What is Waves and light: Definition and 29 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. Danielk010

    How does one calculate the number of photons striking a surface per second?

    I am more so stuck on where to start with this problem. I know dividing the photons per second by the area gets me the photon per area, but I am not sure how the distance is related to this part of the problem. If anyone can help, thank you.
  2. deuteron

    I Physical Meaning of the Imaginary Part of a Wave Function

    We know the wave function: $$ \frac {\partial^2\psi}{\partial t^2}=\frac {\partial^2\psi}{\partial x^2}v^2,$$ where the function ##\psi(x,t)=A\ e^{i(kx-\omega t)}## satisfies the wave function and is used to describe plane waves, which can be written as: $$ \psi(x,t)=A\ [\cos(kx-\omega...
  3. Ahmed1029

    I What Determines the Speed and Clarity of Signals in Wave Physics?

    What exactly is a signal in wave physics? Is any wave considered a signal? Like, consider a superposition of harmonic plane waves, is the signals it carries considered the envelope(that travels at the group velocity) or the individual rippes that travel at a the phase velocity?
  4. 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?
  5. 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...
  6. 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.
  7. 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.
  8. L

    Multiple-Choice Questions on the Behaviour of Waves and Light 😁

    Question 1; The conditions for total internal reflection are: -That light is traveling from an optically denser medium (higher refractive index) to an optically less dense medium (lower refractive index) - That the angle of incidence is greater than the critical angle. Therefore, I conclude that...
  9. E

    State three reasons why the phase difference between two light waves

    what would cause the phase difference ?
  10. A

    Understanding Polarization-Dependent Phase Shifts of Radio Waves

    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...
  11. 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...
  12. 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 traveled 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)...
  13. 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...
  14. Samuel Williams

    How Do Stokes Parameters Relate to Polarized Light Components?

    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...
  15. 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) ##...
  16. shihab-kol

    Can the Doppler Effect Cause Changes in Radio Wave Frequency?

    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...
  17. 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)...
  18. 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...
  19. M

    How does a light wave change when travelling from water to air?

    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...
  20. 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...
  21. 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...
  22. C

    Conceptual help: matter waves and light waves

    Ok so I'm coming to terms with the following: 1 - Matter is not a wave, nor does it propagate as a wave. There is no physical wave, amplitude, etc. The probability of the position of matter varies in a wave-like pattern. It is often called a wave because physicists have no explanation for why...
  23. L

    Solving for Nodal Lines in a Two Point Source Interference Pattern

    Homework Statement A two point source interference pattern is generated in a ripple tank by identical sources vibrating in phae and located 12.0cm apart. there are seven nodal lines observed on each side of the centre line. if the wavelength of the sources is doubled and they remain in phase...
  24. L

    Waves and light (problem solving)

    Homework Statement two speakers producing exactly the same frequency and always in phase are located on an east-west line emitting sound toward the north. the speakers are 30cm apart and a microphone is loacted 40cm due north of one speaker. which of the following wavelengths would produce...
  25. N

    Do sound waves and light rays interact?

    Homework Statement see topic title Homework Equations I think that sound waves are vibrations of particles in a medium. The vibrations continue until the energy is gone. Sound seems to need a medium to travel through. Light can travel in a vacuum. your eye sees it from a source...
  26. Y

    Questions about waves and light

    I have a few questions: 1. Most CD players use laser light in the red portion of the spectrum. What changes would be required in the manufacturing of CDs if blue light were to be used? 2. A student performs Young's double-slit experiment using a slit separation of 21.6um. A screen is...
  27. J

    Waves and light (conceptual questions)

    [SOLVED] waves and light (conceptual questions) hey, i have a few conceptual questions related to waves and light. 1. what is the ratio of thickness of crown glass and water that would contain the same number of wavelength of light? (index of refraction for glass = 1.52, and for water, it's...
  28. R

    Understanding the Relationship of n=Sine i/Sin r for Waves and Light Homework

    Homework Statement http://img103.imageshack.us/img103/7336/12345va5.png The Attempt at a Solution n= Sine i/Sin r n= Sin 3o/Sin15 n=1.93 Is That Right
  29. R

    Calculating Average Distance Between Bright Fringes in a Double-Slit Experiment

    1. A double-slit experiment is performed using a monochromatic light source, two slits spaced 0.10 mm apart, and a screen located 150 cm away. The bright fringes are located 0.30 cm apart. If the screen distance was changed to 3.0 m from the sources, what would the average distance between...
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