In one general aspect, various embodiments are directed to a surgical instrument that can supply mechanical energy and electrical energy to an end effector of the surgical instrument. The surgical instrument may be operated in a first operating mode in which a transducer of the surgical instrument produces mechanical energy, or vibrations, that are transmitted to the end effector and a second operating mode in which electrical energy, or current, can flow through the end effector to perform electrosurgery. In another general aspect, the surgical instrument may comprise a clamp, or jaw, which can be moved into a closed position to hold tissue against a waveguide, or blade, of the end effector. In the second operating mode of the surgical instrument, current can flow from a power source, through the waveguide, and return to the power source through a path comprising the jaw.