Modern Physics for NEET 2025: Photoelectric Effect & Dual Nature Explained

Modern Physics is one of the highest ROI chapters in NEET Physics. With 2–3 direct questions almost every year, it is considered one of the most scoring areas, especially for students who are clear with formulas and fundamental concepts.

The core topics under Modern Physics include:

Photoelectric Effect
Dual Nature of Matter and Radiation
Einstein’s Equation
de Broglie’s Hypothesis
Basic numericals involving stopping potential, work function, and particle wavelength

These topics are directly picked from NCERT and require minimum memorization beyond the standard formulas.

In this blog, you’ll find:

Key concepts and explanations
Must-know formulas
Previous year NEET questions
Practice questions with detailed solutions

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Modern Physics in NEET: Chapter Weightage & Trends

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Weightage:

Modern Physics consistently contributes 2–3 questions every year, which equals around 8–12 marks—with minimal calculation and maximum conceptual recall.

NEET Trends (2020–2024):

Year	Questions Asked	Topics Covered
2020	3	Photoelectric effect, Stopping potential
2021	2	de Broglie wavelength, Photon energy
2022	2	Threshold frequency, Work function
2023	3	K.E. of electrons, Planck’s constant
2024	2	Dual nature MCQ, Equation-based question

NEET Style:

Mostly NCERT-based theory or direct formula applications
Requires strong grip on units, constants, and dimensional accuracy
Commonly tested with one-liner fact-based questions or short numerical setups

Photoelectric Effect: Concept & Equations

What Is the Photoelectric Effect?

The photoelectric effect refers to the emission of electrons from a metal surface when it is exposed to light of a certain frequency or higher.

Heinrich Hertz first observed this phenomenon.
It was later explained by Albert Einstein, who introduced the idea of photons (packets of energy).
This confirmed that light has particle-like behavior, especially at high frequencies.

Einstein’s Photoelectric Equation

$boldsymbol{text{K.E} = hf - phi = frac{1}{2}mv^2}$

Where:

$boldsymbol{h}$ = Planck’s constant
$boldsymbol{f}$ = Frequency of incident light
$boldsymbol{phi}$ = Work function of the metal
$boldsymbol{text{K.E}}$ = Kinetic energy of emitted electron

This equation explains how a photon transfers its energy:

A portion goes into removing the electron (work function)
The rest becomes the kinetic energy of the ejected electron

NEET Applications:

Calculating threshold frequency (f₀): $boldsymbol{phi = h f_0}$
Finding stopping potential (V₀) using: $boldsymbol{eV_0 = h f - phi}$
Determining maximum K.E. of emitted electrons
Conceptual questions on intensity vs energy of light

Learn more with NEET Mock Test

Dual Nature of Matter & Radiation

de Broglie Wavelength Formula

According to Louis de Broglie, matter like electrons and protons also behave like waves, especially at atomic scales.

$boldsymbol{lambda = frac{h}{mv} = frac{h}{p}}$

Where:

$boldsymbol{lambda}$ = de Broglie wavelength
$boldsymbol{h}$ = Planck’s constant
$boldsymbol{m}$ = mass of the particle
$boldsymbol{v}$ = velocity of the particle
$boldsymbol{p}$ = momentum

This dual behavior explains:

Electron diffraction
Wave-like interference of particles
Why particles behave like waves at the quantum level

NEET Applications:

Questions involving moving electrons, protons, or neutrons
Comparing wavelength with mass or velocity
Conceptual MCQs: “Which has a shorter de Broglie wavelength?”

Key Formulas to Remember

Here’s a quick reference table of all the key formulas from Modern Physics that are frequently used in NEET:

Concept	Formula
Photoelectric Equation	$boldsymbol{text{K.E} = hf - phi}$
Energy of Photon	$boldsymbol{E = hf = frac{hc}{lambda}}$
de Broglie Wavelength	$boldsymbol{lambda = frac{h}{mv} = frac{h}{p}}$
Stopping Potential	$boldsymbol{eV_0 = hf - phi}$
Work Function / Threshold freq	$boldsymbol{phi = hf_0}$

Tip: NEET MCQs often present values in eV, nm, or Joules—so make sure to remember:

$boldsymbol{h = 6.63 times 10^{-34} , text{Js}}$
$boldsymbol{c = 3 times 10^8 , text{m/s}}$
$boldsymbol{1 , text{eV} = 1.6 times 10^{-19} , text{J}}$

Previous Year NEET Questions: Modern Physics

These are actual NEET-style questions from recent papers, showcasing common patterns and direct formula applications.

Q1. NEET 2024:
A photon of energy 6 eV is incident on a metal surface with a work function of 2 eV. What is the kinetic energy of the emitted electron?

