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Electric Power. Chapter 17 Lesson 4 p. 618. Source of Current: Potential Difference. If no potential difference: - Free electrons in a conductor move randomly when all points in the conductor are the same potential. If potential difference is applied:

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## Electric Power

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**Electric Power**Chapter 17 Lesson 4 p. 618**Source of Current: Potential Difference**• If no potential difference: - Free electrons in a conductor move randomly when all points in the conductor are the same potential. • If potential difference is applied: • Free electrons in a conductor move from a higher electric potential to a position of lower electric potential. * Potential difference maintains current in a circuit.**Batteries and generators supply energy to charge carriers.**• Battery – maintains a potential difference across its terminals by converting chemical energy to electric potential energy. • Generator – converts mechanical energy into electrical energy.**Current can be direct or alternating.**• There are two types of current: • Direct current (DC) – charges move in only one direction with negative charges moving from a lower to higher electric potential. - direction of current does not change • Alternating current (AC) – the terminals of the source of potential difference are constantly changing sign. - direction of current continually changes**Energy transfer**• A charge leaves the battery at A with a certain amount of electrical potential energy. The charge loses this energy while moving from B to C, and then regains the energy as it moves through the battery from D to A.**Electric Power is the rate of conversion of electrical**energy. Electric Power (P) is the rate at which charge carriers convert electrical potential energy to nonelectrical forms of energy. Electric Power = Current x Potential Difference Formulas: (1) (2) (3)**Practice E Problems**• A 1050 W electric toaster operates on a household circuit of 120 V. What is the resistance of the wire that makes up the heating element of the toaster? (#1, p. 621) 2. A calculator is rated at 0.10 W and has an internal resistance of 22 Ω. What battery potential difference is required for this device? (#3, p. 621)**Practice E Problems**3. An electric heater is operated by applying a potential difference of 50.0 V across a wire of total resistance 8.00 Ω. Find the current in the wire and the power rating of the heater. (#4, p.621) 4. The operating potential difference of a light bulb is 120 V. The power rating of the bulb is 75 W. Find the current in the bulb and the bulb’s resistance. (#56,Chapter Review,p. 628)**Electric Power**• The SI unit of power is the watt, W. • Electric companies measure energy consumed in kilowatt-hour. One kilowatt-hour (kW h) is the energy delivered in 1 h at the constant rate of kW. • Electrial energy is transferred at high potential differences to minimize energy loss.**Homework**1. A computer is connected across a 110 V power supply. The computer dissipates 130 W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the computer. (#55, Chapter Review, p. 628) 2. A small electronic device is rated at 0.25 W when connected to 120 V. What is the resistance of this device? (#2, Practice E, p. 621)

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