Cells have positive and negative electrodes. Electrons build up on the negative electrode. Current is the amount of e- moving – coulomb Current is measured in Amperes. Voltage is the difference between the potential energy of electrons at two point in a circuit.

5.5 Volt battery 0 Volts 5.5 Volts + electrode - electrode electrolyte paste 5.5 Volts

Circuits can either be opened or closed by a switch. e- ● + - ● + - e- Open circuit (off) Closed circuit (on)

Resistors, loads and Ohm’s Law

Electrons lose energy as they move through things. Resistor: electrical device in a circuit that takes potential energy from electrons – resistance. Electrical symbol – R Unit is the ohm (Ω) The loss of potential energy over a resistor is called the “voltage drop” Schematic Symbol

Resistors are sometimes used to reduce the energy of a circuit for safety reasons. Any resistor that takes the energy and converts for use – load. Mechanical Energy Thermal Energy

e- + - e- Load a resistor that converts energy. Resistor lowers energy ● + - Load a resistor that converts energy. e- Resistor lowers energy removed as heat

Ohm’s Law - The voltage in a wire is equal to current multiplied by resistance.

A bulb that has 2. 4 A flowing through it, has a resistance of 16 Ω A bulb that has 2.4 A flowing through it, has a resistance of 16 Ω. Calculate the voltage drop across the load – energy lost by the electrons to light up the bulb. e- ● + - V = I · R 38.4 V = (2.4 A) · (16 Ω) = 38.4 V e-

A 9 V battery is hooked up to a metal wire to make a circuit A 9 V battery is hooked up to a metal wire to make a circuit. If the metal wire has a resistance of 6.5 Ω, calculate the current in the wire. e- V R I = ● + - 9 V 6.5 Ω = e- = 1.38 A

V I R Voltage – Energy lost by the electrons through the circuit. Current – Number of electrons moving through the circuit. Resistance – the ability of a load or resistor to take energy. I R V