How do Antenae pickup electromagnetic waves?

[SASQUATCH]

How do antenna (radio) and retina cells (visible light) pickup the particular em Wavelengths that they do?

What does the turning a radio knob translates has (does it alter the antenna or what)?

Is there any relationship between the antenna’s size and the length of the wavelength it can pick up? (Or transmit?)

Discuss.

[Grimmy]

Turning the knob on a radio changes the frequency in which the radio will recieve, or filter out the unwanted frequencies. I know in AM it changes what we called in college the "pocket" that carries the info. With FM it's totally different. You have resonant frequencies, which can carry elevator music, but requires a special filter to tune it in.

Longer the antenna, the further you can get out, along with more power. I believe the type of antenna determines the wavelength (like AM vs FM).

[SASQUATCH]

Antennae and retinas work by entirely different principles.

Radio waves that stike antennae cause electrons to surge back and forth, as determined by the frequency of the EMR. Most of the energy is reflected or re-radiated back into space. The antenna is attached to a tuning circuit that lets a few specific wavelengths pass through to the rest of the radio circuitry.

The tuning devices allow various frequencies to pass through and to block the rest. They typically work by altering the capacitance of a resonant circuit.

Yes, the antenna's size, configuration, and position have a tremendous effect on its effectiveness at receiving various wavelengths.

The retinal cells work on a different principle. They use photochemical reactions. Light of the proper frequency alters the chemical structure of the cells' components. The reactions are reversible. The new structures, when formed, transmit an impulse along the optic nerve to the brain. The various photochemical in the eye react only to EMR in the visible spectrum.

Cheers Grim and good to hear from you.