# chapter-13 outline 1electric circuits and electric current, i 2 ohm’s law, δv = i r; and...

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Chapter-13 OutlineElectric Circuits and Electric Current, I 2 Ohms Law, V = I R; and Resistance, R.3 Series and Parallel Circuits4 Electric Energy and Power, 5 Alternating currents and Household Current

How to Get the Bulb to Light?

Electric CurrentThe electric current is the amount of charge per unit time that passes through a surface that is perpendicular to the motion of the charges.

The SI unit of electric current is the ampere (A), after the French mathematician Andr Ampre (1775-1836). 1 A = 1 C/s. Ampere is a large unit for current. In practice milliampere (mA) and microampere (A) are used.

Direction of Current FlowElectric current is a flow of electrons. In a circuit, electrons actually flow through the metal wires. Conventional electric current is defined using the flow of positive charges. It is customary to use a conventional current I in the opposite direction to the electron flow.

Electric Current Is Analogous to Water Flow

Electromotive Force (emf)

The energy needed to run electrical devices comes from batteries.Within a battery, a chemical reaction occurs that transfers electrons from one terminal (leaving it positively charged) to another terminal (leaving it negatively charged). Because of the positive and negative charges on the battery terminals, an electric potential difference exists between them. The maximum potential difference is called the electromotive force* (emf) of the battery.The electric potential difference is also known as the voltage, V.The SI unit for voltage is the volt, after Alessandro Volta (1745-1827) who invented the electric battery. 1 volt = 1 J/C.

Ohms LawGeorg Simon Ohm (1787-1854), a German physicist, discovered Ohms law in 1826. This is an experimental law, valid for both alternating current (ac) and direct current (dc) circuits.When you pass an electric current (I) through a resistance (R) there will be a potential difference or voltage (V) created across the resistance.Ohms law gives a relationship between the potential difference (V), current (I), and resistance (R) as follows:V = I R

What Is the Current?

Circuits

Series Circuit

Parallel Circuit

Example Box 13.2

Use of Voltmeter and AmmeterVoltmeter is connected across the resistance. 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.

Exercises1. State Ohms 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 kilowatthour, how much does it cost to operate the appliance for a year?

Electrical Power Transmission

Power and Current Ratings of some common AppliancesINPUT: AC 120 V, 60 Hz, 15 WOUTPUT: DC 9V, 1AAC adapter

AppliancePower (W)Current (A)Stove6000 (220V)27Clothes dryer5400 (220V)25Water heater4500 (220V)20Clothes washer120010Dishwasher120010Iron11009Coffeemaker10008TV1000.8

Alternating Current

Alternating VoltageEffective voltage = 115 V

Household CircuitsSP5: A 600-W toaster, a 1200-W iron, and a 500-W food processor are all connected to the same 115-V household circuit, fused at 15 A. a. What is the current drawn by each of these appliances? b. If these appliances are all turned on at the same time, will there be a problem. Explain. c. What is the resistance of the heating element in the iron?