Electric Current Chapter 17.2 Notes

Electrical Potential Energy Recall that gravitational potential energy depends on position—a ball at the top of a hill has greater gravitational potential energy than a ball at the bottom of a hill An electric charge also has electrical potential energy, or energy that depends on the position of the charge in an electric field For two charges of the same charge, the potential energy is greater when they are closer together; potential energy is smaller when the charges are farther apart

Electrical Potential Energy

Potential Difference Potential difference is the change in the electrical potential energy of a charged particle divided by its charge The change occurs as a charge moves from one place to another in an electric field The SI unit for potential difference is the volt (V), which is equal to one joule per coulomb (1 J/C) Potential difference is often just called voltage

Voltage Across a Battery The potential difference, or voltage, across the two ends, or terminals, of a battery ranges from about 1.5 V for a small battery to about 12 V for a car battery Most batteries are electrochemical cells—or groups of connected cells— that convert chemical energy into electrical energy

Moving Charges The connection between a positive and negative terminal will create a voltage; this voltage makes charges move from the side with a higher electrical potential energy to the side with a lower electrical potential energy The electric current is the rate at which the charges move through a wire The SI unit of current is the ampere (A) One ampere equals 1 coulomb of charge moving past a point in 1 second

Electrical Resistance Resistance is the opposition to current Resistance is caused by internal friction, which slows the movement of charges through a conducting material Resistance is found by dividing the voltage across a conductor by the current Ohm’s Law: resistance = voltage/current; R = V/I The SI unit of resistance is the ohm (Ω)

Resistance A resistor is a special type of conductor used to control current; every resistor has a specific resistance Whether or not charges move in a material depends on how tightly electrons are held in the atoms of the material Since electrons can flow easily through metal conductors, conductors have low resistance Insulators have a high resistance to charge movement; insulating materials are used to prevent electric current from flowing in undesired directions In semiconductors pure state, they are insulators

Superconductors Some metals and compounds have zero resistance when their temperature falls below a critical temperature—these materials are called superconductors The critical temperature depends on the material and ranges from less than -458 °F to as high as -198 °F Once a current is established in a superconductor, the current continues even if the applied voltage is removed