Just like most of the chapters in physics, Dual Nature of Matter & Radiation holds equal importance in the NEET exams. Every year around 2 questions are asked from this chapter and it alone holds about 4 -5 percent weightage in physics. Besides, it is considered being an important chapter in the subject, hence candidates must put equal effort into this chapter to raise their ranks. Also Check NEET Chemistry Syllabus
NEET, being a competitive exam, surely manages to ask most of the questions up to a considerable level. Also, when it comes to NEET, physics seems to be the toughest of all subjects. However, there are certain tricks you can follow to study for the examination in a more efficient way, which we will be looking at later in this article.
Basic concepts of Dual Nature of Matter & Radiation
|An electromagnetic wave shows dual nature i.e., (wave-particle) nature.|
|When a matter is moving, it shows certain wave properties such as diffraction, interference, etc., and when it is at rest, it shows particle properties. This is known as the dual nature of matter.|
Wave Nature of Matter
- As De Broglie proposed, the Wave Nature possesses a symmetry. He said if light and radiations display the characteristics of both wave and particle nature, the matter should also contain the wave-particle nature.
- According to De Broglie's hypothesis, the wavelength that is associated with the momentum is too small, this is the reason why microscopic elements don't show any characteristic of the wave nature.
- The relation between momentum and wavelength is given as , where p = momentum, h = Planck's constant, and l = wavelength. It is also called the De Broglie wavelength.
The wavelength for photon's
- De Broglie's concept of the dual nature of matter can further be demonstrated in quantitative measures.
- The energy of a photon possessing wavelength and frequency v is represented as: , where , i.e., .
The wavelength of an electron
- The de Broglie wavelength of an electron is represented as:
- Electrons of mass 'm' and de Broglie's wavelength fall on the target in an X-ray tube. The cut-off wavelength ( 0) of the emitted X-ray is -
- 0 = 2mc2 / h
- 0 = 2h / mc
- 0 = 2m2c23 / h2
- 0 =
Answer: A. 0 = 2mc2 / h
Cathode rays are beams of electrons that are emitted from a negatively charged electrode inside a discharge tube.
Properties of Cathode Rays
- Cathode rays travel in a straight line.
- They are emitted perpendicularly to the cathode
- They contain energy and momentum.
- Cathode rays affect the photographic plate.
- These rays get diverted by the electric and magnetic fields.
- Ionize gas
The electrons in the metallic surface are emitted through one of these emission processes:
- Thermionic Emission: In this method, the metallic surface is suitably heated using thermal energy until the electrons become able to escape the surface freely.
- Field Emission: Here, a very strong electric field is applied to the metal surface (of order 108 Vm-1) for the emission of electrons.
- Photoelectric Emission: When electromagnetic radiation (such as light) of a suitable frequency strikes the metallic surface and illuminates it for the emission of electrons, this process is called photoelectric emission.
- When light is incident on a metallic surface (cathode), the electrons on the surface acquire enough energy to get past the positive ions on the metal surface.
- Once these electrons obtain a substantial amount of energy to repel the attractive bond of the positive ions, the electrons escape from the surface to the surrounding.
- The electrons that are emitted when electromagnetic radiation hits a material are called photoelectrons.
- The photoelectric effect is an instantaneous process.
- For a photoelectric effect to take place, the frequency/ wavelength of the incident light ray must be greater than or at least equal to the work function.
- The relation between the energy and momentum of photons is mentioned below:
E = p × c, where p = magnitude of momentum and c = speed.
- The work function of metal can be defined as the minimum energy required by an electron to emit from that metal surface. The work function of a metallic surface is measured in eV (electron volt) and is denoted by W.
- 1eV = 1.602 × 10-19 J
Work Functions of Metals
|Metals||Work Function (in eV)|
The metal cesium has the lowest work function of 2.14 eV, while Platinum has the highest work function of 5.65 eV.
- It is the minimum frequency required for the emission of electrons from the metallic surface.
- It is denoted by v0.
- V0 = W/h
- The threshold frequency for the photoelectric effect for a surface is found to be 4.8 × 1016 Hz. The stopping potential required when the metal is eradicated by radiation of a frequency 5.6 × 1016 Hz is:
Einstein's Photoelectric Equation
here V0 = cut-off potential,
v0 = cut-off frequency or threshold frequency
v = frequency of incident (photon) light
Vmax = Maximum velocity obtained by photoelectrons
- What is the value of maximum kinetic energy acquired by electron due to radiation of a wavelength of 100 nm?
- 12 eV
- 6.2 eV
- 100 eV
- 300 eV
Answer: 6.2 eV
Relation between Potential and Photoelectric Current
- The photoelectric current increases uniformly with an increase in the accelerating potential.
