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6 public questions tagged with this topic.

Applications of EM Waves in Communication and Medicine

Which frequency range corresponds to short wave bands used in radio communication?

**Microwaves in ovens** cause water molecules to rotate at 2.45 GHz, friction heats food, penetration depth few cm, efficient heating, also radar uses reflection of microwaves from objects, Doppler shift measures speed, medical diathermy uses microwaves for tissue heating. The document states that frequencies up to 54 MHz are used for short wave bands in radio communication. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Up to 54 MHz, illustrating EM wave transverse nature and Maxwell's displacement current concept.

Ref: NCERT > Physics Book > Electromagnetic Waves > Applications of EM Waves in Communication and Medicine

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Energy, Intensity and Momentum of EM Waves

What is one technological importance of electromagnetic waves mentioned in the document?

**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 highlights that electromagnetic waves can carry energy, enabling technologies like radio and TV signals for broadcasting. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields They carry energy for communication, illustrating EM wave transverse nature and Ma

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

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Electromagnetic Spectrum - Radio Waves and Microwaves

What characteristic of radio waves enables their use in broadcasting over large areas?

**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. Radio waves have long wavelengths, allowing them to diffract around obstacles and reflect off the ionosphere, facilitating wide-area coverage for broadcasting. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Long wavelength, illustrating EM wave transve

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

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Electromagnetic Spectrum - Radio Waves and Microwaves

What is the approximate wavelength range of radio waves as per the document?

**Hertz experiment** produced radio waves using spark gap LC oscillator, detected with loop antenna, confirming Maxwell's prediction, frequency ≈10⁸ Hz, wavelength ≈3 m, demonstrating EM waves travel at c, transverse, can be reflected, refracted, polarized. The document states that radio waves have wavelengths greater than 0.1 m , with long radio waves up to 10⁶ m . Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields > 0.1 m, illustrating EM wave transverse nature and Maxwell's displacement current concept.

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

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Sexual selection

Honest signals must be:

Costly reflects key principle in quiz on sexual selection + pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Costly aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Costly fits helps integrate natural selection, environment.

Ref: Andersson, Sexual Selection, Princeton, Mate Choice and Good Genes.

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Cancer

Cancer cells communicate with stroma primarily by

Secreting signaling proteins and proteases, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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