Electricity & Magnetism

2. Electricity & Magnetism Day 5 February 19, 2014 Wednesday

3. Apple Battery Review • Zinc and Copper pushed in 1 cm • Zinc and copper react with the acid in the apple to produce an electrical current. Electrons carry a charge from the zinc nail (electron donor) through the wire and the meter to the copper wire (electron acceptor). The chemical energy in the acid is being converted into electrical energy. • Because the zinc nail has less electron affinity, it loses electrons and zinc nail is positively charged. • Because the copper has a greater electron affinity than the zinc nail, it gains electrons copper makes the copper wire negatively charged. • This creates imbalance in the charge between the two metals, causing the meter to go up as the electrons flow from the zinc to the copper.

4. #3 – copper wire 4 cm and zinc nail 1cm • What happened? • Did the meter move much? • When the zinc nail is pulled out the of the apple so that only a little remains in the apple, the current drops. This is because there is less zinc to react with the acid, consequently less zinc to give up electrons. (zinc-electron donor)

5. Which configuration showed the greatest change in the meter? • The more of the metal that was pushed in the apple, the more metal there was to react with the acid in the apple so more chemical energy was converted into electrical energy.

6. What happened when the copper wire and the zinc nail touched? • What happened to the meter? • No current • Why? • It appears that there is no current traveling from the zinc to copper. There are however electrons flowing from one to the other. Instead of flowing through the meter, the electrons are flowing straight from one metal to the other. Electrons always take the easiest path. • This is called a short circuit, because the electrons are taking the shortest path. • So when you hear that a circuit has been shorted… • A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path, often where essentially no (or a very low) electrical impedance is encountered • In electrical devices, unintentional short circuits are usually caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended.

7. Short Circuit • Short circuits are generally to be avoided, as they result in very high rates of electron flow, causing wires to heat up and battery power sources to deplete. If the power source is substantial enough, a short circuit may cause heat of explosive proportions to manifest, causing equipment damage and hazard to nearby personnel. This is what happens when a tree limb "shorts" across wires on a power line: the limb -- being composed of wet wood -- acts as a low-resistance path to electric current, resulting in heat and sparks.

8. The importance of fuses • What does it mean to “blow a fuse”? • What is a circuit breaker? • These are “tripped” or “blown” when a circuit is shorted. • When short circuits, happen, the large flow of current produces heat. Heat is dangerous for the components and also can cause fires to start. • A fuse stops the flow of electricity in the circuit. If you have a problem with something electrical in your car, check the fuse!

9. Circuit breaker • A circuit breaker is an automatically operated electricalswitch designed to protect an electrical circuit from damage caused by overload or short circuit • Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. • Fault detected – circuit breaker must open to interrupt circuit • some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts • http://www.youtube.com/watch?v • =8YJrhRo8UL0

10. The switches are called GFCIs: Ground Fault Circuit Interrupters. Confused? Me too. So I talked to John Drengenberg, the Consumer Safety Director for Underwriters Laboratories, the folks who for more than a century have been checking the safety of nearly everything in your house that could kill you. (In an average home, about 125 devices carry a “UL” seal of approval.) • How do GFCIs work? If you drop an appliance (like a hair dryer) into water (say, in a tub), things head south quickly. Electricity surges into the water and down the drain pipe like lightning seeking ground. If you’re in the tub, your heart can go into fatal fibrillation. (Drengenberg, whose job it is to think about such things, notes that human blood is a particularly fine electrical conductor.) As mentioned above, the flow of AC (alternating current) power is constantly being reversed. The clever GFCI checks that the flow of power out of a device matches the flow going in. If the power isn’t coming back, then it’s going somewhere else…bad—in which case the GFCI cuts off the power. so a GFCI trips when too much power flows through in relation to how much is returning,not because of a net increase in power flow.  • According to Drengenberg, GFCIs have been around for about twenty years now. In the U.S., they were first mandated in bathrooms. Now, in most municipalities, they’re obligatory in kitchens, garages, outdoor and swimming pool areas, and even basement outlets. (They’re mandated when you build new or extensively renovate.) • A GFCI is not like a circuit breaker, which is designed to prevent fire and which works so slowly that it would never activate in time to prevent an electric shock injury. A GFCI, in contrast, reacts in 20-25 milliseconds, well before your heart would have a chance to go bananas.

11. What happens if you replace a zinc nail with copper wire? • If you have both copper and copper… • There should be no current because copper cannot be both a donor and acceptor when used together. T • There is no donor to give up electrons. There is no acceptor to accept the electrons. • This is because they have equal electron affinities.

12. What is energy? • Energy: the ability to do work • What do you already know about energy? • Makes things move • Car is moved by burning gasoline • Sailboat is moved by wind energy • Baseball moved by the energy in a persons arm • Bullet moved by exploding gunpowder • What other things does energy help us do? • Makes things move • Makes heat • Makes light • Makes technology work (run electrical devices) • Makes things grow

13. How does increasing the depth of the metals affect amount of energy? • INCREASING THE DEPTH OF THE NAIL INCREASES THE CURRENT BECAUSE THERE IS MORE METAL TO REACT WITH THE ACID • Now, complete your explanations… • Turn to the front side where it says electrical current and insulators.

14. Bonding • We have learned about metals, nonmetals and semimetals. We have even bonded many of these. • Metal + Nonmetal = • Ionic Bonding • 2 Nonmetals = • Covalent Bonding • What happens when two metals come together? • Metallic Bonding

15. Metals form giant structures in which electrons in the outer shells (valence electrons) of the metal atoms are free to move. • The metallic bond is the force of attraction between these free electrons and metal ions. • Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points. • “Sea” of delocalized electrons

16. Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. • The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile.

17. Insulators and Conductors • What do you think the term conductor means when talking about electricity? • a conductor is an object or type of material which permits the flow of electric charges in one or more directions. For example, a wire is an electrical conductor that can carry electricity along its length. • What do you think an insulator is? • An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field

18. Turn in Taste the Power • Cross out the data table, there’s no time!

19. Light a bulb-inquiry • Materials • Light bulb • One wire • D Battery • Use the simple materials provided (and nothing else) to light the bulb • What caused the battery to light? • Moving Electrons!!!