1. Electricity Unit

2. What is electricity? Electricity is the movement of electrons through something (“medium”) Electrons move for 2 reasons – They are attracted to… PROTONS! – They are “hit” by another electron and bounce out of the way.

3. What is a circuit? A complete pathway for electrons to travel – In a complete circuit, electrons must be able to travel back to their starting point!

4. Has 3 main parts: – Source of electrons (ie. battery) – Medium for electrons to travel (ie. wire and other conductors) – Something for electrons to do work on (ie. light bulb)

5. Can have other parts – Resistor- designed to slow down the flow of electrons » Made of material that isn’t quite considered to be a conductor, but isn’t an insulator either…. » Different materials allow circuits to have different resistances.

6. – Switch- allows you to disconnect the circuit when you want electrons to stop flowing and reconnect when you want electrons to resume flowing

7. Circuits are often drawn as a diagram using the symbols given below:

8. What are some “types” of circuits? Complete vs. Incomplete Pathway Closed circuit Just means the circuit is complete and electricity CAN travel thru it.

9. Open Circuit – Means the circuit is incomplete and electricity CANNOT travel thru it. – Usually, this occurs when you move a switch to the off position.

10. Organization of Pathway Series Circuit – All the objects that work is done on (ie. light bulb) are in a straight path. – In a series circuit, you can travel from one object to the next only ONE way. There are no options!

11. Parallel Circuit – Objects that work is done on (ie. light bulb) are NOT in straight path. – In a parallel circuit, you have options as to how you can travel from one object to the next!

13. What is an electrical current? Electrons in motion Comparison to water hose: this is the moving water

14. How is current measured? Current is measured in terms of the rate at which electrons travel In an equation, current is symbolized by I Units: amperes or amps (A).

15. Tool Used to Measure: Ammeter Comparison to water hose: this is like if you sat in one spot and counted how many water molecules passed you in a certain amount of time

16. Two Main Types of Current – Alternating (AC): electrons constantly change directions, like an outlet – Direct (DC): electrons move only in one direction, like a battery

17. What is voltage? Voltage is a measure of the amount of force that keeps the electrons flowing. In an equation, voltage has the symbol V Units: Volts (V). – The voltage of a typical small battery is 1.5 V. The voltage of a typical car battery is 12 V.

18. Tool Used to Measure: Voltmeter Comparison to water hose: this is like the water pressure.

19. What is resistance? The amount of resistance present tells us how much the flow (current) is restricted by the material (resistor) – Resistance is caused by friction. In an equation, resistance is symbolized by R.

20. Units: Ohms (Ω) Comparison to water hose: this is like squeezing the hose in one spot.

21. How are all of these related? Ohms Law: The current thru a circuit (I) is directly related to the force keeping the electrons flowing (V) and inversely related to the resistance (R) present in the circuit. Equation: I = V/R Units: I in amps, V in volts, R in ohms.

22. What is electrical power? Electrical power is the rate at which electrical work is done and is also called power rating. – Electrical power is the energy associated with electrical charges, whether moving or at rest. – The symbol for electrical power is P. The unit of measure for electric power is watts and the symbol for watts is W

23. Electric power can be calculated by multiplying the total current (I) in a circuit and the total voltage (V) across a circuit. Formula – Electric power - P= current x voltage = IV

24. What happens when a current has too much power? When the resistance of a circuit is too low, the wires carry too much current. When this happens, the circuit is said to be overloaded. – Circuits can be overloaded when too many appliances are plugged into a single power source.

25. There are two ways to prevent overloading circuits: – Fuse A fuse is an electrical device contains a metal strip that melts (thus opening the circuit) when the current in a circuit becomes too great. Once the metal strip inside a fuse melts, it must be replaced.

26. – Circuit breaker A circuit breaker is a device that protects a circuit from current overloads by opening the circuit when the current becomes too great. Circuit breaker act like switches and can be reset to close the circuit again.

27. What is a short circuit? Caused by improper wiring. The current travels around the resistor, therefore overloading the circuit.

28. Why do we shock people? When you walk across the floor, electric charges are moving from the floor through your body, causing an excess of electrons in your body. When you come in contact with something that doesn’t have an excess of charge, the charges move from your body to the other thing.

29. Called static electricity. – “Static”- means unmoving. The electrons just hang out in your body for a while.

30. What’s a Coulomb? A coulomb is a way to tell the amount of charge in an object. 1 Coulomb = 6.241506×10 18 electrons Coulomb's Law is one of the basic ideas of electricity in physics. The law looks at the forces between two charge objects.

31. Tells us 2 things: 1)As distance increases, the force between the two objects decreases.

32. The force between the objects can be positive or negative depending on whether the objects are attracted to each other or repulsed.

33. F=kq 1 q 2 /r 2 - It looks scary, but think of Newton’s law of gravitation - F = G m 1 m 2 / d 2 – F = force – k = constant – q = charge of objects (1 and 2) – r = distance between them