Quantities of a Circuit

The 3 Quantities of a Circuit

• In any circuit, Voltage, Current, and Resistance are all interconnected– Change one, change them all

Ohm’s Law

• As voltage increases, so does the current• If resistance increases, the current decreases

I = V R

Current (amps)

Voltage (volts)

Resistance (ohms)

Voltage

• Related to potential energy (stored energy)– Differences in electrical energy pushes electrons

through circuit– We measure it in volts

• Ex) Batteries

How Batteries Work

• Inside battery are chemicals that separate (+) & (-) charges

• When wires are connected, the charge flows from (+) to (-) and neutralize battery

• Most batteries are 1.5 V batteries– The positive end of a battery is 1.5 V higher than

the negative end

Types of Batteries

• D-cell, AA, AAA– Lettered batteries (AAA, AA, C, D) have the same

volts (1.5 V)– Difference is in how long they’ll last– Bigger they are (D), the longer they’ll last

• Batteries can be paired together to create a higher voltage

Current

• Amount of electricity flowing• More current there is, more electricity flowing• Current carries energy AND does work

Current

• Measured in amps (A)• Circuit breakers in house regulate the amount

of current flowing through the wires– Using too many appliances on a single circuit can

cause an excessive amount of current to flow– If too much current is flowing through the wires,

they can get very hot and possibly start a fire– The circuit breaker is designed to trip before that

happens• A fuse does the same thing, however circuit

breakers can be reset, fuses must be replaced

Types of Current

1. Alternating current (AC)– current that goes back and forth along the circuit– Ex) electricity in house or school– In the U.S., each wall socket has three wires that

carry 120 volts– When you plug something in, the current flows into

and out of the hot wire, through your appliance and out through the neutral wire

– A third, ground wire is for safety. In case of a short circuit the current flows through this wire and not you• Used around water sources

2. Direct Current (DC)– This current only goes one direction– Ex) Batteries

Resistance

• refers to how easily charges flow through an object– measured in ohms (Ω)– The higher the resistance, the more difficult it is

for current to flow

Electrical Conductivity

• property of a material to allow charges to flow– Things with high conductivity are generally

conductors– Conductivity changes from material to material

Conductors

• Most wires are made of copper since allows charges to flow through very easily

• Most metals are good conductors

Semiconductors

• Some materials with properties of both– The invention of semiconductors allowed for the

technology that we all can’t live without today (like computers)

– EX) Silicon

Insulators

• There are other materials block charges and block current– EX) Styrofoam, glass and plastic

Works Cited

• Hsu Ph.D., Tom. Foundations of Physical Science. 1st ed. Peabody: Cambridge Physics Outlet, 2002. 113-125. Print.

• Murray, Stephen. "Worksheets." Mr. Murray’s Science Website: IPC Worksheets. N.p., 2009. Web. 18 May 2012. http://www.cstephenmurray.com/Acrobatfiles/IPC/ch6to9/chap6no2.pdf