A. Charges and Polarization including Coulomb's law
- Types of charges
- Positive
- Negative
- Opposite charges attract
- Positive charges will be drawn to negative charges and will be repelled by positive charges and vice versa
- An object can be
- Positively/Negatively Charged
- This mean the electrons or protons outnumbers the other causing the object to be overall charged
- Neutral
- Polar
- All protons go to one side and electrons go to the other giving it charged sides but remaining with an overall neutral charge
- Non-Polar
- Protons and electrons are evenly distributed
- Three ways an object can become charged
- Induction
- Lightning
- Contact
- Static Electricity
- Contact
- Balloon on Wall
- Coulomb's Law is used to measure the attraction between two charges
- In this formula distance has the biggest impact because it is squared
B. Electric Fields
- An electric field is the area around a charge that can influence another charge
- How close two things must be to attract or repel one another
- Arrows
- An arrow of an electric field shows the direction in which a PROTON would go in that electric field
- In the picture above, the proton would be repelled from the proton and attracted to the electron
- Electric Shielding
- A force within a sphere that will feel no force
- Metal keeps electricity
- Examples
- Seran Wrap on a Bowl
- Electronics encased in metal
C. Electric Potential/Electric Potential difference, Capacitors
- Electric Potential measure how much power something can put out
- Only matters if there is a difference in electric potential
- Birds on the electric lines
- The lines are far enough apart so that the birds never touch another wire and get shocked
- This is because the lines have difference electric potential and the bird would complete a circuit between the two
- A difference in electric potential is voltage
- Capacitors
- Two sides
- Positive
- Negative
- The sides are attracted
- They are briefly connected and emit energy
- Example
- Flash on a camera
- When they are connected light is emitted and the flash then goes off and shines a light
- D. Ohm’s law and electric potential difference
- I= Current
- Amps
- V= Voltage
- Volts
- R= Resistance
- Ohms
- Current is directly proportional to voltage applied to a device
- Current and resistance are inversely proportional\
- Resistance
- To increase resistance, increase thickness of the wire
- To increase resistance decrease temperature
- Example questions:
- A circuit has a current of 40 amps and a voltage of 20. What is the Resistance?
- 2 ohms
- A circuit has a 120V and 60 ohms of resistance. What is the current?
- 2 amps
- The only reason why a circuit has voltage is because there is a diffence in two volts. Each side has a different amount of
E. Types of Current, source of electrons, Power
- Types of Current
- Alternating
- The electrons within this circuit move back and forth
- Start by going forward then reverse directions
- Direct
- The electrons within this circuit move in the same direction at all times and go around the circuit
- Where do electrons come from?
- When we get power from the power company, a common misconception is the idea that we pay for the electrons. This is not true. We pay for current which causes the electrons to move. The electrons are already in the wires and running through our homes, but we must have current for them to move.
- Power= Current*Voltage
- Measured in watts
- Also defined as work over time
- Rate at which work is done over a certain amount of time
- J/s
F. Parallel and Series Circuits
- Types of circuits
- Series
- One circuit total
- All devices must be connected and on for all to work
- This is because the devices complete the circuit
- As devices are added the current goes down because they are each taking away from he same amount of power
- Fuses and circuit breakers are wired in series so they cant cut the entire system off when the current is too high
- Parallel
- Independent circuits within the entire system
- Devices can be disconnected and others will still work
- Most houses are wired in parallel
- Current goes up and resistance goes down as more devices are added to the circuit
- Fuses and Circuits prevent fires because parallel circuits can get hot as more devices are added
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