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meaning of transmission light waves
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Short answer
- "Transmission" of light waves means the portion of an incident electromagnetic wave that passes through a material or across an interface into another medium instead of being reflected or absorbed.
What physically happens
- At an interface between two media (for example air → glass) the incident light splits: some is reflected, some is transmitted. The transmitted wave continues into the second medium but generally with a changed direction, speed, wavelength and amplitude.
- Energy is conserved: reflectance R + transmittance T + absorptance A = 1 (for a given frequency and direction).
Key laws and formulas
- Snell’s law (direction change): n1 sin θ1 = n2 sin θ2, where n is refractive index and θ are angles measured from the normal.
- Fresnel relations (amplitudes at an interface): give reflection (r) and transmission (t) amplitude coefficients for perpendicular (s) and parallel (p) polarizations. Reflectance R = |r|^2. Transmittance for intensity must include refractive-index/angle factors, e.g.
T = (n2 cos θ2 / n1 cos θ1) |t|^2.
- Beer–Lambert law (bulk absorption): I(x) = I0 e^(−αx). Transmittance (through thickness x) = I/I0 = e^(−αx), where α is the absorption coefficient.
Other important points
- Amplitude vs intensity: amplitude coefficients (r, t) describe fields; intensities (R, T) are proportional to squared amplitudes and represent energy flow.
- Phase: the transmitted wave may acquire a phase shift that matters in interference and thin-film optics.
- Dispersion: wavelength in a medium λ = λ0/n, so transmitted light’s wavelength and speed change in the medium.
- Total internal reflection: when light goes from higher n to lower n beyond a critical angle, transmission into the second medium becomes zero (except evanescent fields).
Examples
- A glass window: transmits most visible light, reflects a small fraction, absorbs a little—so T is high but less than 1.
- Colored filters: transmit some wavelengths and absorb/reflect others; their transmission spectrum varies with wavelength.
- Optical fibre: light is confined by total internal reflection so little is transmitted out of the core.
If you want, I can:
- Derive the Fresnel coefficients,
- Show numeric examples of T and R for common materials,
- Explain transmission spectra and how to measure transmittance. Which would you like?
- "Transmission" of light waves means the portion of an incident electromagnetic wave that passes through a material or across an interface into another medium instead of being reflected or absorbed.
What physically happens
- At an interface between two media (for example air → glass) the incident light splits: some is reflected, some is transmitted. The transmitted wave continues into the second medium but generally with a changed direction, speed, wavelength and amplitude.
- Energy is conserved: reflectance R + transmittance T + absorptance A = 1 (for a given frequency and direction).
Key laws and formulas
- Snell’s law (direction change): n1 sin θ1 = n2 sin θ2, where n is refractive index and θ are angles measured from the normal.
- Fresnel relations (amplitudes at an interface): give reflection (r) and transmission (t) amplitude coefficients for perpendicular (s) and parallel (p) polarizations. Reflectance R = |r|^2. Transmittance for intensity must include refractive-index/angle factors, e.g.
T = (n2 cos θ2 / n1 cos θ1) |t|^2.
- Beer–Lambert law (bulk absorption): I(x) = I0 e^(−αx). Transmittance (through thickness x) = I/I0 = e^(−αx), where α is the absorption coefficient.
Other important points
- Amplitude vs intensity: amplitude coefficients (r, t) describe fields; intensities (R, T) are proportional to squared amplitudes and represent energy flow.
- Phase: the transmitted wave may acquire a phase shift that matters in interference and thin-film optics.
- Dispersion: wavelength in a medium λ = λ0/n, so transmitted light’s wavelength and speed change in the medium.
- Total internal reflection: when light goes from higher n to lower n beyond a critical angle, transmission into the second medium becomes zero (except evanescent fields).
Examples
- A glass window: transmits most visible light, reflects a small fraction, absorbs a little—so T is high but less than 1.
- Colored filters: transmit some wavelengths and absorb/reflect others; their transmission spectrum varies with wavelength.
- Optical fibre: light is confined by total internal reflection so little is transmitted out of the core.
If you want, I can:
- Derive the Fresnel coefficients,
- Show numeric examples of T and R for common materials,
- Explain transmission spectra and how to measure transmittance. Which would you like?
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