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Here ya go. Red probe plugged into a single (hot) conductor of a 120VAC outlet, and black probe just stuck into the wet earth outside our house. You can read the meter voltage..

A variation on that experiment may also be instructional.. take a table lamp outside, and wire it with only one conductor going into the hot side of an outlet, and the other conductor stuck into the ground (do this with it switched OFF!!). Then turn on the switch, and watch what happens..

For an older home, the light will probably illuminate nice and bright.
With a newer home, probably nothing will happen.. can you guess why?