Physics, 20.08.2019 22:30 bhaven2005

The excitation of an electron on the surface of a photocell required 5.0 x 10 –27 j of energy. calculate the wavelength of light that was needed to excite the electron in an atom on the photocell

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C = speed of light in vacuum = about 3 x 10⁸ meters/second
h = Planck's Konstant = 6.63 x 10⁻ ³⁴ joule-second

Energy = (h x frequency) = (h c / wavelength)
Wavelength = (h c) / (energy)

Wavelength = (6.63 x 10^-34 joule-sec x 3 x 10^8 meter/sec) / (5 x 10^-27 joule)

= 19.89 x 10^-26 / 5 x 10^-27 = 39.78 meters

This is an astonishing result ! Simply amazing. That wavelength corresponds
to a frequency of about 7.54 MHz, in one of the short-wave radio bands used by
a lot of foreign-broadcast stations.

If the number in the problem is correct, it means that this 'photocell' responds
to any electromagnetic signal at 7.54 MHz or above ... short-wave radio,
commercial FM or TV signals, FRS walkie-talkies, garage-door openers,
Bluetooth thingies, home WiFi boxes, WiFi from a laptop, microwave ovens,
cellphones, any signal from a satellite, any microwave dish, any heat lamp,
flashlight, LED, black light, or X-ray machine. Some "photocell" !

I'm thinking the number given in the problem for the energy of a photon
at the detection threshold of this device must be wrong by several orders
of magnitude.

(But my math is still bullet-proof.)

Answer from: Quest

answer; (arch); good luck

Answer from: Quest

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia

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The excitation of an electron on the surface of a photocell required 5.0 x 10 –27 j of energy. calcu...

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