Chapter-13 Outline 1Electric Circuits and Electric Current, I 2 Ohm’s Law, V = I R; and Resistance, R. 3 Series and Parallel Circuits 4 Electric Energy and Power, P = IV 5 Alternating currents and Household Current

How to Get the Bulb to Light?

Electric Current The 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 André Ampére ( ). 1 A = 1 C/s. Ampere is a large unit for current. In practice milliampere (mA) and microampere (μA) are used.

Direction of Current Flow Electric 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.

Electromotive Force (emf) or Voltage 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) or simple the voltage, V of the battery. The SI unit for voltage is the volt, after Alessandro Volta ( ) who invented the electric battery. 1 volt = 1 J/C.

Electrical Resistance When electric current flows through a metal wire there exists a hindrance to the flow, known as electrical resistance. This is because as the electrons move through they will collide with the atoms of the conductor. The SI unit of resistance is the ohm (Ω), after Georg Simon Ohm ( ), a German physicist, who discovered Ohm’s law. A resistor is a material that provides a specified resistance in an electric circuit. Resistance is the primary component in many electrical devices. Examples: Toaster, Heater, Iron, incandescent light bulb, etc...

Electrical Quantities and their Units QuantitySymbolUnit Name Unit Abbreviation CurrentIampereA Voltage or emf VvoltV ResistanceRohmΩ PowerPwattW

Ohm’s Law Georg Simon Ohm ( ), a German physicist, discovered Ohm’s law in 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 ( ΔV) or voltage (V) created across the resistance. Ohm’s law gives a relationship between the potential difference (ΔV=V), current (I), and resistance (R) as follows: V = I R

What Is the Current?

Circuits

Series Circuit and Parallel Circuit

Use of Voltmeter and Ammeter Voltmeter 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 ( ), 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?

Electricity: Generation and Transmission electricity/nuclear.asp

Transformers A transformer consists of a primary coil and a secondary coil, both wound on an iron core. The changing magnetic flux produced by the current in the primary coil induces an emf in the secondary coil. At the far right is the symbol for a transformer. A transformer is a device for increasing or decreasing an ac voltage.

Power and Current Ratings of some common Appliances INPUT: AC 120 V, 60 Hz, 15 W OUTPUT: DC 9V, 1A AppliancePower (W)Current (A) Stove6000 (220V)27 Clothes dryer5400 (220V)25 Water heater4500 (220V)20 Clothes washer Dishwasher Iron11009 Coffeemaker10008 TV AC adapter

Alternating Current and Voltage Effective voltage = 115 V

Household Circuits SP5: 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?