# 10.5 - Chapter 25 Electric Currents and Resistance Ccow-ght...

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Unformatted text preview: Chapter 25 Electric Currents and Resistance Ccow-ght «1 20L“.J Pomsm [ducallu IIIIII L. 25-2 Electric Current By convention, current is defined as flowing from + to -. Electrons actually flow in the opposite direction, but not all currents consist of electrons. meentionul Electron current ﬂow lilcclron currcnl C w titi‘ICICElPoatsan-ﬁllcannnIn: wcrhx! Sm( Maul \$6 915‘: 25-4 Resistivity For any given material, the resistivity increases with temperature: Pr — p.;.[l + «('1' * 1,311]. Semiconductors are complex materials, and may have resistivities that decrease with temperature. 25-3 Ohm’s Law: Resistance and Resistors In many conductors, the resistance is independent of the voltage; this relationship is called Ohm’s law. Materials that do not follow Ohm’s law are called nonohmic. Unit of resistance: the ohm, Q: 1 o = 1 WA. Consider two identical resistors wired in se- ries (one behind the other). If there is an electric current through the combination. the current in the second resistor is 1. equal to 2. half 3. smaller than, but not necessarily half the current through the ﬁrst resistor. 25-5 Electric Power What you pay for on your electric bill is not power, but energy - the power consumption multiplied by the time. We have been measuring energy in joules, but the electric company measures it in kilowatt-hours, kWh: 1 kWh = (1000 W)(3600 s) = 3.60 x 106 J. ...
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