Static Electricity the net accumulation of electric charges on an object Electric Field force exerted by an e - on anything that has an electric charge opposite charges attract like charges repel
Static Discharge the movement of electrons to relieve a separation in charge
Conductor material that allows electrons to move through it easily e - are loosely held ex: metals like copper and silver
Insulator material that doesn t allow electrons to move through it easily e - are tightly held ex: plastic, wood, rubber, glass
Electroscope instrument that detects the presence of electrical charges leaves separate when they gain either a + or - charge
The flow of charges (usually electrons) through a wire or conductor. Measured in amperes (A or amps)
ALWAYS flows from High to Low voltage A voltage difference is the push that causes charges to move. Measured in volts (V)
For charges to flow (to have current or voltage) a wire must always be connected in a closed path
A - battery B - switch C - light bulb D - resistor
Dry Cell Battery Produces a voltage difference between its zinc container and its carbon suspension rod Causes current to flow between them
Wet Cell Battery Contains two connected plates made of different metals (usually lead) in a connected solution (usually sulfuric acid) Car, truck and tractor batteries
Wall Socket Has a voltage difference across the two holes of an outlet. Generators at power plants provide the voltage difference
The tendency for a material to oppose the flow of electrons Changes electrical energy into thermal energy and light All materials have some electrical resistance Copper - low resistance Tungsten - high resistance
Measured in Ohms (Ω) Resistance increases with Increased length Decreased diameter Increased heat Think of a garden hose
Current = Voltage / Resistance
A lightbulb with a resistance of 160 is plugged into a 120-V outlet. What is the current flowing through the bulb? GIVEN: R = 160 V = 120 V I =? V WORK: I = V R I = (120 V) (160 ) I = 0.75 A I R
What property of electric current causes light bulbs to give light?
Resistance. As electrons flow through the filament, the filament resists their flow and changes electrical energy into thermal energy and light.
Rely on generators to produce a voltage difference across the outlet causing charge to move when the circuit is complete
Current only has one path (or loop) to follow Example: Some holiday lights
current is the same throughout circuit lights are equal brightness each device receives a fraction of the total voltage get dimmer as lights are added If any part of the circuit is broken, the current stops flowing
Current only has two or more paths (or branches) to follow Example: Electric system in a house
current travels in multiple paths one break doesn t stop flow current varies in different branches takes path of least resistance bigger light would be dimmer each device receives the total voltage no change when lights are added
Use parallel circuits in a logical network Each branch receives the standard voltage from the electric company too many devices can cause wires to overheat
Enters your home at the circuit breaker/fuse box Branches out to all your outlets Like your Heart and blood vessels
Guards against overheating electric wires Contains a small piece of metal that melts if current becomes too high.
Guards against overheating electric wires Contains a small piece of metal that bends when it gets hot
Can be converted to Mechanical energy Thermal energy Light energy
The rate at which electrical energy is converted from one form to another Measured in Watts (W) Power = Current x Voltage Difference P (W) = I (A) x V (V)
P: power (W) P = I V I: current (A) V: potential difference (V)
A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use? GIVEN: I = 0.01 A V = 9 V P =? P WORK: P = I V P = (0.01 A) (9 V) P = 0.09 W I V
Unit of electrical energy is the Kilowatt-Hour Equals 1000 Watts of power used for 1 hour Energy = Power x Time E (kwh) = P (kw) x t (h)
E = P t E: energy (kwh) P: power (kw) t: time (h)
A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kwh) is used in one day? GIVEN: P = 700 W = 0.7 kw t = 10 h E =? E WORK: E = P t E = (0.7 kw) (10 h) E = 7 kwh P t
Does your home have a fuse box or circuit breaker? Why is it there? How does it work?
It is there to make sure the electrical wires in our home do not get too hot and start fires. If the wired get too hot, they melt the piece of metal in the fuse or bend the piece of metal in the circuit. This opens the circuit and stops the flow of current. If we have a fuse box, we have to replace the melted fuse with a new one. If we have a circuit breaker, we only need to unplug some appliances and flip a switch.