NEET 2022 | Class 12

NEET Important Chapter - Dual Nature of Matter and Radiation

Get plus subscription and access unlimited live and recorded courses
Dual Nature of Matter and Radiation for NEET Preparation

Dual Nature of Matter and Radiation for NEET Preparation

Just like most of the chapters in part 2 of physics of class 12, the dual nature of matter and radiation also plays an important role in the NEET exam. The chapter revolves around the microscopic behaviour of particles and light. 


The dual nature of matter and radiation starts with the electron emission and photoelectric effect. Moving further, we study the history of the photoelectric effect with the explanation of various experiments performed by a few great physicists. The experimental setup of the photoelectric effect lets us understand the phenomena. With the help of an experimental set-up, we study a few important topics such as photocurrent and stopping potential.


In the chapter dual nature of light and radiation, we got introduced to wave theory. In wave theory, we come across a few remarkable concepts such as wave nature of matter, energy function, etc… In the wave theory of matter, we find the most significant discoveries by De Broglie. We study the De Broglie hypothesis to understand the dual nature of light. In this chapter, we also come across the uncertainty principle, Davisson Germer's experiment.


In this article, we will be focusing on the concepts of the dual nature of matter and radiation that plays a vital role in the NEET exam.


Important Topics of Dual Nature of Matter and Radiation

  • Photoelectric effect

  • Work function

  • Threshold frequency

  • Relation between Potential and Photoelectric Current

  • Relation between Intensity of the Incident Light and Photoelectric Current

  • Electron emission

  • Cathode rays

  • De Broglie equation

  • Wave nature of matter


Important Concepts of Dual Nature of Matter and Radiation

We know that in a chapter there will be many concepts that are being mentioned in the textbook, but when it comes to NEET preparation we have to focus on what is most important among all the concepts in the chapter. Below is the table provided for some most important concepts of the dual nature of matter and radiation.

Sl. No

Name of the Concept

Key Points of Concept

1.

Electron emission

The electrons present on the surfaces of the metal are emitted by the process of electron emission.


There are basically three types of electron emission:

  1. Thermionic Emission: In this process, the metallic surface is sufficiently heated with thermal energy till the electrons are able to freely depart the surface.


  1. Field Emission: To emit electrons, an extremely strong electric field is applied to the metal surface.


  1. Photoelectric Emission: Photoelectric emission occurs when electromagnetic radiation (such as light) of a sufficient frequency impacts a metallic surface and lights it for the emission of electrons.

2.

Photoelectric effect

  • The phenomenon of the photoelectric effect revolves around electron emission.

  • The photoelectric effect shows that when light radiation is incident on a metallic surface, the electrons near the surface absorb the radiation energy and get liberated from the surface.

  • These photo or light generated electrons are known as photoelectrons.

3.

Work function and Threshold frequency

  • Work function: It is the minimum amount of energy required for an electron to emit from the metal surface. It is denoted by the letter “W” and measured in terms of “eV”.

  • Threshold frequency: It is the minimum frequency required for the emission of electrons. It is denoted by ${\nu_o}$.

4.

Relation between Potential and Photoelectric Current

  • With an increase in the accelerating potential, the photoelectric current increases equally.

  • The saturation current occurs when the photoelectric current reaches its maximum value.

  • All photoelectrons are emitted from the emitter and reach the collection plate when the photoelectrons reach saturation.

5.

Relation between Intensity of the Incident Light and Photoelectric Current

  • Photocurrent does not occur if the frequency of the incident radiation or light is lower than the metal surface's minimum frequency. It rapidly declines until it reaches zero, which is also known as the cut-off frequency or the metal plate's stopping potential.

  • The photoelectric current's cut-off frequency, or stopping potential, is essentially a physical feature of the metal plate.

  • The photocurrent becomes zero or reaches the cut-off frequency only when the stopping potential is sufficient to drive back even the highest-energy photoelectric particles approaching with maximum kinetic energy.

6.

De Broglie hypothesis- dual nature of light

  • De Broglie theory suggests that light behaves like both particles and waves. I.e., dual behaviour of matter

  • According to De Broglie's hypothesis, the wavelength associated with momentum is too small, which explains why microscopic elements do not exhibit wave characteristics.

7.

Heisenberg's Uncertainty principle

  • The uncertainty principle states that it is impossible to measure both position and momentum of the electron simultaneously.

  • There will be some uncertainty in the specification of position (∆ x) and some uncertainty in the specification of momentum (∆p).

${\Delta x}.{\Delta p}\approx\hbar$


List of Important Formulae of Dual Nature of Matter and Radiations

Now, let us have a look at a few important dual nature of radiation and matter formulas that will be helpful in solving questions from this chapter.

Sl. No

Name of Concept

Formula

1.

De Broglie wavelength

$\lambda=\dfrac {h}{p}$

Or

$\lambda=\dfrac {h}{\sqrt {2mE}}$

2.

Photon energy

$E=h\nu=\dfrac {hc}{\lambda}$

3.

Einstein’s photoelectric equation and Work function

${E_k}=h\nu-\phi$

Where,

$\phi$- The work function

4. 

