Please, someone tell me...

Why is it that when I put my hand next to the volume knob on my amp the right speaker kicks in, and when I take it away the speaker cuts out again?
Why is it that when I hold my radio it gets perfect reception and when I take my hand away the reception deteriorates?
Why is it that when I walk under the street light outside my house it turns on, then flickers and turns off when I walk away?

What is the relationship between human presence and the function of electronics?