- When the photoelectric current reaches its maximum, it is called the saturation current.
- When the photoelectrons acquire the saturation state, all photoelectrons get emitted from the emitter and reach the collector plate.
Relation between Intensity of the Incident Light and Photoelectric Current
- If the frequency of the incident radiation or light is below the minimum frequency of the metal surface, photocurrent doesn't take place. It decreases rapidly and finally becomes zero, which is also called the cut-off frequency or the stopping potential of the metal plate.
- This cut-off frequency or the stopping potential for the photoelectric current is basically a physical property of the metal plate.
- If the stopping potential is adequate enough to push back even the high-energy photoelectric particles approaching with the maximum kinetic energy, only then the photocurrent becomes zero or reach the cut-off frequency.
- K(max) = eV0
NEET Dual Nature of Matter & Radiation - Important Formulas
The most important formulas from the chapter Dual Nature of Matter and Radiation for NEET exams are mentioned below. It appears that most of the questions asked during your NEET examinations are mostly based on the following formulas:
- Energy of Photon:
- Kinetic mass of Photon:
- Momentum of Photon:
- De Broglie's wavelength equation:
- Work Function:
- Einstein's Photoelectric equation:
Important Tips To Solve Your Paper
While appearing for your physics paper in the NEET 2021, try to follow the following tips to complete your paper efficiently within the remaining time.
- Since your physics paper will be set in a certain order of difficulty, it will contain easy, moderate, lengthy, and twisty questions. Start with the simple ones and complete them at your fastest pace to save time to appear for the lengthy and twisty ones.
- While solving the paper, if you come across a lengthy question in middle, note the question number in your mind and move to the next easy or moderate level question.
- Suppose the answers for your MCQ's contains numbers such as 12, 2.7, 4.8, -7, avoid the extreme numbers 12 and -7 and look if your answer lies in the remaining two options. If not, only then move to the extreme values. This is because, in the previous year's NEET papers, it is found the answers to such questions mostly lie in the moderate values. Only rare questions satisfy the extreme ones.
- Avoid guess works as much as possible to lose marks from negative marking.
Monthly Study Plan for NEET Physics
Before you start studying to complete the physics syllabus for your NEET exams, it is good practice to make a precise plan based on the chapter weightage in the exams and come up with a weekly/ monthly study plan. For example, you can refer to the information below and come up with your own study schedule as per your time availability and preferences.
Physics Chapter-wise weightage for your NEET Exams 2021
|Unit||Weightage in NEET 2021
|Heat & Thermodynamics||9|
|SHM & Waves||7|
Step-wise plan for preparation for your Physics paper in NEET 2021
- The first step before truly starting your preparation is to analyze the exam pattern and the marking scheme in the examination.
- Next, by looking at the weightage each unit carries, start with the one containing the maximum weightage, in this case, it is the mechanics unit.
- Complete all the chapters in each unit accordingly, clear your concepts, and practice as many numerical as you can.
- After completing your regular textbooks, refer to the best reference books for practicing more complex numerical and revise the concepts.
- Try to appear for multiple online mock tests before sitting in the final exam. This will bring more efficiency to your problem-solving skill and you can develop proper time management.
- Lastly, work on your weakest concepts to build a strong foundation before sitting in the exam.
- Revise the concepts and practice more numerical problems.
- Solve last year's question papers.
- Avoid learning a new topic at the last minute. This might effect the concepts you have previously learned and you might end up mixing things up.
- Be calm, confident, and maintain a positive attitude.
- Stay fit and healthy.
Previous Year Solved Sample Questions
Ques: The light of frequency is 1.9 times the threshold frequency and is also incident on a photosensitive material. If we half the frequency and double the intensity then photocurrent becomes
Answer: (d) zero
Ques: For a metal having a work function W0, the threshold wavelength is λ. So if the metal having work function 2W0 then what would be the threshold wavelength?
Answer: (b) λ/2
Ques: How to determine the maximum velocity of the electron reacting with the collector in photoelectric effect?
- Incident radiation frequency
- Difference between the emitter & collector
- The work function of metal
- All of theseAnswer:
Answer: (d) All of these
Ques: Who established that electric charge is quantized?
- R.A. Millikan
- Wilhelm Rontgen
- William Crookes
- J.J. Thomson
Answer: (a) R.A. Millikan
Ques: If 2 lines i.e. A & B, in the plot shows the variation of de-Broglie wavelength, λ versus 1V√, Where V is the accelerating potential difference, for two particles carrying the same charge. Which one of two represents a particle of smaller mass?