Threshold frequency

${\nu_o}=\dfrac {\phi}{h}

5.

The momentum of photon

The energy of photon moving with momentum p is $E=p c$ 

Therefore, momentum p is given by:

$p=\dfrac {h \nu}{c}$ 


Solved Examples of Dual nature of Matter and Radiations

1. All electrons emitted from a metal surface by an incident light of wavelength 100 nm can be stopped just before travelling 2 m in the direction of uniform electric field of 6 N/C. Then the work function of the surface is

  1. 0.5 eV

  2. 2.2 eV

  3. 0.3 eV

  4. 0.4 eV

Sol:

Given, 

The wavelength of incident light=$\lambda$= 100 nm

The electrons ejected by the metal surface are stopped by the electric field of 6 N/C at a distance 2m.

Now, we are asked to determine the stopping potential of the electrons. Let us assume that the electrons are travelling with a maximum speed Vmax. Then we write:

${k_{max}}=\dfrac {1}{2} m {v^2}=e E d$

${k_{max}}=\dfrac {e\times 6 \times 2}{e}=12 eV$

The energy of incident photo is:
$E=h \nu=\dfrac {hc}{\lambda}=\dfrac {1240 nm eV}{100}= 12.4 eV$

From Einstein's photoelectric equation we have:

${E_k}=h \nu -\phi$

Where,

$\phi$- The work function

${k_{max}}=h \nu -\phi$

$\phi = 12.4-12=0.4 eV$

Therefore, option d is the correct answer.

Key point: While calculating the maximum kinetic energy we should not forget to convert it in terms of eV.


2. The threshold frequency for photoelectric effect on sodium corresponds to a wavelength 8000 Å. Its work function is?

Sol:

Then work function of an emitted electron will be

$\phi= {\nu_o}{h}=\dfrac {hc}{\lambda}$

$\phi =\dfrac {6.6\times {10^{-34}} \times 3 \times {10^8}}{8000\times {10^{-10}}}$

$\phi=2.475\times {10^{-19}} joules$

Key point: We need to modify the formula according to the given data. We know that the work function is written in terms of threshold frequency but here we were given threshold wavelength. We need to use the relation between frequency and wavelength to solve this problem.


Previous Year Questions from Dual Nature of Matter and Radiations

1. The number of photons per second on an average emitted by the source of monochromatic light of wavelength 600 nm, when it delivers the power of $3.3 \times {10^{-3}}$ watt will be: (NEET 2021)

  1. ${10^16}$

  2. ${10^15}$

  3. ${10^18}$

  4. ${10^17}$

Sol:

Given,

Wavelength of source of monochromatic light=$\lambda$= 600 nm

Power radiated by the source=$3.3 \times {10^{-3}}$ watt

The energy of the photon=E=$\dfrac {hc}{\lambda}= 3.3 \times {10^{-19}} Joules$

Let n is the number of photons emitted per second such that the energy emitted in one second is $3.3 \times {10^{-3}}$ J.

Thus, we get:

nE=$3.3 \times {10^{-3}}$

$n=\dfrac {3.3 \times {10^{-3}}}{3.3 \times {10^{-19}}}={10^16}$

Therefore, option A is the right answer.

Trick: Use the formula $P=\dfrac {nhc}{\lambda}$ to arrive at the solution easily.


2. Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled? (NEET 2020)

  1. Four times

  2. One-fourth

  3. Zero

  4. Doubled

Sol: 

Given,

Frequency of light=$\nu= 1.5 {\nu_o}$

Now, it is said that the frequency is halved, i.e., ${\nu}’ = \dfrac {1.5 {\nu_o}}{2}=0.75 {\nu_o}$

Since, 0.75 𝝼o < 𝝼o, .e. f' is less than threshold frequency, zero current will flow.

Therefore, option C is the right answer.

Key point: Current will flow if and only if threshold frequency is less.


Practice Questions

  1. 1.5 mW of 400 nm light is directed at a photoelectric cell. If 0.1% of the incident photons produce photoelectrons, the current in the cell is (Ans: 0.48 µA)

  2. The frequency of incident light falling on a photosensitive plate is doubled, and then the maximum kinetic energy of the emitted photoelectrons will become? (Ans: More than 2 times of the earlier value)


Conclusion

In this article we have discussed the dual nature of matter and radiation chapter with respect to the NEET exam. In this article we have provided solved examples, previous year questions, important formulae list, etc.

