Chapter 5: Electrical currents

1. Chapter 5: Electrical currents • What is electricity? http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/electricityintro.htm

2. Electric Charge • Do you remember how ions form in chemistry? • Ions form when atoms gain or lose electrons. To acquire their charge, positive ions lose electrons and negative ions gain electrons. • If electrons are lost to another atom, then an atom would become positively charged. • If electrons are gained from another atom, then an atom would become negatively charged.

3. What do an apple and a battery have in common?

4. Electricity is a form of energy (electrical) producedby the movement of electrons. The electrons of some atoms, like those of copper and other metals, are only loosely attached, which allows electricity to travel through these materials easily. These types of materials are known as “conductors.” An outside force—such as light, heat, pressure, or a chemical reaction—can cause electrons to break free and get “bumped” from one atom to the next. A sequence of electrons then passes from atom to atom. This continuous flow of electrons from atom to atom through a conductor is called electric current.

5. Electrons can be made to move from one atom to another. When those electrons move between the atoms, a current of electricity is created. The electrons move from one atom to another in a "flow." One electron is attached and another electron is lost. Since all atoms want to be balanced, the atom that has been "unbalanced" will look for a free electron to fill the place of the missing one. We say that this unbalanced atom has a "positive charge" (+) because it has too many protons. Since it got kicked off, the free electron moves around waiting for an unbalanced atom to give it a home. The free electron charge is negative, and has no proton to balance it out, so we say that it has a "negative charge" (-).

6. Electric Charge • Charges that are the same repel each other. Charges that are different attract each other.

7. Electric Force • An electric field is a region around a charged object where the object’s electric force is exerted on other charged objects.

8. Electric Force • An electric field is a region around a charged object where the object’s electric force is exerted on other charged objects.

9. Transferring Charge • There are three methods by which charges can be transferred to build up static electricity: charging by friction, by conduction, and by induction.

10. Transferring Charge • There are three methods by which charges can be transferred to build up static electricity: charging by friction, by conduction, and by induction.

11. What is Induction? • When a substance gains a charge without touching another substance, it is said to have gained its charge through induction. • Example: you are about to touch a door knob and you get shocked!!!!!

12. Quick Quiz • What happens when you get shocked by static electricity? • A. Electrons are transferred from one object to another. • B. Protons are transferred from one object to another. • C. Neutrons are transferred from one object to another. • D. Positrons are transferred from one object to another.

13. Quick Quiz • What happens when you get shocked by static electricity? • A. Electrons are transferred from one object to another. • B. Protons are transferred from one object to another. • C. Neutrons are transferred from one object to another. • D. Positrons are transferred from one object to another.

14. Types of Current • There are two types of current: direct current (DC) and alternating current (AC). • Batteries provide DC voltage to an object. There are several types of batteries such as AAA, AA, C, D, 9 Volt. Of these batteries, the 9 Volt provides the most voltage and the D has the greatest amount of stored energy in it. • Alternating current (AC) is a type of electric current you find in your home. Alternating current is a flow of electric current that will regularly reverse its direction. The electric current can flow forwards and backwards!

15. Flow of Electric Charges • Electric current is the continuous flow of electric charges through a material.

16. What is the difference between staticelectricity and electrical current? Static electricity is stationary or collects on the surface of an object, whereas electrical current is flowing very rapidly through a conductor. The flow of electricity in electrical current has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage. Water pressure and voltage behave in similar ways.

18. The pressure of the water flowing through the water pipes is analogized to the voltage (electric potential or potential difference) flowing through the terminals or wires of the circuit. Electric Potential Energy, (or Electric Potential or Potential or EMF – Electromotive Force) is defined as the amount of work done for each unit of charge. Therefore, V= W/q where W is the amount of work done or energy required, q is amount of charge. The unit used to measure voltage is volts (V). 1 Volt = 1 Joule per Coulomb

19. Current and Electrical Potential When a battery is connected to a conductor one end of the conductor becomes positively charged and the other end becomes negatively charged. This sets up an electric field along the length of the conductor. As a result, the mobile charges (electrons in a wire for example) will move along the conductor. We call this movement of charge along a conductor an electric current.

20. One coulomb of charge is equal to 6.242 × 1018 elementary charges. One elementary charge is equal to 1.602 × 10−19 C.

25. Electron Flow http://mste.illinois.edu/users/Murphy/HoleFlow/default.html Direction of Current Find out why current is usually shown from positive to negative. http://mste.illinois.edu/users/Murphy/HoleFlow/ElectricFluid.html Find out why this isn't quite as backwards as it seems. Hole Flow http://mste.illinois.edu/users/Murphy/HoleFlow/HoleFlow.html

29. Potential Difference When a battery, or other source of potential, is connected in a circuit, it produces a potential difference; that is, a difference in the potential energy of the charges in the conductors connected to its terminals.

32. An Electric Circuit • An electric circuit is a complete, unbroken path through which electric charges can flow.

33. Conductors vs Insulators • Electricity is conducted through some materials better than others. Resistance measures how well a material conducts electricity. Rubber, plastic, cloth, glass and dry air are good insulators and have very high resistance that does not allow electrons to move through them very well. • Most metals - like copper, aluminium or steel - are good conductors that allow electrons to flow through them.

34. Resistance • Two factors that affect the resistance of water flowing in a pipe are diameter and length. Similarly, the diameter and length of a wire also affect resistance in a circuit.

35. Ohm’s Law Georg Ohms • Increasing voltage increases the current • Increasing the resistance will decrease the current (if voltage is held constant). • The relationship between voltage and current is a directly proportional. This means that as one variable increases, the other increases (or as one decreases, the other decreases). • The relationship between current and resistance is inversely proportional. This means as one variable increases, the other decreases and vice versa.

36. Electrical Equations Voltage = Volts Current = Amps Resistance = Ohms Volts = joules/coulomb Amperes = coulombs/second Voltage = Current x Resistance Current = Voltage ÷ ResistanceResistance = Voltage ÷ Current

39. Current vs Voltage Graphs Notice the relationship between current and voltage in the middle graph.

40. Use graphs to read of values. Use Ohm’s Law at a point. Non-ohmic Conductors What is the resistance of the above circuit at 240V?

41. Resistivity