IIT JEE Physics Practice Paper – Modern Physics (Set 6)
Instructions
Total Questions: 20 | Marks: 4 each | No Negative Marking
Modern Physics – IIT JEE Notes (Set 6)
Photoelectric Effect
Concept
The photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency falls on it. It proves the particle nature of light.
Einstein Equation
hν = φ + KE(max)
Where h is Planck’s constant, ν is frequency, φ is work function, and KE is kinetic energy of emitted electrons.
Work Function and Threshold Frequency
Work Function
Minimum energy required to remove an electron from the surface of a metal.
Threshold Frequency
The minimum frequency required to initiate photoelectric emission. It depends only on the material.
de Broglie Hypothesis
Concept
Every moving particle has wave nature associated with it.
Formula
λ = h/p
Where λ is wavelength and p is momentum.
Photon and Energy Quantization
Photon Energy
E = hν
Key Insight
Energy of light is quantized and comes in discrete packets called photons.
Compton Effect
Concept
Scattering of X-rays by electrons leads to an increase in wavelength.
Importance
It confirms the particle nature of light and conservation of momentum.
Bohr Model of Atom
Postulates
Electrons revolve in fixed orbits with quantized energy levels.
Energy Levels
E ∝ -1/n²
Radius of Orbit
r ∝ n²
Atomic Spectra
Concept
When electrons transition between energy levels, they emit or absorb photons of specific wavelengths.
Key Insight
Each element has a unique spectral signature.
Nuclear Physics Basics
Nuclear Force
Short-range force that holds protons and neutrons together inside nucleus.
Binding Energy
Energy required to separate a nucleus into individual nucleons.
Radioactivity
Decay Law
N = N₀e^(-λt)
Half-Life
Time required for half of the radioactive substance to decay. It depends only on the nature of the nucleus.
Key Insight
Radioactive decay is random and unaffected by external conditions.
Mass-Energy Equivalence
Formula
E = mc²
Application
Used to explain nuclear reactions like fission and fusion.
Pair Production and Annihilation
Pair Production
A high-energy photon converts into an electron-positron pair in presence of a nucleus.
Annihilation
Electron and positron combine to produce energy in the form of photons.
Semiconductors
Types
Intrinsic and Extrinsic (n-type and p-type).
Key Insight
Conductivity increases with temperature, unlike metals.
Diodes and Transistors
Diode
Allows current to flow in one direction only.
Transistor
Used for amplification and switching in electronic circuits.
Important Exam Concepts
Conceptual Traps
Intensity affects number of electrons emitted, not their energy. Frequency controls energy in photoelectric effect.
JEE Strategy
Focus on formulas, graphs, and conceptual clarity. Practice numerical problems on photoelectric effect and radioactive decay.