Lesson: Circuits Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

Keywords:  capacitor, circuit, coulomb, current, e lectrical, electricity, electronic, energ y, inductor, Ohm's law, power, resistance, resistor, volt, voltage capacitorcircuitcoulombcurrente lectricalelectricityelectronicenerg yinductorOhm's lawpowerresistance resistorvoltvoltage

Learning Objectives  Define electric current and voltage.  Explain the relationship between voltage, current and resistance (Ohm's law).  List several different circuit components.

Pre-Lesson Assessment  What things do you use every day that have electric circuits?

Lesson

Thinking  Do you know why a cell phone must have a battery or why a computer must be plugged in to work?  (Answer: Those devices need electricity to work.)

Open vs Closed Circuits  Did you know that a battery or the power coming from the outlet in the wall is part of an electrical circuit?  When a battery is placed in the cell phone or when a computer is plugged in, the circuit in the device is completed or "closed," allowing electric current to flow.

Types of Engineers  Electrical Engineers: are most commonly associated with the development of circuits, but they are not the only engineers who work with and know about circuits. Most engineers must understand electricity and the physics behind circuits so they can design any devices that use electricity.

 Mechanical engineers, for example, use circuits when designing motors.  Aerospace engineers use circuits when designing controls for spacecraft.

What’s in a Circuit?  Resistors  Capacitors  Transistors  Integrated Circuit  Inductors

Resistor  resistors (any two terminal objects that provide a voltage drop in order to oppose the flow of current through it)

Capacitor  capacitors (stores energy in an electric field),

Transistor  transistors (commonly used as an amplifier or a switch)

Inductor  inductors (stores energy inside of an electric field)

Integrated Circuit  An integrated circuit is one that has been designed to perform a given task and is often made up of several other components such as resistors, capacitors, inductors and transistors.

Electric Current

Unit of Current is Ampere (A) /Amp  Currents found in household devices are generally around 1 amp. However in electronic devices such as stereos and computers, the current is often on the scale of milliamps (1mA = A) or microamps (1μA = A).

Two types: Alternating & Direct  Alternating current comes out of your typical wall sockets in homes, schools and businesses. It is called "alternating" because the direction of the current is constantly changing.

Alternating vs Direct

Alternating Current  In the US, the alternating current from wall sockets is at 60 Hz (Hertz). This means that the current is changing directions 60 times every second.  60 Hz (Hertz) = 60 times every second

Direct Current  Direct current is the current produced by batteries. It always travels in one direction. Current is important because the moving charges carry energy and have a potential to do work.

Voltage  Voltage = Electric Potential = The pressure that forces electricity through wire.  The unit for voltage is the volt (V).  AA, AAA, C, and D batteries are all 1.5v  Car batteries are 12v  Lawn mower batteries are 6v  Motorcycle batteries are 6v or 12v  Smoke detectors use 9v batteries

Ohm’s Law V=IxR  Ohm's law states that the voltage across a resistor is proportional to the current flowing through the resistor.

In equation form, it looks like this:  V = I x R  V = Voltage (volts) V  I – Current (amps) A  R = Resistance (Ohms) Ω  10V = 2A x 5 Ω

Lesson Summary Assessment  What happens to I if you increase V?  What happens to I if R increases?