The Photoelectric Effect: How Digital Cameras Work

This article explains the photoelectric effect and how digital cameras work.

The photoelectric effect is the name given to the property of some metals that allows them to emit electrons when light is shone on their surfaces. When a photon with a certain amount of energy strikes a particular atom, that atom absorbs the photon as energy. This energy is usually stored in the atom’s electron cloud, and when too much energy is accumulated, an electron can fly out of its orbit and become a free electron. This only happens when a photon of sufficient energy strikes the surface, because photons without enough energy to cause an electron to be emitted will simply be reflected.

Another interesting, and highly useful property of the photoelectric effect is that photo surfaces can discriminate based on the energy of photons. This is useful because the energy of a given photon determines its frequency, or what color it will appear as to the human eye. This means that a small photo surface will emit energy directly proportional to the intensity of the color of light that it was designed to measure. This allows for precise readings of the energy levels of light, and is responsible for a breakthrough in studying the light patterns of stellar objects.

Digital cameras are perhaps the most natural result of the discovery of the photoelectric effect. A camera works by measuring data from thousands of tiny pixels, which are squares of four photo surfaces designed to measure the red green and blue light values used by computers. In order to allow thousands of pixels to feed information to a computer, capacitors are attached to each pixel. Capacitors allow for the storage of electrical energy for a predetermined period of time. Modern capacitors are able to take in a charge and re-emit the charge from the other end of the capacitor after lengths of time that are specific enough to transmit a constant stream of data from a camera’s photo surfaces to a computer, where the signal is converted to a binary representation of the image.

This technology allows us to capture highly detailed digital images in short amounts of time. Instead of using film to capture data, digital storage has revolutionized image capture technology, using the simple principles of the photoelectric effect. In addition to cameras, similar technology is used in LCD screens, where the photoelectric effect can work in reverse, allowing pixels to emit light, rather than reading it from an outside source.

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Posted on Jul 8, 2010
Dr. Johnson C Philip
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Posted on Apr 17, 2010