In a normal conductor heat is generated at a rate I 2R.Therefore a current-carrying conductor must dissipateheat effectively or it can melt or overheat thedevice in which it is used. Consider a long cylindricalcopper wire (resistivity 1.72 108 # m) of diameter0.75 mm. If the wire can dissipate 80 W/m2 along itssurface, what is the maximum current this wire cancarry?
Goals • To understand capacitors and calculate capacitance • To analyze networks of capacitors • To calculate the energy stored in a capacitor • To examine dielectrics and how they affect capacitance Introduction • How does a camera’s flash unit store energy • Capacitors are devices that store electric potential energy. • The energy of a capacitor is actually stored in the electric field. Capacitors and capacitance • Capacitors are devices that store electric potential energy. • The energy of a capacitor is actually stored in the electric field. • Any two conductors separated by an insulator form a capacitor • The definition of capacitance is C = Q/V . ab Parallel-plate capacitor • A parallel-plate capacitor consists of two parallel conducting plates separated by a distance that is small compared to their dimensions. • The capacitance of a parallel-plate capacitor is C = A/d. 0 Copyright © 2012 Pearson Education Inc. Other shapes of capacitors A spherical capacitor A cylindrical capacitor Capacitors in series • Capacitors are in series if they are connected one after the other • The equivalent capacitance of a series combination is given by 1/C =eq/C + 1/1 + 1/C 2 … 3 Copyright © 2012 Pearson Education Inc. Capacitors in parallel • Capacitors are connected in parallel between a and b if the potential difference V is abe same for all the capacitors. • The equivalent capacitance of a parallel combinat