Unit 3 Day 1: Voltage, Current, Resistance & Ohm’s Law Batteries Electric Current Conventional Current Resistance Resistors Energy Dissipated in a Resistor

Batteries Discovered by Luigi Galvani (1780) And improved upon by Alessandro Volta A battery produces electricity by transforming chemical energy into electrical energy, using various metal electrodes immersed in an electrolytic solution

Batteries Exterior to the battery, the electrodes are connected to terminals 2 or more batteries connected together in series ( + to – terminals) adds the voltage Batteries are the source of potential difference ΔV =V A-B & measured in SI units of volts (V)

Electric Current Electric current is the flow of electric charge in an electric circuit An electric circuit consists of a source of ΔV (battery), connecting wires, and a load (lamp)

Electric Current When a circuit forms a closed loop, conventional current flows out of the (+) terminal of the battery, into the load, and back into the (-) terminal of the battery

Electric Current Where ΔQ is the amount of charge that passes through a conductor at any location, during some interval of time. SI: Amperes (A) 1A = 1 Coulomb / sec Charge carriers are the electrons which flow out of the (-) terminal of the battery and into the (+) terminal

Electric Current Conventional current flows in the opposite direction of electron flow !

Electric Current + E-Field - - Current flows because the potential difference produced by the battery sets up an electric field parallel to the wires. Free electrons in the wire are attracted to the (+) end of the electric field There will be a continuous flow of electrons as long as ΔV is available

Resistance In 1850 Georg Simon Ohm determined that in a circuit,. The current is the circuit is limited or impeded by the amount of voltage applied to the circuit. This impediment to current flow is due to electrons colliding with metal atoms in the wire. This impediment to current flow is called resistance.

Resistance where R is the resistance, SI: Ohms (Ω) 1 Ω = 1 volt / ampere This is called Ohm’s Law

Resistors All electronic devices which represent a load in an electronic circuit can be modeled as a resistor A resistor is a device which contains a defined amount of resistance and is used to control current in an electronic circuit

Resistors

Load Resistances I + V L - In an electronic circuit, current flows into the load resistor establishing a potential difference across it in the polarity shown

Energy Dissipated into a Load Resistor + - E-Field I e A B The energy dissipated into a load resistor is the energy delivered by the battery per unit time: