A lithium battery used in a cardiac pacemaker has a voltage of 3.0 V and a capacity of 0.50 A h (ampere hour). Assume that 5.0 μW of power is needed to regulate the heartbeat. Appendix B.

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Current electricity is a flow of electrically charged particles. In electric currents in metallic conductors, the charged particles are electrons; in molten salts or in aqueous solutions, the particles are both negatively and positively charged ions. As pointed out in Section B-5, the unit of electric charge is called a coulomb (C). The unit of electric current known as the ampere (A) is defined as a flow of one coulomb per second through an electrical conductor. Two variables determine the magnitude of the electric current I flowing through a conductor. These are the potential difference, or voltage drop, E, along the conductor, and the electri- cal resistance of the conductor, R. The units of voltage and resistance are the volt (V) and ohm, respectively. The relationship of electric current, voltage, and resistance is given by Ohm's law. E R (B.15) One joule of energy is associated with the passage of one coulomb of elec- tric charge through a potential difference (voltage) of one volt. That is, one joule = one volt-coulomb. Electric power refers to the rate of production (or consumption) of electric energy. It has the unit watt (W). 1 W = 1Js¹ - 1 VCs-¹ Since one coulomb per second is a current of one ampere, 1 W = 1V X 1 A (B.16) Thus, a 100-watt light bulb operating at 110 V draws a current of 100 W/110 V = 0.91 A.