13 Electric Circuits

Chapter Outline 1 Electric Circuits and Electric Current 2 Ohm’s Law and Resistance 3 Series and Parallel Circuits 4 Electric Energy and Power 5 Alternating currents and Household Current Everyday Phenomenon: The Hidden Switch in Your Toaster

Use of Voltmeter Voltmeter is connected across the resistance.

Ammeter is inserted into the circuit to measure current. Use of Ammeter Ammeter is inserted into the circuit to measure current.

Electrical Energy

Electrical Energy and Power Our daily life depends on electrical energy. We use many electrical devices that transform electrical energy into other forms of energy. For example, a light bulb transforms electrical energy into light and heat. Electrical devices have various power requirements. Electrical power, P is defined as the electrical energy transfer per unit time,

Electric Power: Since the electrical energy is charge times voltage (QV), the above equation becomes, Since the current is charge flow per unit time (Q/t), the above equation becomes, Since V = IR, the above equation can also be written as,

Killowatt-hour (kWh) The SI unit of power is watt, after James Watt (1736-1819), who developed steam engines. Utility companies use the unit kilowatt-hour to measure the electrical energy used by customers. One kilowatt-hour, kWh is the energy consumed for one hour at a power rate of 1 kW.

Exercises 1. State Ohm’s law in an equation form in terms of voltage and current. 2. Define power in an equation form in terms of voltage and current. 3. When an appliance is plugged in a 120-volt outlet, it draws a current of 8 amperes. Calculate the power of the appliance. 4. If the above appliance is used 10 hours a day for 28 days per month, and if the cost of electricity is 12 cents per kilowatt‑hour, how much does it cost to operate the appliance for a year?

Electrical Power Transmission

AC adapter                        INPUT: AC 120 V, 60 Hz, 15 W OUTPUT: DC 9V, 1A

Alternating Current

Alternating Voltage Effective voltage = 115 V

Household Circuits

Power and Current Ratings of some common Appliances Power (W) Current (A) Stove 6000 (220V) 27 Clothes dryer 5400 (220V) 25 Water heater 4500 (220V) 20 Clothes washer 1200 10 Dishwasher Iron 1100 9 Coffeemaker 1000 8 TV 100 0.8

Everyday Phenomenon

Bimetallic Thermostat

CP5