ELECTRIC CHARGES CURRENT By Mr Frank Todd Notes

ELECTRIC CHARGES & CURRENT By Mr. Frank Todd Notes provided by Mr. Joe Martonik

A. Electric Charges & Static Electricity • • • 1. Types of Electric Charge & Interaction Protons= + charge Electrons= - charge Like charges repel (+ +, - -) Unlike charges attract ( + - )

• 2. Electric Fields • The area around electric charges that has the force of the charge exerted on it. • When a charge is placed in an electric field, it is pulled or pushed. • The field is the strongest near the charged particle.

• 3. Static Charge: Results from a build up or redistribution of charge on an object. • Charged Objects: – Some materials hold their electrons well (insulators). Some do not and the electrons move freely from atom to atom (conductors). – A neutral object can become charged by gaining or losing electrons. – A build up of charges is called static electricity. – (The charges build up but do NOT FLOW)

Give up electrons easily Triboelelectric series Gain electrons easily • Human hands (usually too moist, though) Very positive • Rabbit Fur • Glass • Human hair • Nylon • Wool • Fur • Lead • Silk • Aluminum • Paper • Cotton • Steel Neutral • Wood • Amber • Hard rubber • Nickel, Copper • Brass, Silver • Gold, Platinum • Polyester • Styrene (Styrofoam) • Saran Wrap • Polyurethane • Polyethylene (like Scotch Tape) • Polypropylene • Vinyl (PVC) • Silicon • Teflon Very negative

• Transferring Charge: Charges can be transferred by the following ways. – Friction—by rubbing materials against one another

• Transferring Charge: Charges can be transferred by the following ways. – Conduction—by direct contact between two objects

• Transferring Charge: Charges can be transferred by the following ways. – Induction—movement of electrons to one side of an object. (Caused by an electric field of another object)

• Static Cling: Clothes stick together because each piece of clothing contains opposite charges. What caused the clothes to be charged? • Rubbing between clothes as they tumble about in the dryer.

• 4. Static Discharge: – When there is a loss of static electricity as electric charges move off an object, it is called static discharge. – Humidity: Water molecules in the air can pick up electrons which may be in the process of being transferred. Charge then cannot build up on an object.

• 4. Static Discharge: – Sparks & Lightning: – A spark results when electrons jump from one object to another. – Lightning is a giant spark created when water droplets become charged by swirling wind during a storm. Electrons collect in the lower part of the clouds. To restore a neutral condition, electrons jump from the clouds to the ground.

• 5. Detecting Charge: – An electroscope is a device used to detect electric charge. – The device cannot tell if it is storing + or – charges. – Can only detect the presence of a charge.

B. Circuit Measurements • 1. Electrical Potential: • It is the potential energy per unit of electric charge. • Electrons flow from places of higher potential to places of lower potential. – This called Potential Difference.

• 2. Voltage & Sources: • Voltage is measured by a voltmeter. • Potential difference provides the force that pushes charge through a circuit. • This force is called the Volt. • Electrons will flow in a circuit as long as there is a potential difference or voltage between 2 parts of a circuit. • As voltage increases the flow of electrons increases. • Batteries and Generators serve as voltage sources.

• 3. Resistance: The opposition to flow of electric charges in a circuit. • The greater the resistance in a circuit, the less current or flow of electrons for a given voltage. • Influences on Resistance: – A wires length and thickness – Thick + Short wires = low resistance – Temperature—Low temperature= lower resistance • Ohms= unit for measuring Resistance

• 4. Current: Is the number of electrons passing a point in a given amount of time. • Current always flows through a path of least resistance. • Current will increase/decrease based on the battery construction or source of electrons. • Amps=unit of measuring current • Measured by an Ammeter.

Common tools and their Amperage bug killer 1 -2 fan = 1 -3 hedge trimmer 23 weed trimmer 2 -4 electric drill 3 -6 saber saw 4 -8 sander 4 -8 band saw 5 -12 lawn mower 6 -12 grinder 7 -10 chain saw 7 -12 drill press 7 -14 belt sander 7 -15 shop vac 8 -14 lawn edger 9 -10 air compressor 9 table saw 12 -15 snow blower 1215 circular saw 1215 1/4 HP motor = 6 1/2 HP motor = amps 10 amps 3/4 HP motor = 14 amps 1 HP motor = 16 amps router 8 -13

• • • 5. Ohm’s Law Resistance = Voltage/Current Ohms = Volts/Amps R= V/I V= Rx. I I = V/R V : : R x I

• Sample Problem: • A 0. 40 amp current is produced when a 12 Volt battery is connected to a headlight. How much resistance is produced by the headlight? • R=V/I • R= 12 V/0. 40 Amps • R= 30 Ohms

C. Series and Parallel Circuits • 1. Series Circuits • A circuit where all the parts are connected “one after the other” creating only one path for the flow of electrons. • If one bulb in a series circuit burns out or is removed the circuit is broken and all the bulbs go out. • As more bulbs are added, they get dimmer b/c the resistance increases. • Ammeters should be wired in series.

C. Series and Parallel Circuits • 2. Parallel Circuits • Different parts of the circuit are on different branches. This type of circuit provides different paths for the electric current. (Each bulb has it’s own path. ) • If one bulb is removed or burns out there are other paths for the current to take so the other bulbs stay lit. • Parallel circuits glow brighter because more current flows to the bulbs. • As more branches are added to a parallel circuit the resistance decreases. • Voltmeters should be wired in parallel.

Label each type of circuit below. Bulb Series Parallel

• 3. Household Circuits: • Must be wired in Parallel • Electricity is fed into a home by Thick and Heavy wires called lines. These have low resistance. • Parallel branches extend from the lines to the wall sockets and Appliances. • Switches are placed to control branches of circuits one at a time. • Voltage in house circuits is 120 Volts.

D. Electrical Safety • 1. Becoming Part of a Circuit • Short Circuit—A connection that allows a current to take an unintended path. • If you touch an exposed wire in the house, 120 Volts of current will pass into your body. This is called a SHOCK.

• 2. Grounding: • Additional wire in circuit to protect a person from shock. • Plugs have a 3 rd prong. This connects the metal shell of the appliance to the ground wire of the building. • Lightning rod-metal rod mounted to the roof of a building. If lightning strikes the rod the energy flows down the rod to a ground wire and then into the Earth.

• 3. Fuses and Circuit Breakers: • When a wire carries more current than it is designed to carry it will get HOT. The insulation will then burn. • Fuse-A device with a thin strip of wire (metal) that will melt if too much current flows. This is part of the circuit. (When the fuse melts or “blows” the circuit is broken. ) • Circuit Breaker- device which uses an electromagnet to turn off a circuit when it is overloaded.

• 4. Electric Shocks: • The human body depends on tiny electrical pulses to control many processes (ex. Heart beat) An electrical shock may disrupt these processes. • The severity of the shock depends on the current. A current of 0. 2 amps will burn and travel across the body and could stop the heart. • Current of an electric shock is related to voltage and resistance. • Your body has a low resistance (ions in fluids) • When wet your bodies resistance is hundreds of times lower.