Electric Circuits

Student Learning Objectives
Lessons / Lecture Notes
Important Equations
Example Problems
Applets and Animations

Student Learning Objectives

• To understand how current flows through conductors.
• To understand and apply a basic model for current, including conservation of current.
• To introduce resistivity, resistance and Ohm's law.
• To develop and use a conceptual model of simple DC circuits.
• To understand how a battery creates a current in a circuit.
• To understand series and parallel resistances.
• To draw and interpret basic circuit diagrams.
• To understand energy transfer and power dissipation and circuits.
• To understand how and why circuits are grounded.

Lessons / Lecture Notes

The Physics Classroom (conceptual)

PY106 Notes from Boston University (algebra-based):

Introductory physics notes from University of Winnipeg (algebra-based):

HyperPhysics (calculus-based)

PHY2049 notes from Florida Atlantic University (calculus-based):

PHY2044 notes from Florida Atlantic University (calculus-based)

General Physics II notes from ETSU (calculus-based)

Important Equations

Example Problems

Problem 1
(a) When a potential difference of 12 V is applied to a wire of radius 0.33 mm and length 6.9 m, the result is an electric current of 2.1 A. What is the resistivity of the wire? (Solutions)

(b) The resistance of a bagel toaster is 12.5 Ω. To prepare a bagel, the toaster is operated for one minute from a 120-V outlet. What is the current through the toaster? How much energy is delivered to the toaster? (Solutions)

Problem 2
A circuit containing six resistors is connected to a 120 V power supply as shown in the figure below. (a) What is the equivalent resistance of the six resistors? (b) How much charge flows through the power supply in 2.5 minutes? (c) What is the potential difference between points A and B? (Solutions)

Applets and Animations

 Circuit / Water Analogy A simple DC circuit has a DC voltage source lighting a light bulb. Also shown is a hydraulic system in which water drives a turbine. The two systems are shown to be similar. Battery Voltage Look inside a battery to see how it works. Select the battery voltage and little stick figures move charges from one end of the battery to the other. A voltmeter tells you the resulting battery voltage. Battery Resistor Circuit Look inside a resistor to see how it works. Increase the battery voltage to make more electrons flow though the resistor. Increase the resistance to block the flow of electrons. Watch the current and resistor temperature change. Ohm's Law See how the equation form of Ohm's law relates to a simple circuit. Adjust the voltage and resistance, and see the current change according to Ohm's law. The sizes of the symbols in the equation change to match the circuit diagram. Resistance in a Wire Learn about the physics of resistance in a wire. Change its resistivity, length, and area to see how they affect the wire's resistance. The sizes of the symbols in the equation change along with the diagram of a wire. Signal Circuit Why do the lights turn on in a room as soon as you flip a switch? Flip the switch and electrons slowly creep along a wire. The light turns on when the signal reaches it. Light Switch A simple animation of how a common light Switch works. Circuit Construction Kit (DC) An electronics kit in your computer! Build circuits with resistors, light bulbs, batteries, and switches. Take measurements with the realistic ammeter and voltmeter. View the circuit as a schematic diagram, or switch to a life-like view. Combinations of Resistors This applets allows the user to create series and parallel combinations of resistors and measure the resulting current. Simple Buzzer A simple buzzer consisting of a battery, a flexibile metal strip, a piece of iron, and some wire. Charging and Discharging a Capacitor This applets shows an animation of a capacitor that is charging or discharging. Use the mouse cursor to control the Switch Position slider, and discover how a capacitor is charged and discharged with current from the battery. Lightning - a Natural Capacitor This applets shows an animation of how lightning is formed and explains how lightning is an example of a natural capacitor. RC Circuit This applet allows the user to set the resistance and capacitance of a simple RC Circuit. The applet plots the voltage across the capacitor and the current in the circuit. RC Circuit RC Circuit models the dynamical behavior of a voltage source attached in series to a resistor and capacitor. The source voltage can be chosen to be either a 10 volt sinusoidal or square wave with an adjustable frequency.