See More
NEET Important Dates

NEET Important Dates

View All Dates
NEET 2022 exam date and revised schedule have been announced by the NTA. NEET 2022 will now be conducted on 17-July-2022, and the exam registration closes on 20-May-2022. You can check the complete schedule on our site. Furthermore, you can check NEET 2022 dates for application, admit card, exam, answer key, result, counselling, etc along with other relevant information.
See More
View All Dates
NEET Information

NEET Information

Application Form
Eligibility Criteria
Reservation Policy
Admit Card
NTA has announced the NEET 2022 application form release date on the official website https://neet.nta.nic.in/. NEET 2022 Application Form is available on the official website for online registration. Besides NEET 2022 application form release date, learn about the application process, steps to fill the form, how to submit, exam date sheet etc online. Check our website for more details.
NEET 2022 applicants should be aware of the eligibility criteria before applying to the exam. NTA has released all the relevant information on the official website, i.e. https://neet.nta.nic.in/. NEET 2022 aspirants should have passed Class 12th or any other equivalent qualifying examination in 2021, 2020, or students appearing in the Class 12th final exam in 2022 can also apply. For further details, visit our website.
As per the union government’s norms, NTA has released the NEET 2022 reservation criteria for different candidates’ categories (SC/ST/OBC/PwD), All India Quota, State Government Quota, Deemed Universities, and more. You can check more details on Vedantu website.
NEET 2022 Admit Card will be released by the NTA in the month of June 2022. Candidates can download the NEET admit card and hall ticket from the NEET official website i.e. https://neet.nta.nic.in/. For more details on the NEET admit card 2022, candidates can check Vedantu official website.
NEET 2022 Study Material

NEET 2022 Study Material

View NEET Syllabus in Detail
Download full syllabus
Download full syllabus
View NEET Syllabus in Detail
NEET 2022 Study Material

NEET 2022 Study Material

View all study material for NEET
All
Physics
Chemistry
Biology
See All
NEET Question Papers

NEET Question Papers

NEET 2022 Book Solutions and PDF Download

NEET 2022 Book Solutions and PDF Download

View all NEET Important Books
Biology
NCERT Book for Class 12 Biology
Physics
NCERT Book for Class 12 Physics
Chemistry
NCERT Book for Class 12 Chemistry
Physics
H. C. Verma Solutions
See All
NEET Mock Tests

NEET Mock Tests

View all mock tests
"NEET 2022 free online mock test series for exam preparation are available on the Vedantu website for free download. Practising these mock test papers of Physics, Chemistry and Biology prepared by expert teachers at Vedantu will help you to boost your confidence to face the NEET 2022 examination without any worries. The NEET test series for Physics, Chemistry and Biology that is based on the latest syllabus of NEET and also the Previous Year Question Papers."
See More
NEET 2022 Cut Off

NEET 2022 Cut Off

NEET Cut Off
NTA is responsible for the release of the NEET 2022 cut off score. The qualifying percentile score might remain the same for different categories. According to the latest trends, the expected cut off mark for NEET 2022 is 50% for general category candidates, 45% for physically challenged candidates, and 40% for candidates from reserved categories. For the general category, NEET qualifying marks for 2021 ranged from 720-138 general category, while for OBC/SC/ST categories, they ranged from 137-108 for OBC, 137-108 for SC and 137-108 for ST category.
See More
NEET 2022 Results

NEET 2022 Results

The NEET 2022 result is published by NTA on https://neet.nta.nic.in/ in the form of a scorecard on 7-Sep-2022. The scorecard will include the roll number, application number, candidate's personal details, and the percentile, marks, and rank of the candidate. Only those candidates who achieve the NEET cut-off will be considered qualified for the exam.
See More
Rank List
Counselling
Cutoff
NEET 2022 state rank lists will be released by the state counselling committees for admissions to the 85% state quota and to all seats in private medical and dental colleges. NEET 2022 state rank lists are based on the marks obtained in entrance exams. Candidates can check the NEET 2022 state rank list on the official website or on our site.
The NTA will conduct NEET 2022 counselling at https://www.mcc.nic.in/. There will be two rounds of counselling for admission under All India Quota (AIQ), deemed and central universities, AIIMS, JIPMER, ESIC, and AFMC. A mop-up round of NEET counselling will be conducted excluding 15% AIQ seats, while the dates of NEET 2022 counselling for 85% state quota seats will be announced by the respective state authorities.
NTA is responsible for the release of the NEET 2022 cut off score. The qualifying percentile score might remain the same for different categories. According to the latest trends, the expected cut off mark for NEET 2022 is 50% for general category candidates, 45% for physically challenged candidates, and 40% for candidates from reserved categories. For the general category, NEET qualifying marks for 2021 ranged from 720-138 general category, while for OBC/SC/ST categories, they ranged from 137-108 for OBC, 137-108 for SC and 137-108 for ST category.
Want to know which Engineering colleges in India accept the NEET 2022 scores for admission to Engineering? Find the list of Engineering colleges accepting NEET scores in India, compiled by Vedantu. There are 1622 Colleges that are accepting NEET. Also find more details on Fees, Ranking, Admission, and Placement.
See More
question-image

FAQs on NEET Important Chapter - Dual Nature of Matter and Radiation

FAQ

1. How many questions come from the dual nature of Radiation and matter in NEET?

Dual nature of matter and radiation is having high importance in the NEET exam, it carries nearly 2-3 questions with a weightage 4%.

2. Which chapter is the dual nature of Radiation and matter?

Dual Nature of Radiation and Matter is a chapter of class 12 and chapter 11.

3. Which chapter has more weightage in NEET?

Modern Physics, from the class 12th syllabus, is the most important topic for NEET. Current Electricity & Magnetism, Electrostatics and Optics are also very important chapters for NEET.