Presentation on theme: "Cells have positive and negative electrodes. Electrons build up on the negative electrode. Current is the amount of e - moving – coulomb Current is measured."— Presentation transcript:
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.
●● + - ●● + - e-e- e-e- Closed circuit (on) Open circuit (off) Circuits can either be opened or closed by a switch.
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 EnergyThermal Energy
●● + - e-e- e-e- Load a resistor that converts energy. Resistor lowers energy removed as heat
Ohm’s Law - The voltage in a wire is equal to current multiplied by resistance. I R V V = I · R I = V R R = V I
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-e- e-e- V = I · R = (2.4 A) · (16 Ω) = 38.4 V 38.4 V
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-e- e-e- I = V R 9 V 6.5 Ω = = 1.38 A
I R V 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.