Section 1 – What is Electricity? Chapter 16:Electricity Section 1 – What is Electricity?

Definition: electricity – energy transferred as protons or electrons flow. Electricity is caused by unbalanced electric charge. e- e- e- e- e- e- e- e- e- e- e- e-

Definition: electric charge - a property of matter based on the number of electrons on an object. Objects can gain or lose electrons to change their charge. Benjamin Franklin identified the property of electric charge and gave it the positive/negative name!

- + + + + - + - + + - - - + - + + + - - - Electric charge can be positive, negative, or neutral. Positive: more + than – Negative: more – than + Neutral: Same number of + and – - + + + + - + - + + - - - + - + + + - - -

Some materials allow charges to flow, while other objects stop the flow of electrical charges. Definition: electrical conductor – a material that allows charges to move freely. Definition – electrical insulator – a material that does not transfer charges easily.  CONDUCTOR NSULATOR 

Insulators / Conductors Some conductors: All Metals Salt Solutions (electrolytes) Silver is the best metal conductor! Some Insulators: Wood / Cloth Glass ; Plastic; Rubber; Air

Electric force is a property that is responsible for most of the common forces that we experience, like friction. Definition: electric force – the attractive or repulsive force between objects due to their charge.

Electric force exists as an invisible field around charged objects. It causes: Opposite charges attract. Like Charges repel. + A positive electric field pushes outward. - A negative electric field pulls inward.

+ + - + - -    That explains why opposites attract! The arrows are pointing in the same direction… - +  - - 

Definition: static electricity – a build up non-moving electric charges on an object. Static electricity is often produced by friction! Friction causes electrons to stick to some materials… As more and more electrons build up, the static charge increases.

Static Electricity Static discharge occurs when the static electricity flows away from its source.

Definition: electric induction – the process by which a charged object causes another object to become charged. Example: combing your hair causes static charge to form on the comb. The comb can then be used to charge pieces of paper.

Section 2 – Electric Current Chapter 16: Electricity Section 2 – Electric Current

MORE ELECTRONS = MORE CURRENT When electrons begin moving, they form a stream of electricity, called a current. Definition: electrical current – a measure of the # of electrons moving through a conductor. MORE ELECTRONS = MORE CURRENT Current is measured in amps (A).

Electricity is often discussed in terms of voltage. Do you have any idea what voltage is? Definition: voltage – the push that causes electric current to flow.

Yes, work has to be done to move electrons! Voltage measures the amount of work that must be done to move a charge. Voltage has units of volts, V. Yes, work has to be done to move electrons! The voltage on a battery, for instance, tells how much work that battery can do.

Electric Current Do you think a 1.5 volt battery can power a car? Of course not!! The car needs a 12 volt battery. The 1.5 v battery doesn’t produce enough force to move all of the electrons needed to run the electronics.

Speaking of batteries… Definition: battery – a device able to convert chemical energy into electrical energy. Batteries DO NOT store electricity! So, how do batteries work? Each battery contains an electrolyte (an acid), a cathode, and an anode. Definition: cathode – the + end of a battery. Definition: anode – the - end of a battery.

A neg. charge collects on the anode. The charge flows to the cathode when connected by a wire.

Each of the batteries below have the SAME voltage, but are used in different electronics. What is different about them? THEY PUSH DIFFERENT AMOUNTS OF ELECTRONS…WITH THE SAME AMOUNT OF FORCE.

Its kinda like… The water is moving at the same speed, but different amounts of water are being moved! The amount of water represents current (amps)…in case you didn’t figure that out yet. Moving a small amt. of water at 10 mph. Moving lots of water at at 10 mph. Think AAA battery… Think D-Cell battery…

Definition: resistance – opposition to the flow of electric current. When a current cannot flow through a material easily, it is encountering resistance. Definition: resistance – opposition to the flow of electric current. In other words, resistance slows down or stops the flow of electrons. Electric insulators cause almost 100% resistance. Enough resistance to stop the flow of electricity.

Electric Current Resistance is a form of friction. Resistance can cause some electric energy to be converted into thermal energy… Electric stoves work by using that fact! Electricity flows through The coil, which causes resistance.

Why is knowing resistance important? Resistance is how incandescent light bulbs work. Electricity travels through the wire coil and encounters resistance. The coil becomes hot from the resistance, and begins to glow. Inside the bulb, argon gas keeps the filament from catching on fire. Most filaments are made from the element Tungsten.

LED bulbs and fluorescent bulbs do not require as much electric current as incan. bulbs. So…LEDs and Fluorescent bulbs are very “energy efficient”!

Chapter 16:Electricity Section 3 – Circuits

What is a circuit? When you flip the light switch, the light comes on…obviously. What does the switch have to do with it?? The switch on the wall is part of a circuit. When it is switched to the ON position, it allows electric current to flow into the light bulb.

Whenever current flows, it encounters resistance. We can measure this resistance with: The Resistance Equation (Ohm’s Law): Resistance = Voltage/Current R = V/I Resistance is measured in Ohms (Ω).

Circuits Definition: circuit – a set of components that allow one or more complete paths for electric current to flow. Any time electricity is flowing, a circuit is present.

Circuits When electricity is able to flow freely through a circuit, that circuit “closed”. Incomplete circuits will not allow electricity to flow freely. They are called “open” circuits.

Types of Circuits Definition: series circuit – a circuit that forms a single pathway. Electricity can only flow one way in a series circuit.

Types of Circuits Definition: parallel circuit – a circuit that forms multiple pathways for electricity. Parallel circuits can have a piece removed from them and still allow electricity to flow in another part of the circuit.

Resistance in Circuits It is useful to know the resistance of objects in circuits. There are two rules used to calculate it: Series circuits have a total resistance of: RT = R1 + R2 +R3….. In other words, you add up the value of all the resistors. Parallel circuits have a total resistance of RT = 1/(R1 + R2 + R3…..) That’s all there is to it.

Circuit Components Circuits consist of many different things. The most common components of a circuit are: Power Supplies Wires Resistors Bulbs Switches Definition: resistor – a device that blocks SOME (not all) electric current in a circuit. Appliances like TV’s, lights, computers…these are all resistors.

Electric Current in wires…. Electric resistance explains why electronics get hot as they run. Even conductors cause some resistance. As a wire gets thicker, there is less resistance. Lots of Resistance Some Resistance Little resistance

Electric Current in wires…. As a wire gets shorter, there is less resistance. Lots of Resistance Some Resistance Little resistance

Electric Current in wires…. As a wire gets thicker it can carry more electric current.

Basic Circuit Symbols (copy these to notes!) Resistor Wire Battery or Power Source Bulb Open Switch Closed Switch