Bell Ringer: Define to the best of your ability the definition of: Electric Circuit Current Voltage Resistance Resistor Coulomb Ampere

(Pun Intended) Notes 8.2: Current Electricity This lesson brought to you by the shockingly Brilliant Mr. Jenkins!

Learning on Your Own: (1) Active Physics -        Chapter 5, Section 1, Page 600  - Generating Electricity        Chapter 5, Section 2, Page 609 - A Model for an Electrical Circuit        Chapter 5, Section 4, Page 625 - Ohm's Law: Putting up a Resistance        Chapter 5, Section 5, Page 633 - Electrical Power  (2) Physics (Red Book) – Chapter 22, Page 590 – Current Electricity Instructional Videos Online: https://www.youtube.com/watch?v=8RJ6Kdk8KDo

Lesson Objective: Describe conditions that create current in an electric circuit. Understand the energy flow and power within a circuit. Design basic closed circuits. Define current. Define Resistance. Understand what effects the resistance of an object. Explain Ohm’s Law Recognize common symbols used in explaining circuits.

Electric Circuit: An electric circuit is any closed loop or conducting path allowing electric charges to flow. Electrical circuits have batteries, resistors, and wires. The battery provides the voltage source to the circuit. Recall that voltage is the energy (in joules) for each coulomb of charge. A resistor can be thought of as a light bulb or something of the sort. We will get into resistors more in a moment.

Electric Current: The battery in a circuit provides the energy for each coulomb of electrical charge that will move in a circuit. The rate of flow of an electrical charge is the CURRENT. Current: the rate of flow of electric charge; the number of coulombs passing a point in one second. 𝑖= 𝑞 𝑡

Electric Current: 𝐼= 𝑞 𝑡 I = current q = charge t = time SI Unit of Current: ampere A = 1 Coulomb/second NOTE: Often we shorthand ampere and just call it an amp or amps.

Rates of Charge Flow and Energy Transfer: Recall what is Power. Power measures the rate at which energy is transferred or P = E/t If the energy in a circuit is E = qV, then P = qV/t; and if I = q/t, then we can determine that the rate at which energy is transferred in a circuit is: 𝑃=𝐼𝑉 P = Power I = Current V = Voltage

Example I: A 6.0 V battery delivers a 0.50 A current to an electric motor connecta cross its terminals. a. What power is delivered to the motor? b. If the motor runs for 5.0 min, how much energy is delivered?

How is current (I) related to charge (q), directly or inverse? Check-Point I: How is current (I) related to charge (q), directly or inverse? If you increase the current, what happens to the Power in the circuit? What is the current through a 75 W lightbulb that is connected to an outlet that is 125 V? A car battery causes a current of 2.0 A through a lamp and produces 12V across it. What is the power used by the lamp? 1) Directly 2) The Power will increase. 3) 0.6 C 4) 24 W

What happens when you plug in a glass rod between the two wires? Resistance: What happens if you connect two wires to a battery and then plug in a copper rod in between the two wires? What happens when you plug in a glass rod between the two wires? What happens with you plug in a piece of rubber in between them? For one thing, you will notice that the flow of electricity is goes through each item differently. 1) Directly 2) The Power will increase. 3) 0.6 C 4) 24 W

Resistance is the hindrance of to the flow of charge. Everything has a resistance. For something’s you would want a low resistance so that the electricity is conducted through easily. That filament in your light bulb is a resistor. Does a light bulb have high or low resistance? A resistor is device designed to have a specific resistance. 1) Directly 2) The Power will increase. 3) 0.6 C 4) 24 W

1) Directly 2) The Power will increase. 3) 0.6 C 4) 24 W

Resistance & Ohm’s Law: Ohm’s Law states that the electric current flowing through a metallic wire is directly proportion to the potential difference across its ends, provided its temperature remains the same. 𝑅= 𝑉 𝐼 R = resistance V = voltage I = current SI Unit for Resistance = Ohms  Ω=𝑉/𝐴

Power and Resistance: Previously we saw that P = IV. Well now we know that V = IR, so we can relate the two equations to attain some more equations for Power. 𝑃= 𝐼 2 𝑅 𝑃= 𝑉 2 𝑅 P = Power (in watts W) I = Current (in amps A) V = Voltage (in volts V) R = Resistance (in ohms Ω)

Resistance & Ohm’s Law: You have a 12 V battery with a 3 Ω resistor (light bulb). What is the measured current with in the circuit?

Check Point II: Define Resistance. List two factors that affects the resistance of an object. What is the SI Unit of Resistance. A 2Ω resistor is placed in a circuit. Record the currents corresponding to voltage measurement of 30 V.

Diagramming Circuits:

Exit Ticket: What is an electric circuit? Define current. Define resistance. A 75 W lamp is connected to 125 V battery. (a) What is the current through the lamp? (b) What is the resistance of the lamp?