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#electromagnetic radiation

7 public questions tagged with this topic.

Polarization and Malus Law

What is the nature of light waves demonstrated by polarization?

**Two polaroids** with pass-axes perpendicular intensity zero because second blocks component, with 45° intensity I₀/4 if initial after first I₀, if initial unpolarized I₀, after first I₀/2 then after second at 45° I₀/4. Three polaroids first and third crossed 90°, middle at 45° maximum transmission because middle rotates polarization, I after first I₀/2, after middle at 45° I₀/4, after third at 45° to middle I₀/4×cos²45°= I₀/8, non-zero, maximum when middle 45°. Polarization shows that light waves are transverse, as only transverse waves can be polarized. Using Δ = d sinθ, y = n λ D/d, a sinθ

Ref: NCERT > Physics Book > Wave Optics > Polarization and Malus Law

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Energy, Intensity and Momentum of EM Waves

Which type of electromagnetic waves are produced by bombarding a metal target with high-energy electrons?

**Energy in EM wave** equally divided between electric and magnetic fields, energy density u = ½ ε₀ E² + B²/(2μ₀) = ε₀ E² = B²/μ₀, average u_avg = ½ ε₀ E₀², intensity I = c u_avg = ½ c ε₀ E₀² = E₀ B₀/(2μ₀) = c B₀²/(2μ₀), radiation pressure p = I/c for absorption, 2I/c for reflection. The document states that X-rays are generated by bombarding a metal target with high-energy electrons. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields X-rays, illustrating EM wave transverse nature and Maxwell's displacement current concept.

Ref: NCERT > Physics Book > Electromagnetic Waves > Energy, Intensity and Momentum of EM Waves

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Infrared, Visible Light and Applications

What is a common method to detect visible light according to the document?

**Visible light** λ≈400-700 nm, f≈4×10¹⁴ to 7×10¹⁴ Hz, narrow part of spectrum sensitive to human eye, produced by atomic transitions, used for vision, photosynthesis, optical fibers, central frequency ≈5×10¹⁴ Hz, different colors correspond to different λ. The document lists the human eye, photocells, and photographic film as detectors of visible light. Photocells are a common method in devices. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Photocells, illustrating EM wave transverse nature and Maxwell's displacement current concept.

Ref: NCERT > Physics Book > Electromagnetic Waves > Infrared, Visible Light and Applications

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EM Wave Characteristics - Transverse Nature and E/B Ratio

In the context of electromagnetic waves, why do oscillating charges act as effective sources?

**Relationship E and B** in EM wave E₀ = c B₀, B₀ = E₀/c, for vacuum. Fields sustain each other via Maxwell's equations ∇×E = -∂B/∂t, ∇×B = μ₀ ε₀ ∂E/∂t, time-varying E produces B and vice versa, self-sustaining propagation without medium, speed c. Oscillating charges undergo acceleration, producing time-varying electric fields that induce magnetic fields, which sustain each other to form propagating electromagnetic waves. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields They produce time-varying fields, illustrating EM wave transverse nature and

Ref: NCERT > Physics Book > Electromagnetic Waves > EM Wave Characteristics - Transverse Nature and E/B Ratio

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Electromagnetic Spectrum - Radio Waves and Microwaves

Why are microwaves used in domestic microwave ovens?

**Microwaves** λ≈10⁻³ to 0.3 m, f≈10⁹ to 10¹² Hz, produced by klystron/magnetron, used in microwave ovens because frequency ≈2.45 GHz matches rotational resonance of water molecules, causing dielectric heating, also radar, satellite communication due to small wavelength allows directional beams. The document explains that microwaves are used because their frequency matches the resonant frequency of water molecules, efficiently transferring energy to heat food. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Their frequency matches water molecul

Ref: NCERT > Physics Book > Electromagnetic Waves > Electromagnetic Spectrum - Radio Waves and Microwaves

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NMRSpectroscopy

What type of radiation is used in NMR spectroscopy?

NMR relies on Zeeman splitting of nuclear spin levels, creating energy gaps in radiofrequency range, typically tens to hundreds of megahertz for common magnets. Irradiating sample with radio waves at Larmor frequency induces transitions between spin states when resonance condition matches. Unlike X-rays that ionize molecules or infrared that excites vibrations, radiofrequency is low-energy, non-ionizing, non-destructive, allowing repeated measurements of living cells and proteins. This gentle nature enables dynamic studies of protein folding, ligand binding, and metabolic flux without damaging

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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