# lecture15 - Electrical Work and Power Text sections 27.6...

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Electrical Work and Power Electrical Work and Power Text sections 27.6, 28.1 •Electrical work and power •“emf” Practice problems: 27-37, 27-43, 28-3 Electrical Work and Power Electrical Work and Power I I +- V 1 V 2 Resistance R Current I flows through a potential difference V Follow a charge Q : at positive end, U 1 = QV 1 at negative end, 2 = 2 P.E. Decreases: V Q U = Î Electrical energy is converted to other forms of energy.

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Questions: 1) If potential energy is lost, is the kinetic energy of the electrons increasing? 2) If the charge carriers are negative instead of positive, will the potential energy increase with time? Power: Power: P = work per unit time V I t V Q P = = Power = current x (potential difference) Units: 1 volt x 1 amp = 1 watt (= 1 J/s) Eg. Resistor: V = IR Î P = I 2 R (rate of “Joule heating” in resistor)
Examples Examples 1) What is the resistance of a “60 watt” bulb? (for a 120-V supply) 2) Find R for a 60-W headlamp (12-V battery).

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lecture15 - Electrical Work and Power Text sections 27.6...

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