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  2. Light - Wikipedia

    en.wikipedia.org/wiki/Light

    For example, the speed of light in water is about 3/4 of that in vacuum. ... The weakness of the wave theory was that light waves, like sound waves, would need a ...

  3. Electromagnetic spectrum - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_spectrum

    Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin. In a later experiment, Hertz similarly produced and measured the properties of microwaves.

  4. Visible spectrum - Wikipedia

    en.wikipedia.org/wiki/Visible_spectrum

    An example of this phenomenon is when clean air scatters blue light more than red light, and so the midday sky appears blue (apart from the area around the Sun which appears white because the light is not scattered as much). The optical window is also referred to as the "visible window" because it overlaps the human visible response spectrum.

  5. Electromagnetic radiation - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_radiation

    As a wave, light is characterized by a velocity (the speed of light), wavelength, and frequency. As particles, light is a stream of photons. Each has an energy related to the frequency of the wave given by Planck's relation E = hf, where E is the energy of the photon, h is the Planck constant, 6.626 × 10 −34 J·s, and f is the frequency of ...

  6. Spectrum (physical sciences) - Wikipedia

    en.wikipedia.org/wiki/Spectrum_(physical_sciences)

    The classical example of a continuous spectrum, from which the name is derived, is the part of the spectrum of the light emitted by excited atoms of hydrogen that is due to free electrons becoming bound to a hydrogen ion and emitting photons, which are smoothly spread over a wide range of wavelengths, in contrast to the discrete lines due to ...

  7. List of light sources - Wikipedia

    en.wikipedia.org/wiki/List_of_light_sources

    This is a list of sources of light, the visible part of the electromagnetic spectrum.Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic energy, and include light bulbs and stars like the Sun. Reflectors (such as the moon, cat's eyes, and mirrors) do not actually produce the light that ...

  8. Absorption (electromagnetic radiation) - Wikipedia

    en.wikipedia.org/wiki/Absorption_(electromagnetic...

    This example shows the general principle using visible light as a specific example. A white light source—emitting light of multiple wavelengths—is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines). Upon striking the sample, photons that match the energy gap of the molecules present (green light ...

  9. Polarization (waves) - Wikipedia

    en.wikipedia.org/wiki/Polarization_(waves)

    Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, [6] and transverse sound waves (shear waves) in solids. An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular to each other. Different ...