Voltage and Current

• Electrical potential energy is the ability to move an electric charge from one point to another.
• The electrical potential energy of the moving charge decreases because the electric field does work on the charge.
• The electrical potential energy depends on the distance between two charged objects for both an attractive and a repulsive electric force.
• Potential difference is measured in volts.
• The potential difference between any two points, is the work that must be done against electric forces to move a unit charge from one point to the other.
• The volt, V, is equivalent to one joule per coulomb (1 J/C).
• Potential difference is often called voltage.
• There is a voltage across the terminals of a battery.
• A cell isa device that is a source of electric current because of a potential difference, or voltage, between the terminals.
• One terminal is positive, and the other is negative.
• Batteries convert chemical energy into electrical energy.
• A voltage sets charges in motion.
• Current (I) is the rate that electric charges move through a conductor.
• The SI unit of current is the ampere, A.
• 1 amp = 1 C/s
• A battery is a direct current source because the charges always move from one terminal to the other in the same direction.
• Conventional current is defined as movement of positive charge.
• The direction of current in a wire is opposite the direction that electrons move in that wire.

Electrical Resistance

• Resistance is the opposition posed by a material or a device to the flow of current.
• Resistance is caused by internal friction, which slows the movement of charges through a conducting material.

Resistance can be calculated from current and voltage

Resistance = voltage/current ( r = v/I )

• The SI unit of resistance is the ohm, Ω. 1 Ω = 1 V/A
• A resistor is a special type of conductor used to control current.
• Conductors have low resistances.
• Some materials become superconductors below a certain temperature.
• Certain metals and compounds have zero resistance when their temperature falls below a certain temperature called the critical temperature.
• Semiconductors are intermediate to conductors and insulators.

The controlled addition of specific atoms of other materials as impurities dramatically increases a semiconductor’s ability to conduct electric charge.