a stream of extremely light & tiny particles called corpuscles.

3. Mention the merits & demerits of Corpuscular theory.

This theory explains reflection, refraction and dispersion of light but failed to explain diffraction , interference & polarisation characteristics.

4. Explain Wave theory of Huygens

According to this theory light travels in the form of mechanical waves. Light travel in the ether medium in the form of waves. light energy is carried by the waves caused by vibration of ether particles.

5. Mention the merits & demerits of Wave theory of Huygens.

This theory explains reflection, refraction and dispersion, diffraction , interference characteristics of light but failed explain the existence of ether medium.

6. Explain Electromagnetic theory of Maxwell.

According to this theory light travel in the form of electromagnetic waves. These electromagnetic waves are transverse waves, do not require a material medium for transmission. These waves travel through vacuum also.

7. Mention the merits & demerits of Electromagnetic theory of Maxwell.

This theory explains reflection, refraction and dispersion, diffraction , interference characteristics of light but failed explain black body radiation spectrum and photoelectric effect.

8. Explain Quantum theory Max Plank.

According to this theory light consists of discrete units called as packets of energy. These tiny packets of energy are called as Quanta or Photons. This theory explain all the properties of light.

9. Write the equation of energy of photon .

E = hc/λ or E = hγ

Here E = energy of photon c = velocity of light (3 X 10 8 m/s)

λ = wave length , γ = frequency ,

h = plank’s constant ( 6.626 X 10 –34 J.s)

10. Explain dual nature of light.

To explain all the properties of light , we conclude that light energy is propagated in the form of particles having wave nature . This is called dual nature of light.

11. Which theory of light proposed the presence of ether medium for propagation of light.

Wave theory of Huygens proposed the presence of ether medium for propagation of light.

12. Which theory explains all the characteristics of light ?

Quantum theory Max Plank explains all the characteristics of light.

13. What is electromagnetic radiation ?

Radiations like light, x-rays, gamma rays & infrared rays are called electromagnetic radiation