Unit 4 – Electricity & Magnetism

Electricity & Its Production In this chapter we will explore; The quantities of electrical energy, power, electric current, potential difference, and resistance. Understand the movement of charge through a circuit. Describe properties of electric potential difference, current, and resistance for series, parallel, and mixed circuits. Analyze and solve problems in series, parallel, and mixed circuits.

11.1 Electrical Energy & Power Plants In physics, electricity refers to electrical energy and the movement of charge. The generation of electricity at power plants convert mechanical energy, thermal energy, and radiant energy into electrical energy. For example, in a hydroelectric power plant, kinetic energy from falling water is converted into electrical energy. Electrical devices in your home convert electrical energy into other forms of useful energy to perform particular tasks.

11.1 Electrical Power & Energy Recall in Section 5.5 that power (P) is the rate at which energy is transformed. Electrical power (P) is the rate at which electrical energy is produced, or consumed, in a given time, expressed in Watts (W). Electrical energy is measured in units of kilowatt hours (kWh) because the joule (J) is too small to be a convenient measurement. 1 kWh = 3.6 x 106 J. A typical home in Ontario uses 1000 kWh of electrical energy each month. When describing the electrical energy generated at a power plant, it is measured in megawatt hours (MWh). 1 MWh = 3.6 x 109 J; 1 MWh = 1000 kWh.

11.1 Efficiency of Power Plant Technologies

11.1 Homework Practice # 1, 2 p.505 Practice # 1, 2 p.506 Questions # 2-5 p.507

11.3 Electric Potential Difference Electrical energy is transferred from a power plant to your home through conducting wires called transmission lines. The wires are made of metal (aluminum), where electrons are free to move. This provides the means for the transfer of electrical energy. Negatively charged electrons repel one another. The closer electrons are pushed together, the greater the increase in their potential energy. Energy must be transferred to the electrons to overcome this repulsion; the movement in electrons requires a change in energy.

11.3 Electric Potential Difference Since electrons repel, the amount of energy needed to move a group of electrons closer together is the electric potential. The more work that is done to move them together, the higher the electric potential. A group of electrons is a quantity of charge (Q), measured in coulombs (C). Instead of measuring electric potential at one point in the circuit, it is more useful to measure the electric potential difference (V) between two points in a circuit, because energy is transformed in a circuit. Charge at the battery of a circuit has a different amount of potential than charge at a light bulb. SI units: ⤍ Joules per Coulomb of Charge (J/C) ⤍ Volt (V); 1 V = 1 J/C SP #1 p.511

11.3 Measuring Electric Potential Difference A voltmeter is an electrical device used to measure the electric potential difference in a circuit. Voltmeters only work accurately if a separate path is created in the circuit, which allows a small amount of electrons to go through the meter; In other words, the voltmeter must be connected in parallel. Circuits contain sources of electrical energy, such as a battery or a power supply, which cause an increase in electric potential (voltage gain). Loads, such as lamps, motors, and resistors cause a decrease in electric potential (voltage drop).

11.3 Homework Practice # 1 p.511 Questions # 1-6, 9 p.513

11.5 Electric Current The movement of electrons, or electric current, is required for an electric device to operate. Direct current (DC) is the flow of electrons in only one direction through a circuit. Electric current (I), is the rate of charge flow, measured in amperes (A). One coulomb of charge passing a point in a circuit every second is equivalent to one ampere. SI units: ⤍ Coulombs per second (J/s) ⤍ Ampere (A); 1 A = 1 C/s SP #1 p.516

11.3 Measuring Electric Current An ammeter is an electrical device used to measure the amount of electric current in a circuit. Ammeters must be connected in series so all electrons flowing through the circuit also flow through the meter. If the ammeter were connected in parallel, there would be more than one path for the current to flow through; not all of the current will flow through the ammeter, providing an inaccurate reading.

11.5 Homework Practice # 1, 2 p.517 Questions # 2-6 p.518