ELECTRIC CURRENT AND ELECTRIC ENERGY Chapter 17 Section 1 and 2

Electric Charge: Objects become positively charged when they lose electrons and negatively charged when they gain electrons; objects with like charges repel and objects with opposite charges attract Electricity: flow of electric charges

ELECTRIC CURRENT  Electric Current is expressed in units called amperes-often shortened to amps.  The symbol for ampere is A. The symbol for current is I

All matter is composed of positive and negative particles. The flow of charged particles is an electric current.

 When you flip a switch, an electric field is set up in a wire at the speed of light.  The electric field causes the free electrons in the wire to move. The energy of each electron is transferred instantly to the next electron.  The electric field is created so quickly that all electrons start moving through the wire at the same instant.

When you watch TV, use a computer, or even turn on a light, you depend on moving charges for the electrical energy that you need.

Higher Current = More Electric Charges Moving

ELECTRIC CURRENTS ARE LIKE ROLLER COASTERS. THEY FOLLOW A FIXED PATHWAY.

TWO TYPES OF CURRENT AC (Alternating Current)DC (Direct Current)  The charges continually shift directions. This shift in direction is caused by a reverse in polarity within the object that generated the current.  Example: The electric current in your home is AC  The charges always flow in the same direction.  Example: The electric current produced by batteries is DC AC/DC What is the Difference

VOLTAGE  Voltage-the potential difference between two points in a circuit; it is the “push” behind the electricity.  Voltage is expressed in volts (V). In equations, the symbol for voltage is the letter V.  Voltage is a measure of how much WORK is needed to move a charge between two points.  As long as there is voltage between two points on a wire, charges will flow in the wire

Voltage is what moves the current just like a hamster moving on a wheel will allow it to move. As long as the hamster keeps running, the wheel keeps moving.

RESISTANCE  Resistance is the opposition to the flow of electric charge  Resistance is expressed in ohms ( Ω, Greek letter Omega). In equations, the symbol for resistance is the letter R.  Resistance can be thought of as electrical friction. The higher the resistance of a material, the lower the current flow through the material.  If voltage doesn’t change, as resistance goes up, current goes down.

THINK ABOUT THIS… If you think of current as cars traveling on the road. The number of cars represent the amount of voltage. If there is not a road block, or resistance then the traffic, or current can move freely. If there is a road block, or resistance the current (cars) experiences difficulty in moving. The number of cars, or voltage, stays the same as resistance goes up and current decreases.

RESISTANCE VARIES An object’s resistance varies depending on its composition, thickness, length, and temperature. As resistance increases, current decreases.  Thicker-less resistance due to multiple path possibilities  Shorter-less resistance due to less distance to flow  Colder-less resistance due to material’s particles not moving around, so doesn’t bump into the moving charges

GENERATING ELECTRICAL ENERGY  Energy cannot be created or destroyed. It can only be transformed or changed into other kinds of energy.  Many things change different kinds of energy into electrical energy.  Generators convert mechanical energy to electrical.  Cells and batteries convert chemical or radiant energy into electrical energy.

TWO KINDS OF CELLS Wet Cells Dry Cells  Liquid electrolytes  A car battery is made of several wet cells that use sulfuric acid as an electrolyte  Solid or paste-like electrolyte  Batteries used in small radios and flashlights

THERMOCOUPLES ARE DEVICES THAT CONVERT THERMAL ENERGY INTO ELECTRICAL ENERGY. PHOTOCELLS ARE DEVICES THAT CONVERT LIGHT ENERGY INTO ELECTRICAL ENERGY.