Optics & Modern Physics
Ray optics, wave optics, photoelectric effect, atomic models, and nuclear physics
Key Concepts
- Snell's law governs refraction; total internal reflection occurs beyond the critical angle
- Mirror and lens formula share the same sign convention
- Young's double slit produces interference fringes
- Photoelectric effect: electrons are ejected only above the threshold frequency
- Bohr model: energy is quantised as E_n = −13.6/n² eV
Important Formulae
| Mirror / lens formula | 1/f = 1/v − 1/u |
| Snell's law | n₁ sinθ₁ = n₂ sinθ₂ |
| Lens maker's formula | 1/f = (n−1)(1/R₁ − 1/R₂) |
| Fringe width (YDSE) | β = λD/d |
| Photoelectric effect | KE_max = hf − φ |
| Radioactive half-life | t₁/₂ = 0.693/λ |
Quick Tips
- Power of a lens P = 1/f (in metres), measured in dioptres; lenses in contact add.
- Bright fringe when path difference = nλ; dark when (2n−1)λ/2.
- Mass defect × c² gives the nuclear binding energy.
Sample Practice Questions
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The power of a lens of focal length 0.5 m is:
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Answer: 2 D
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In Young's double-slit experiment, increasing the slit separation d causes the fringe width to:
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Answer: Decrease
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Total internal reflection can occur only when light travels from a:
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Answer: Denser to a rarer medium
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The lens formula is:
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Answer: 1/f = 1/v − 1/u
Practice Questions
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What are the key concepts in Optics & Modern Physics for JEE?
Snell's law governs refraction; total internal reflection occurs beyond the critical angle; Mirror and lens formula share the same sign convention; Young's double slit produces interference fringes; Photoelectric effect: electrons are ejected only above the threshold frequency; Bohr model: energy is quantised as E_n = −13.6/n² eV.
Which formulae are important for Optics & Modern Physics in JEE?
Mirror / lens formula: 1/f = 1/v − 1/u; Snell's law: n₁ sinθ₁ = n₂ sinθ₂; Lens maker's formula: 1/f = (n−1)(1/R₁ − 1/R₂); Fringe width (YDSE): β = λD/d; Photoelectric effect: KE_max = hf − φ; Radioactive half-life: t₁/₂ = 0.693/λ.
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