 Cells have positive and negative electrodes.

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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

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