1. Exam Review Electricity

2. Electric Charges An electric charge is a negative or a positive amount of electricity that builds up in an object. Electrons have a negative charge and protons have a positive charge. Like charges attract, opposite charges repel.

3. Charged Objects Objects become negatively charged when they have an excess of electrons. Objects become positively charged when they have lost electrons. Protons are never lost or gained.

4. Neutral Objects Neutral objects have the same number of positive and negative charges. The positive charges in one neutral object will attract the negative charges in another object.

5. Static Electricity Static electricity is a charge on a substance that stays in the same place. Electrostatics is the study of static electric charge.

6. Conductors and Insulators Conductors allow electrons to move freely throughout them. They carry, conduct or transmit electricity. –Ex: Silver, gold, copper wires Insulators hold their electrons very tightly. They do not conduct electricity. –Ex: Rubber, fur, glass

7. How Lightning is Produced Strong winds and the collisions of water droplets and ice particles in the clouds strip electrons from some particles and deposit them on others. Negative charges collect at the bottom of the cloud. The higher parts of the cloud are colder and positively charged.

8. The negatively charges on the bottom of the cloud repel electrons on the surface of the Earth, leaving the ground positively charged just below the cloud. The strong attraction between the negative cloud and the positive ground pull electrons off atoms and molecules in the air.

9. Once a chain of ions forms, a giant discharge occurs between the cloud and the ground. Electrons crash through the air so fast, colliding with other molecules, heating and lighting up the air.

10. Current Electricity Current electricity is a continuous flow of electric charge. For example: When we hook something up to a battery, the electrical current flows through a path called a circuit.

11. Circuit Measurements Electric Current - Flow of electrons through a material. –Measured as the amount of current that passes a conducting wire every second. Electrical Potential – –Stored electric energy

12. Moving Charges The symbol for current is I and the symbol for charge is Q, t is used to represent time. Current = charge moving past a point time I = Q t

13. Charge (Q) is measured in Coulombs (C) Current (I) is measured in Amperes (A) Time (t) is measured in seconds (s)

14. Voltage Voltage – causes current to flow through an electrical circuit Volt – unit of measure to measure the potential difference A Voltage Source (battery or generator) is required to maintain the electrical potential in a circuit.

15. Electrical Current Electric current is a measure of the rate at which the electric charges move past a given point in a circuit. Electrical Current is measured in Amperes (A)

16. Measuring Electricity Electric Potential – the electrical energy that an electron possesses. Current is measured by an Ammeter Voltage is measured by a Voltmeter

17. Resistance Amount of Electrical Current ( amps) depends on more than just Voltage, it depends on the Resistance found in the circuit.

18. Resistance Resistance – is the ability to hold back the flow of electrons in a conductor. The molecules found in every type of conductor resists the flow of electrons to some extent.

19. When electrons flow through a conductor the electrical resistance causes a loss of electric potential (voltage). There is a “difference” in the amount of electric potential after the electrons have flowed through the conductor. This difference is referred to as the potential difference.

20. Ohm’s Law The potential difference between two points on a conductor is proportional (directly related) to the electric current flowing through the conductor.

21. Potential = Electric Current x Electrical Resistance Difference (Voltage Drop) V = I x R Potential difference (V) is measured in volts (V) Electric Current (I) is measured in ampere (A) Resistance (R) is measured in ohms (  ) Ohm’s Law

22. Circuits Electric Circuit – a controlled path in which electric current passes through. Electric circuits are used to convert electrical energy into other forms of energy such as heat or light. We can use a circuit diagram to show the path of the electric current.

23. Parts of a Circuit 1. Source of electrical Energy – the place or thing that generates the electrical energy. 2. Electrical Load – anything that converts electrical energy into the form of energy needed.

24. 3.Electric Circuit Control Device – a switch that controls the electricity (turn on and off). 4. Connectors – the conducting wires that provide the controlled path for electric current to flow to each part of the circuit.

25. Movement in a Circuit The movement in a circuit is continuous and controlled. A battery serves as a source of energy for a circuit. The electrical energy stored in the battery is called electrical potential energy. The electrons have the potential for doing work but are unable to do it until the battery is connected to the load and the circuit is closed.

26. Closed Circuit – a circuit that is “on” or allowing electricity to flow through. Open Circuit – a circuit that is “off” or not allowing electricity to flow through.

27. Types of Circuits There are 2 types of circuits: –Series Circuit: A circuit with only one path for current to flow –Parallel Circuit: A circuit with many pathways for current to flow.

28. Series Circuits In a series circuit electrons travel around one closed loop. The current at any one point in a series is exactly the same as the current at any other point. The charges pass from one load to the next before returning to the power source to be energized again.

29. Series Circuit

30. Parallel Circuits In a parallel circuit charges flow around two or more different loops. After leaving the power source they eventually reach a “fork in the road”. Some charges take one path while other charges take another path. The current in a parallel circuit is not the same at every point in the circuit.

31. Parallel Circuits