Chapter 20 - Electricity Section 20.2 (Electric Currents) Section 20.3 (Electric Circuits)
Flow of a Charge • An electric current is a steady flow of electric charge. • Electric charges will flow continuously only through a closed conducting loop called a circuit.. circuit
How a Current Flows • A simple electric circuit contains a source of electrical energy, such as a battery battery,, and an electrical conductor, such as a wire wire.. • In the figure, a closed path is formed by wires connecting a lightbulb to a battery.
Voltage • In an electric circuit, a battery increases the electrical potential energy of electrons. • Voltage is a measure of how much electrical potential energy each electron can gain. • Voltage is measured in volts (v).
Batteries • Chemical reactions in batteries produce an electric field in batteries which cause electrons to move from the positive (+) to negative ((-) terminal. terminal. • Batteries contain only a limited amount of the chemicals needed to create this electric field. • When the battery runs out of the chemicals,, it is “dead”. chemicals
Resistance • The measure of how difficult it is for electrons to flow through a material is called resistance resistance.. • The unit for resistance is the ohm (Ω (Ω). • Insulators generally have much higher resistance than conductors conductors..
Ohm’s Law • Ohm’s Law states: • Voltage (V) = Current (Amps) * Resistance (Ω (Ω) • According to Ohm’s Law, when the voltage in a circuit increases the current increases increases.. • Example – Just as water flows faster from a bucket that is raised higher.
WHAT IS AN ELECTRICAL CIRCUIT? • Answer: – A closed path that allows an electrical current to flow from a power source (i.e., batteries). Electricity flows from the negative terminal to the positive terminal. – If there are any “breaks” in the loop, electricity will not flow! – There are two types of circuits we will build: 1. Series 2. Parallel
Series Circuits If all the parts of an electric current are connected one after another, the circuit is a series circuit. In a series circuit, there is only one path for the current to take.
Series Circuits - Demonstration Advantage – Very simple to design and build. Disadvantage – A burnedburned-out bulb is a break in the circuit, circuit, and there is no other path for the charges to take. Disadvantage – Light bulbs in the circuit added. become dimmer as more bulbs are added. Why? Bulbs add more resistance. Ohm’s Law – if resistance increases, current decreases.
Parallel Circuits In a parallel circuit, the different parts of the circuit are on separate branches. branches. In a parallel circuit, there are several paths for current to take.
Parallel Circuits - Demonstration Disadvantage – More complicated to design and build. Advantage – If one bulb goes out, the others remain lit. lit. Advantage – If more bulbs/branches are dimmer. added, the bulbs do not become dimmer. Why? More paths to take = less resistance = more current
Build a Series Circuit Using the two batteries and three bulbs at your station, build a Series Circuit with the people at your lab station. Take turns building the circuit. circuit.
Build a Parallel Circuit Using the two batteries and three bulbs at your station, build a Parallel Circuit with the people at your lab station. Take turns building the circuit.