Answer:
$boldsymbol{text{K.E} = hf - phi = 6 - 2 = 4 , text{eV}}$

Q2. NEET 2023:
What is the de Broglie wavelength of a particle with mass $boldsymbol{1 times 10^{-27}}$ kg and velocity $boldsymbol{2 times 10^3}$ m/s?
(Use $boldsymbol{h = 6.63 times 10^{-34} , text{Js}}$ )

Answer:

$boldsymbol{lambda = frac{h}{mv} = frac{6.63 times 10^{-34}}{1 times 10^{-27} times 2 times 10^3} = 3.315 times 10^{-10} , text{m}}$

Q3. NEET 2022:
The threshold frequency for a metal is $boldsymbol{f_0 = 4 times 10^{14} , text{Hz}}$ . What is the work function? (Use $boldsymbol{h = 6.63 times 10^{-34} , text{Js}}$ )

Answer:
$boldsymbol{phi = h f_0 = 6.63 times 10^{-34} times 4 times 10^{14} = 2.652 times 10^{-19} , text{J}}$

In eV:
$boldsymbol{phi = frac{2.652 times 10^{-19}}{1.6 times 10^{-19}} = 1.66 , text{eV}}$

Q4. NEET 2021:
Which of the following quantities has the same dimensions as Planck’s constant hhh?
A) Energy
B) Momentum
C) Angular momentum
D) Force

Answer:
Planck’s constant has units of angular momentum.

$boldsymbol{[h] = [M L^2 T^{-1}]}$

Correct option: C

Practice Questions: Modern Physics

Q1. Light of wavelength 400 nm falls on a metal with work function 2.2 eV. Find the stopping potential.

$boldsymbol{h = 6.63 times 10^{-34} , text{Js}}, quad boldsymbol{c = 3 times 10^8 , text{m/s}}, quad boldsymbol{1, text{eV} = 1.6 times 10^{-19} , text{J}}$

Solution:

$boldsymbol{E = frac{hc}{lambda} = frac{6.63 times 10^{-34} times 3 times 10^8}{400 times 10^{-9}} = 4.97 times 10^{-19} , text{J}}$

In eV:
$boldsymbol{E = frac{4.97 times 10^{-19}}{1.6 times 10^{-19}} approx 3.1 , text{eV}}$

Q2. Which photon has more energy: UV light with 200 nm wavelength or IR light with 800 nm?

Solution:

$boldsymbol{E = frac{hc}{lambda}}$ ,Shorter $boldsymbol{E = frac{hc}{lambda}}$ , $boldsymbol{text{Shorter } lambda Rightarrow text{Higher } E}$

So, UV photons have more energy than IR.
Answer: UV light.

Q3. If the kinetic energy of an electron is doubled, what happens to its de Broglie wavelength?

Solution:

$boldsymbol{lambda = frac{h}{sqrt{2mK}}, quad lambda propto frac{1}{sqrt{K}}}$

$boldsymbol{K rightarrow 2K}, quad boldsymbol{lambda' = frac{lambda}{sqrt{2}}}$

So the wavelength decreases by a factor of 2sqrt{2}2

Q4. What is the momentum of a photon of wavelength 500 nm?

Solution:

$boldsymbol{p = frac{h}{lambda} = frac{6.63 times 10^{-34}}{500 times 10^{-9}} = 1.326 times 10^{-27} , text{kg·m/s}}$

Q5. A metal has a threshold wavelength of 600 nm. Will light of 450 nm cause photoemission?

Solution:
Yes. Since 450 nm < 600 nm, it has higher energy than threshold.
Answer: Yes, photoemission will occur.

FAQs on Modern Physics for NEET

Is Modern Physics difficult for NEET?

Not at all. It’s one of the easiest and most scoring chapters. All you need is clarity on concepts and formulas like Einstein’s equation and de Broglie wavelength.

Are there derivations in NEET from this chapter?

No. NEET never asks for derivations. It tests your understanding of concepts and ability to apply standard formulas to simple situations.

How many questions come from Modern Physics?

Usually 2–3 questions every year—making this a high-weightage, low-effort chapter to prepare.

Which books are best to prepare for this chapter?

NCERT Physics (Class 12 Part 2) – Must read
MTG 33 Years NEET PYQs
DC Pandey (Objective Physics) – for practice questions

Check out our NEET Residential Coaching option for focused preparation.

Conclusion

Modern Physics is a formula-first and concept-driven chapter that rewards smart preparation. With just 4–5 formulas and basic logic, you can confidently solve all NEET questions from this unit.

To master this chapter: