2 Chapter Outline 1 Electric Circuits and Electric Current 2 Ohm’s Law and Resistance3 Series and Parallel Circuits4 Electric Energy and Power5 Alternating currents and Household CurrentEveryday Phenomenon:The Hidden Switch in Your Toaster
3 Use of VoltmeterVoltmeter is connected across the resistance.
4 Ammeter is inserted into the circuit to measure current. Use of AmmeterAmmeter is inserted into the circuit to measure current.
6 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,
7 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,
8 Killowatt-hour (kWh)The SI unit of power is watt, after James Watt ( ), 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.
9 Exercises1. 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?
15 Power and Current Ratings of some common Appliances Power (W)Current (A)Stove6000 (220V)27Clothes dryer5400 (220V)25Water heater4500 (220V)20Clothes washer120010DishwasherIron11009Coffeemaker10008TV1000.8