Electricity

3 Methods for Charging Objects: Friction, Conduction, and Induction Human Hands (if very dry) Leather 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 (scotch tape) Polypropylene Vinyl (PVC) Silicon Teflon MORE negative MORE positive FRICTION Objects, when rubbed, can pick up net + or - charges _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Note: Fur is often used to give electrons, silk to remove electrons!

CONDUCTION Charge is transferred by objects contacting one another _ _ _ _ ______ _ _ _ _ _ _ _ _ _ _ _ _ _

INDUCTION One object induces a charge on another by rearranging charges on another when nearby (“induced dipoles”)

Simple Electric Circuit V = Potential Difference = Voltage Difference(voltage) in volts (V) I = Current in amperes (A) R = Resistance in ohms (Ω) I = V/R (OHM’s LAW)

Series Circuit What happens to the voltage and current if the number of bulbs increases? The number of batteries?

Series Circuit 2 I = V/R V = IR [ORIGINAL (1 battery, 1 bulb)] Voltage = V Resistance = R Current = I [ADD 1BULB (1battery, 2 bulbs)] Voltage = V Resistance = 2R Current = ½ I [ADD 2BULBS (1 battery, 3 bulbs)] Voltage = V Resistance = 3R Current = 1/3 I As bulb number increases, bulbs are individually dimmer!

Series Circuit 3 I = V/R V = IR [ORIGINAL (1 battery, 1 bulb)] Voltage = V Resistance = R Current = I [ADD 1 BATTERY (2 batteries, 1 bulb)] Voltage = 2V Resistance = R Current = 2 I [ADD 1 BATTERY (3 batteries, 1 bulb)] Voltage = 3V Resistance = R Current = 3 I As battery number increases, bulbs are individually brighter!

Parallel Circuit What happens to the voltage and current if the number of bulbs increases? The number of batteries?

Parallel Circuit 2 I = V/R V = IR [ORIGINAL (1 battery, 1 bulb)] Voltage = V Resistance = R Current = I [Add 1 bulb (1 battery, 2 bulbs)] Voltage = V Resistance = ½ R Current = 2 R [Add 2 bulbs (1 battery, 3 bulbs)] Voltage = V Resistance = 1/3 R Current = 3 R As bulb number increases, individual bulb brightness stays constant, but current level increases, and power source is drained more rapidly!

Parallel Circuit 3 I = V/R V = IR [ORIGINAL (1 battery, 2 bulbs)] Voltage = V Resistance = R Current = I [ADD 1 BATTERY (2 batteries, 2 bulbs)] Voltage = 2 V Resistance = R Current 2 I As the number of batteries is increased, bulbs are individually brighter (all having the same brightness), and current level increases!

Can You Identify each of these Circuit Types?

Component Connections Ammeter – connected in SERIES with power source Voltmeter – connected in PARALLEL in circuit Note OPEN vs CLOSED CIRCUIT

Electrostatic charge Configurations Equipotential lines are blue Electric Field Lines are red

Temporary Magnets Strength Variables 1)Material Used Fe › Al, Pb, Cu, etc. 2)#strokes (in the same direction!) by one pole of a permanent magnet #strokes … strength Note: naturally magnetic elements are iron(Fe), nickel(Ni), cobalt(Co), neodymium(Nd), and gadolinium(Gd)

The “Rules” of Electrical/Magnetic Field Lines Unmagnetized Material Magnetized Material 1)Field lines form complete loops. 2)Field lines come out of the N pole, go into the S pole. 3)The closer the lines, the stronger the field. 4)Field lines do not cross one another

Note: field lines point away from N, toward S Repulsion Attraction

Earth’s Magnetic Field

Electromagnet Variables: 1) Coil number Cn# …strength 2) Current (I) I …strength 3) Core material Fe › Al, Pb, etc. Notes: A solenoid is a single wire wrapped into a coil form; an electromagnet is a solenoid-wrapped iron core An electromagnet’s properties can be changed by controlling it electrical current!

Motor Changes electrical energy to mechanical energy 1.Brushes touch commutator…current flow…coil is attracted to permanent magnet, rotates… 2.Brushes lose contact w/commutator…no current…inertia keeps coil rotating… 3.Brushes contact opposite side of commutator…current reverses… magnetic field reverses, flipping coil… 4.Brushes lose contact with commutator…etc…coil keeps rotating! Motor Components Wire coil Permanent magnet Power source

Generator Changes mechanical energy to electrical energy Generator Components Wire coil Permanent magnet Outside energy source 1.Outside source causes coil to rotate through magnetic field…current flow… 2.After first ½ turn, ends of coil wire move past the opposite poles of permanent magnet…current changes direction…that’s why the current produced is called alternating current (AC)! OR 1.Fix the coil, and rotate the permanent magnet around it…etc (Rotating magnets can be attached to a large wheel (turbine) that rotates when pushed by water, wind, or steam)