Waves and light Definition and 17 Discussions

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).

The primary properties of visible light are intensity, propagation-direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature, as with all types of electromagnetic radiation (EMR), light is found in experimental conditions to always move at this speed in a vacuum.In physics, the term 'light' sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of electromagnetic radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed. The absorbed energy of the electromagnetic waves is called a photon and represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave instantly collapses to a single location and this location is where the photon "arrives". This is what is called the wave function collapse. This dual wave-like and particle-like nature of light is known as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics.
The main source of light on Earth is the Sun. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight.

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  1. samy4408

    B Question about electromagnetic waves -- Penetration vs. Frequency

    I read in a book that high frequency electromagnetic waves are more able to penetrate than low ones , so why radio waves can penetrate walls when light cannot?
  2. L

    Intensity of a laser beam at a certain distance

    I haven't been able to pinpoint a definition of "angular divergence" of a laser so by pure intuition I assumed it would be something like ##\theta=\frac{2R}{D}## and with that I have that the radius of the lase beam is ##R=\frac{D\theta}{2}=90\cdot 5 \cdot 10^{-6} m=450\ \mu m## so...
  3. jackiepollock

    Young's Double-Slit Experiment

    As I searched online an answer suggested that the blurry effect might be a speckle pattern. However, it still hasn't explained the reason why when my body come near the pattern gets blurry.
  4. O

    Angular Width Question in Single Slit Diffraction

    i feel like subbing the numbers into the equation isn't enough because of the second minima and maxima thing? not sure what to do... would appreciate any help.
  5. E

    State three reasons why the phase difference between two light waves

    what would cause the phase difference ?
  6. A

    Polarization dependent phase shift of EM waves on reflection off of a dense medium

    I've seen this video: There it is explained that an electromagnetic (here radio) wave has a phase shift if it was radiated in horizontal polarization, but it does not experience the phase shift when it was emitted vertically polarized when it gets reflected on the ground. When reading up on...
  7. J

    Destructive interference in Unpolarised light

    Destructive interference is excellently demonstrated in Young's double slit experiment, where dark regions are formed due the waves being out of phase. However, what really confuses me is that unpolarised light has intensity. Assuming we had perfectly unpolarised light, as in where the...
  8. TachyonLord

    Fizeau's Experiment (Speed of light)

    Homework Statement In the Fizeau's Experiment to determine the speed of light, let the gear have N teeth, the frequency of the rotating gear being f, the distance travelled by the light beam/ray L (distance b/w the gear and the mirror) and let there be n eclipses(blocking of the light beam)...
  9. P

    Why is there interference if EM waves don't interact?

    Radio waves pass through everywhere without interacting with each other and that enables us to hear different phone calls and radios without disturbance. However, we do hear some noise sometimes because different signals interfere with each other. How are both of the last two statements true (if...
  10. Samuel Williams

    Help with Stoke's Parameters

    Homework Statement Show that cos 2χ = ((Eb^2 - (Ea)^2) / ((Eb)^2 + (Ea)^2) = (-2(EL*ER)) / ((EL)^2 + (ER)^2) and sin 2χ = (2Ea*Eb) / ((Eb)^2 + (Ea)^2) = ((ER)^2 - (EL)^2) / ((EL)^2 + (ER)^2) where EL and ER are the left and right circularly polarized field components of a wave. Homework...
  11. PumpkinCougar95

    Confusion about the Energy Density of EM waves

    I am a bit confused about the energy density in an EM wave. why do we take the Peak value of E vector while calculating the energy density? Like if the E field is ##E_0 Sin(kx-wt)## what is the energy density of the EM wave(Magnetic + Electric)? is it A) ##\frac {e_0E_0^2}{2} ## or B) ##...
  12. shihab-kol

    Doppler Effect In Radio Waves

    I have learned that the Doppler effect causes a change in wavelength (and thus frequency) in all types of waves Suppose there is a radio station transmitting waves of frequency 90 kHz and the antennae in my car is tuned to that frequency. Then I start to accelerate and thus I am changing my...
  13. gsmtiger18

    Phase shift of light incident on 2 slits

    Homework Statement Light of wavelength λ = 450 nm is incident upon two thin slits that are separated by a distance d = 25 μm. The light hits a screen L = 2.5 m from the screen. It is observed that at a point y = 2.8 mm from the central maximum the intensity of the light is I = 55 W/m2. a)...
  14. A

    I How does a photon view the universe?

    This question has been bugging me quite some time now. I'll start presenting my background for the problem: Fact: Photons are time-dependent oscillations of electric and magnetic fields as described by Maxwell's equations. Now, I've heard a lot of people, including professors saying that a...
  15. M

    Final exam wave question

    I'm a high school physics teacher and this was a question posed to my Honors Physics class. [Simplified] A light wave travels from water to air. Which of the following variables does NOT change between the mediums?" A. speed B. wavelength C. amplitude D. frequency I intended the answer to be...
  16. abm77

    Waves -- Find the lowest possible values for m_r and m_v

    Homework Statement Two slits are separated by a distance of 4.40x10-6m and illuminated with two monochromatic light sources with wave lengths of 600nm (red) and 400nm (violet). The mr bright fringe of the red light coincides with the mv bright fringe of the violet light. What are the lowest...
  17. Z

    Destructive interference Sound question

    Homework Statement A student enters Best Buy prepared to buy a pair of speakers. Before he does so, he conducts an experiment with them. He places the speakers 4.0 m apart and connects a signal generator to both speakers that produces a single and consistent tone. (constant wavelength and...