Electricity!!!

http://www.jimsdestinations.com/elebas3.htm

http://kids.discovery.com/tell-me/curiosity-corner/science/how-do-electric-circuits-work

http://www.hantsfire.gov.uk/circuits

http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/electric_current_voltage/revision/4/