![]() I hope this was helpful let me know if you have any other questions. This gives rise to the idea that perhaps light is not continuous but comes in photons, or discrete quanta of energy that directly interact with individual particles, like electrons.Īt the time, many physicists were content with the classical mechanics view of light as continuous waves that can't be broken down into discrete blocks, but this experiment proved otherwise - giving experimental evidence towards the quantum mechanics view of light and shaking up the world of physics along the way (Einstein even won a Nobel Prize for this). And indeed, this is what happened experimentally by using a much less intense light of a much higher frequency, photoelectrons were finally detected. Instead, by increasing the energy of each "individual" light or photon by increasing the frequency (think Planck's Equation, E=hv), that's like pressing the button hard enough to finally activate whatever it does - this is analogous to finally ejecting the photoelectron. If this concept is hard to understand, think of it like this: if you tried to partially press a button thousands of times, you might use up a lot of energy on your end, but the button would never carry out its function. It makes sense now that even by adding more of these "weaker" waves, none of the electrons would be ejected. However, experimental evidence shows that you can keep increasing the intensity of the light, but photoelectrons will still not be detected because metal surface's electrons will not be ejected.īut let's say we think of the light not as a continuous wave but more as a lot of individual, discrete packets of electromagnetic waves (aka photons). In fact, this is what the classical mechanic view of electromagnetic waves says should happen. However, if your light doesn't have enough energy to excite a second, different type of metal, it stands to reason that if you increased the amount of light, you would be adding more energy and thus be able to eject photoelectrons. This is known as the photoelectric effect. If the energy of the light is high enough to excite the electrons, electrons will be ejected (these electrons are known as photoelectrons) from the metal if the light's energy is high enough. The photoelectric effect experiment went like this: Take a metal surface, and shine a light on it. Because of this, the particle (photon) model of light was developed (where light is composed of discrete particles of energy) and the concept of wave-particle duality soon followed. However, increasing the frequency to certain points (depending on the type of metal being studied) did eject electrons, even if the intensity of light was very low. Under the wave model of light, a higher amplitude (intensity) would cause the light wave to have greater energy and thus be able to eject electrons, but this was experimentally not the case. What was so surprising about the photoelectric experiment was that if light of a certain frequency did not eject electrons from the sample, no amount of increasing the light's intensity would cause electrons to be ejected. Wavelength and frequency do not depend on intensity, and intensity does not depend on wavelength/frequency. ![]() Intensity is separate from these, as it has to do with the amplitude of the wave (under the wave model) or the number of photons transmitted (under the particle model). If wavelength increases, then frequency decreases and vice versa. Clearly, the larger the strength of the electric and magnetic fields, the more work they can do and the greater the energy the electromagnetic wave carries.Ī wave’s energy is proportional to its amplitude squared ( circuit containing a 1.00-pF capacitor oscillates at such a frequency that it radiates at a 300-nm wavelength.Wavelength and frequency have an inverse relationship, as indicated by the equation. If absorbed, the field strengths are diminished and anything left travels on. This is described by the Fresnel equations: R k i tan( t) tan( i + t) 2 (6) R i sin( t. ![]() Once created, the fields carry energy away from a source. When linearly polarized light is incident on a plane surface, the amount of light reected, the reectance (R), depends on the angle of incidence and the orientation of the polarization vector relative to the scattering plane. With electromagnetic waves, larger E-fields and B-fields exert larger forces and can do more work.īut there is energy in an electromagnetic wave, whether it is absorbed or not. Energy carried by a wave is proportional to its amplitude squared. This simultaneous sharing of wave and particle properties for all submicroscopic entities is one of the great symmetries in nature. These particle characteristics will be used to explain more of the properties of the electromagnetic spectrum and to introduce the formal study of modern physics.Īnother startling discovery of modern physics is that particles, such as electrons and protons, exhibit wave characteristics. But we shall find in later modules that at high frequencies, electromagnetic radiation also exhibits particle characteristics. The behavior of electromagnetic radiation clearly exhibits wave characteristics.
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