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# NCERT Class 12 Physics Chapter 11 - Dual Nature and Radiation of Matter - PDF Download

The dual nature of matter and radiation class 12 describes the duality in nature of matter, namely particle and wave. Phenomena like diffraction, interference and polarisation are part of the wave nature of light. You will also learn about the Compton effect and photoelectric effect where energy-momentum exchange and radiation behave as particles known as a photon.

Further, in NCERT solutions for class 12 physics chapter 11, there is an explanation on electrons released from the surface of metals due to the photoelectric effect. De Broglie equation says that a beam of electrons can be diffracted as a beam of light. There is an in-depth clarification of Einstein's photoelectric equation, Davisson and Germer experiment, Hertz's observation, Hallwachs’ and Lenard's experiment.

## Topics in Chapter 11 Dual Nature of Radiation and Matter

1. Introduction

2. Electron Emission

3. Photoelectric Effect

1. Hertz’s observations

2. Hallwachs and Lenard’s observations

4. Experimental Study of Photoelectric Effect

1. Effect of intensity of light on photocurrent

2. Effect of Potential on photoelectric current

3. Effect of frequency of incident radiation on stopping potential

5. Photoelectric Effect and Wave Theory of Light Ex.

6. Einstein’s Photoelectric Equation: Energy Quantum of Radiation

7. Particle Nature of Light: The Photon

8. Wave Nature of Matter

### Electron Emission

Electron emission is the removal of an electron from the surface of matter. As we know that the electrons are attracted to the protons in the nucleus of an atom. And this attraction holds the electrons in place. But if the electrons gain sufficient energy from an external source, the electrons can escape or void the metal surface.

### Photoelectric Effect

In the photoelectric effect, a low energy gamma photon that collides with an atom can transfer all of its energy to an inner orbital electron and that causes the ejection of the electron from the atom. The amount of energy required to eject the electron depends on the atomic number of objects.

#### Hertz’s Observations

Heinrich Hertz made the observation in 1887 that when light strikes a metal surface, certain electrons close to the surface can absorb enough energy from the incoming radiation to overcome the attraction of the positive ions in the surface material.

Hallwachs and Lenard’s Observations

Hallwachs and Lenard observed that when the light fell on the emitter plate, no electrons were emitted at all when the frequency of the incident light was smaller than a certain minimum value. This frequency is called threshold frequency. He also noticed that different metals have different threshold frequencies.

### Effect of Intensity of light On Photocurrent

The intensity of light is directly proportional to the photocurrent emitted per second. It means when the intensity of light increases, the photocurrent increases also. If the potential is positive, the photoelectric current increases.

### Effect of Potential on Photoelectric Current

Effect of Potential on Photoelectric Current For a fixed frequency and intensity of incident light, the photoelectric current increases with increase in the potential applied at the collector. When all the photoelectrons reach the plate A, current becomes maximum; it is called saturation current.

### Effect of Frequency of Incident Radiation On Stopping Potential

The stopping potential can vary with frequency of incident light. An increase in frequency of the incident light will increase the kinetic energy of the emitted electrons, hence greater retarding potential is needed to stop them.

### Photoelectric Effect and Wave Theory of Light

Photoelectric effect is a phenomenon in which electrically charged particles are released from or within a substance when it absorbs electromagnetic radiation.

Wave theory states that a light source emits light waves that spread in all directions. When the waves hit the mirror, they are reflected depending on the arrival angle, but each wave is turned back to the front to create a reversed image.

### Einstein’s Photoelectric Equation: Energy Quantum of Radiation

The photoelectric effect is based on the quantum theory of radiation.

1) The photocurrent is directly proportional to the intensity of incident radiation and it also increases with the collector plate potential to a certain limit until it reaches the saturation current.

2) The magnitude of stopping potential and then the maximum kinetic energy of emitted photoelectrons is proportional to the frequency of emitted radiation.

### Particle Nature of Light: The Photon

We can summarize the photon picture of electromagnetic radiation as mentioned below

(i) In interaction of radiation with matter, radiation acts as if it is made up of particles called photons.

(ii) Each photon has energy E and momentum p and speed c, the speed of light.

(iii) All photons of light of a particular frequency, or wavelength, have the same energy and momentum, whatever the intensity of radiation may be. As we increasing the intensity of light of a given wavelength, there is only an increase in the number of photons per second crossing a given area, with each photon having the same energy. So, photon energy is independent of intensity of radiation.

(iv) Photons are electrically neutral and are not deflected by electric and magnetic fields and they can be destroyed or created when radiation is absorbed or emitted, respectively.

(v) In a photon collision (such as photon-electron collision), the total energy and total momentum are conserved. However, the number of photons may not be conserved in a collision. The photon may be absorbed or a new photon can be created.

### Wave Nature of Matter

The significance of the de Broglie relationship is that it proved mathematically that matter can  behave like a wave. In layman's terms, the de Broglie equation says that every moving particle – microscopic or macroscopic –has their own wavelength. For microscopic objects, the wave nature of matter is observable.

### Benefits of Dual Nature of Matter and Radiation Class 12 NCERT Solutions

• In chapter 11 solution you will get Images and diagrams for step by step explanation.

• Our expert Physics teachers elaborate examples and definitions.

• These solutions are designed in a very easy to understand language.

• All the experiments done by scientists in this chapter explained well.

Q1 What are the topics and subtopics covered under Chapter 11 of NCERT Solutions for Class 12 Physics?

Answer : The topics and subtopics covered under Chapter 11 of NCERT Solutions for Class 12 Physics are mentioned below:

• Introduction

• Electron Emission

• Photoelectric Effect

• Hertz’s Observations

• Hallwachs and Lenard’s Observations

• Experimental Study of Photoelectric Effect

• Effect of Intensity of Light on Photocurrent

• Effect of Potential on Photoelectric Current

• Effect of Frequency of Incident Radiation on Stopping Potential

• Photoelectric Effect and Wave Theory of Light Ex

• Einstein’s Photoelectric Equation: Energy Quantum of Radiation

• Particle Nature of Light: The Photon

• Wave Nature of Matter

Q2 What is quantum concept of radiation

Answer : Photoelectric effect can explained by the quantum concept of radiation.

1) The photocurrent is directly proportional to the intensity of incident radiation and it also increases with the collector plate potential to a certain limit until it reaches the saturation current.

2) The magnitude of stopping potential and then the maximum kinetic energy of emitted photoelectrons is proportional to the frequency of emitted radiation.