Coulomb's Law: F= k (q1q2) / d^2
There are two types of polarization: Friction and induction
-friction --> Friction is the resistance of motion when one object rubs against another. Anytime two objects rub against each other, they cause friction. Friction works against the motion and acts in the opposite direction
-induction -->
How does a balloon stick to a wall after rubbing it against your hair?
- when you put a balloon to your hair, the balloon takes away the hairs electrons and causes the hair to be positive and the balloon to be negative. when you pull the balloon away, the opposite charges attract, causing the balloon and the hair to stick together. Because the wall is neutral and the balloon is negative, the wall polarizes causing a greater force. Coulomb's Law says that charges that attract cause a greater force and charges that repel cause a lower force. The net force on the balloon is attractive so the balloon sticks to the wall.
Electric Fields
- A positive charged particle finds itself in an electric field. It moves to the left and increases velocity. Is the electric field caused by a positive or negative charge? Explain. It could be both or a mixture because the positive charge could be moving away from the positive charge or towards the negative charge.
- Something is safe inside an electric case because the metal case creates an electric field that protects anything inside of it causing it to have a 0 net force on objects in the box
- a region around a charged particle or object within which a force would be exerted on other charged particles or objects.
EP/EPD and capacitors
- Electric potential --> total PE/q --> J/c or V
- Electric potential difference --> Change PE / q --> V
- Why can something with high voltage be less dangerous than something with low voltage?
--- Something that has a high voltage can have fewer charges but something with low voltage can have more charges. Total Energy is what is dangerous.
- If a bird were to fly through the wires and touch both wires with its wings, the bird would be completing the circuit. when both wings complete the circuit there is a large potential difference so the voltage is higher and the bird gets electrocuted.
- Voltage --> energy given to each coulomb of charge measured across 2 points
Resistance --> resists the flow of charge --> ohms
Ohm's Law --> V=IR
Power--> P=VI
More resistance --> Longer, thinner, hotter
Less resistance --> Shorter, thicker, colder
2d = 1/4F
1/2d = 4F
Charged --> imbalance of protons and electrons. In order to charge an object we have to transfer charges
Polarization --> A balance of charges within an object. Net charge = 0
Direct current --> Continuous electric current that flows in one direction only.
Alternating current --> flow of electric charge that periodically reverses directions
Parallel circuit--> 1/R total = 1/R + 1/R ... continues to stay on if one light goes out. Voltage is fixed. Resistance is cut in half. Current is added.
Series circuit --> R total = R1 + R2 +R3 .... If one light goes out, they all do. Resistance adds. voltage adds. Current stays the same
Why do bulbs burn when they first turn on? The bulb is cold and the filament is cold therefore resistance decreases which means current is high which means the filament will rapidly heat up and expand.
Total resistance when more appliances added for series --> Goes up parallel --> goes down
Current as more appliances are added --> Series goes down parallel goes up
Brightness as more appliances are added --> Series goes down parallel stays the same
What happens to the circuit when a light goes out --> Series all go out parallel not affected
How does a fuse/circuit breaker protect your house? Why is a fuse needed? How is a fuse wired and how does it work?
- Homes are wired in parallel so each device gets its own branch. This means each device gets the full voltage of the circuit (120V). it also means that the current of each device is added to the total, so as more devices are turned on, more and more current is drawn. if the current gets too high, it can over heat the wiring and cause a fire. this is what fuses protect from happening. At a certain current level, they will shut off all power from the circuit. To do this they must be wired in series with the rest of the circuit. A fuse blows by melting the wire inside.
Calculate how much it will cost to run a 60 watt light bulb connected to a 120 V source for 1 month if it costs .10 cents per Kwh
60 watts = .06 kw
1 month (30/ month)(24/day) = 720 hours
Energy = power(time)
= .06 kw (720 hours)
= 43.2 kwh
cost = .10/kwh (43.2 kwh)
= 4.32 dollars
Electrons originate from the body
Energy/Electric field moves at the speed of light
Current is a flow of charge. measured in Amps = coulombs/second
R increases I decreases
Current carrying wire is usually neutral
measure current --> R= V/I
Current decreases and filament increases because when filament increases, resistance increases
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