Ch Electricity II. Electric Current  Cell and Battery  Potential Difference  Current  Resistance  Ohm’s Law

A. Cell and Battery  Cell  a device that produces an electric current by converting chemical energy into electrical energy  A cell conducts a current  Battery  made up of many cells and also converts chemical energy into electrical energy

C. Current  Current  flow of electrons through a conductor  depends on # of electrons passing a point in a given time  measured in amperes (A)

D. Resistance  Resistance  opposition to the flow of electrons  electrical energy is converted to thermal energy & light  measured in ohms (  ) Copper - low resistance Tungsten - high resistance

D. Resistance  Resistance depends on…  the conductor good conductors have low resistance  wire thickness less resistance in thicker wires  wire length less resistance in shorter wires  temp - less resistance at low temps

E. Ohm’s Law  Ohm’s Law V = I × R V: potential difference (V) I: current (A) R: resistance (  ) Voltage increases when current increases. Voltage decreases when resistance increases.

E. Ohm’s Law  A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? GIVEN: R = 160  V = 120 V I = ? WORK : I = V ÷ R I = (120 V) ÷ (160  ) I = 0.75 A I V R