“Charge it today!”

Charges were first discovered in ancient Greece when cloth was rubbed on amber and the amber attracted bits of straw to it. It was Ben Franklin that named the charges as “positive” and “negative.” Charges come from an inbalance between the number of protons and the number of electrons. Like charges repel and unlike charges attract each other. Charges

Static electricity is the collection of electrical charges on the surface of an object. When two objects are rubbed together, electrons may transfer from one object to another. Electrons are gained or lost from a material depending on the other material it contacts. The “electrostatic series” lists these in order. Static Electricity

Electrostatic Induction The charged rod repels like charges further into the paper and attracts opposite charges towards itself.

Grounding Benjamen Franklin invented the lightning rod. A metal plate is placed in the ground and connected to a metal wire that connects to a pointed metal conductor above the roofline.  Electrons in the ground flow up the lightning rod toward the positive charges in the cloud and neutralize the charge in the cloud.

Grounding, cont. Earth is so large that it is able to store excess of either type of charge safely. Houses have their electrical outlets “grounded”.

Electrical field  It’s the area around the electric charge that is able to exert a force on other electric charges.  It depends on the distance between the charges and the size of the charges.

Current electricity is flowing electrical charge through a conductor. Current Electricity

Lightbulbs

Circuit is an unbroken path through which electrons can flow.

Electrical Circuits…  Simple circuits will be made of a source of energy (such as a dry cell) and conductor (such as a wire). A resistor may be added to this, such as a bell, light, buzzer, etc. Switches may be added to open (stop the flow of electrons) and close the circuit (allow the flow of electrons.)

Diagramming a circuit… bulb motor

Which materials allow electrons to flow and which don’t? ConductorsInsulators Conductors allow electrons to flow freely. Name some: Insulators don’t allow electrons to flow freely, they “resist” the flow of electrons. Name some:

Potential difference  Charges will tend to move from one place if there is a “potential difference”, in other words, if there is a difference in the amount of charge between two objects.  Think of it like two water tanks connected with a valve. One has more water. The pressure from the higher side, where they are connected, will cause water to flow to the lower side when the valve is opened.

When the valve opens… Pressure to the right side of the valve will make the water flow from the right to the left until they “even” out – the same happens with a current due to the potential difference. (It creates what is called the “electromotive force.”)

is measured in amperes (“amps”). Amperes measure the amount of current. It’s how much charge passes by per unit of time. Think of it as “how much water is flowing through a pipe.” It is symbolized by “I”. An amp is 6.3 billion billion electrons per second!! Electrons in your house’s wires don’t move fast – only the current does because the electrons are so tightly packed in the metal wire. (It may take 3 hours for an electron to move 1 meter!!) Current…

Charge travels quickly, though electrons travel slowly (they keep colliding with one another and other things!) Picture a pipe full of water, if you turn the faucet on, water will immediately come out the other end. This is why a light goes on as soon as you throw the switch.

Current, cont.  Electrons flow from the negative terminal of a dry cell through and back to the positive pole. BUT…  The current is said to follow the motion of the positive charges, which is in the OPPOSITE direction. We can thank Ben Franklin for this who knew nothing of electrons and just decided to DEFINE current flow according to the flow of the “positive” charges.  So, current is said to flow from the positive terminal of a dry cell, through the circuit, and back to the negative terminal.

Voltage  Volts are the units that measure the potential difference, in other words, the force with which the electrons are moving through the conductor. It measures the size of the “push” of the electrons through the circuit.  Volts are symbolized as “V”.

Think water tank, again… Here is a way to think about voltage. If you raise that bucket of water up the water will run out with more force through a hose to a lower bucket due to its higher potential energy.

Dry cells or other electrical sources provide the voltage or potential difference. The greater the voltage the greater the potential difference or push of the current through the wire. Putting dry cells together, end-to-end, creates a greater voltage. Voltage, cont.

Resistance  Just like a pipe will resist the flow of water, a conducting wire offers resistance to current flow.  The unit used to measure resistance is the ohm.  Heat can build up in the conductor if it has a higher resistance (remember how some energy always gets changed to thermal energy?!). Copper has a very low resistance.

Resistance depends on…  Resistance of a wire depends on what it’s made of. And just like a water pushing through a pipe, the narrower and longer the wire the greater the resistance. Which of these would have the greatest resistance?

Why are long extension cords thick instead of thin? Shorter ones can be thin. Why is it dangerous to string extension cords together?

Ohm’s Law  G. S. Ohm found that there was a relationship among the current strength (amps, I), the potential difference (volts, V), and resistance (R) to the flow of the current on the wire.  I = V/R This is called Ohm’s Law. In other words, the current (amps) is equal to the force of the current (volt) divided by the resistance.

Kinds of Circuits Series circuits have all the resistors in a row on the wire connecting them to the electrical source. As the current passes through each resistor, some of the current is lost as heat in the resistor, reducing the number of amps that reach the next resistor.

Kinds of circuits, cont. Parallel circuits are designed with each resistor having its own path for the current. The amperage and voltage remains constant for each path.

Electrical power  The rate at which an electrical device, such as a hair dryer, uses electrical current to change it to another form of energy (such as thermal, radiant, or mechanical) is called power.  It is related to the number of electrons flowing (current) and the force (voltage) with which the charge is flowing.  Power is measured in “watts”.  P (watts) = I (amps) X V (voltage)

Check. Do you know these terms?  charge  static electricity  electromagnetic induction  grounding  electric field  circuit  conductor  insulator  Resistor  dry cell  potential difference  closed circuit  open circuit  current  amperes  voltage  resistance  series circuit  parallel circuit  Ohm’s Law  watt