How many basic energy sources are described as detaching electrons from atoms to sustain current?

• A. Five
• B. Six
• C. Seven
• D. Eight

Answer: (B)

When current is sustained by electrons leaving atoms, the energy source must be able to liberate those electrons. There are six basic energy forms described that can do this: chemical energy, light energy, thermal energy, mechanical energy, nuclear energy, and electrical energy. Each one can overcome the binding of outer electrons and release them so they can move as current. Chemical energy does this in batteries through redox reactions; light energy does it via photons in photoemission or solar cells; thermal energy causes thermionic emission from hot filaments; mechanical energy from friction or contact (triboelectric effect) can eject electrons; nuclear energy from radiation can ionize atoms and free electrons; electrical energy, through strong electric fields, can pull electrons off surfaces (field emission) or cause a spark discharge. Since these six distinct energy inputs are described as capable of detaching electrons to sustain current, the correct count is six.