3. 1. 2. All matter is composed of atoms, which have a + charged nucleus surrounded by – charged electrons. All electrons are identical in mass and charge. All protons are identical as well.

4. 3. 4. Protons and electrons have equal but opposite charges. Atoms usually have as many electrons as protons, so the atom has zero NET charge.

5. * Matter becomes charged when atoms either gain or lose electrons. If an atom gains one or more electrons the atom acquires a NET (-) charge, while if an atom loses one or more electrons the atom acquires a NET (+) charge.

6. * When matter becomes charged no electrons are created or destroyed. Electrons are simply transferred from one material to another. Charge is conserved. Example: Electrons are transferred from the fur to the rod. The rod is then negatively charged. Is the fur charged? How much compared to the rod? Positively or Negatively? Yes Equal in magnitude Positively

7. * Like charges exert repulsive (pushing) forces, while unlike charges exert attractive (pulling) forces.

8. * Vectors can be used to show the electrical force acting between charged objects. Each vector represents a force being applied to the charged object by another charged object. * In relationship to gravitational forces, electrical forces are very, very strong.

9. * One coulomb (C) is the charge of 6.25 x 10 18 electrons. The charge that produces a lightning bolt is about 10 C. The magnitude of the charge of an electron is called the elementary charge (1.60 x 10 -19 C).

10. F = k q 1 q 2 d2d2 * The electrical force between two charged objects decreases inversely as the square of the distance between them. Electrical Force Proportionality Constant (9.0 x 10 9 N m 2 /C 2 ) dd Distance Charge #1 Charge #2

11. Question: Calculate the force exerted upon one electron by another. Known:.01 m q 1 =1.60 x 10 -19 C q 2 =1.60 x 10 -19 C d =.01 m k =9.0 x 10 9 N m 2 /C 2 F = k q 1 q 2 d2d2 F = ( 9.0 x 10 9 N m 2 /C 2 ) ( 1.60 x 10 -19 C) (1.60 x 10 -19 C) (.01m) 2 F = 2.3 x 10 -24 N

12. Conductors are materials (typically metals) that exhibit loose valence electrons in their outer shells. For this reason metals allow electrical currents and heat to pass through them easily. Insulators (like rubber and glass) are materials that have tightly bound valence electrons. The electrons are NOT free to wander about among other atoms in the material. These materials are poor conductors of heat and electricity.

13. * Electrons can be transferred by friction when one material rubs against another. This method of charging is called charging by contact.

14. * Charging by contact occurs because not all materials are composed of the same atoms. Different atoms have different affinities for electrons. Wool atoms have a higher affinity for electrons than nylon atoms. While PVC has a higher affinity for electrons than wool atoms.

15. * Charging by conduction can be seen with an electroscope. If you touch a charged object to an electroscope the metal arms near the base will repel one another, as seen in the animations to the left.

16. * Charging by induction occurs without physical contact. If you bring a charged object near a conducting surface, you will cause electrons to move in the surface material even though there is no physical contact. a.) Each sphere is uncharged (Net charge of “0”). b.) A negatively charged rod is brought close to the spheres which repels the electrons within the spheres. c.) The spheres are separated, leaving them with a imbalance of charge. d.) The spheres have acquired a charge without any contact with another charged object.

17. Electrons are able to move from one atom to another within the conductor.

18. * We can charge a single sphere by induction if we touch it when different parts of it are differently charged. a.) Net charge on the metal ball is zero. b.) Charge redistribution is induced on the ball by the presence of a charged rod. c.) Touching the negative side of the ball removes electrons by contact. d.) This leaves the ball positively charged.

19. * Charging by induction is not restricted to conductors. When a charged object (balloon) is brought near an insulator (wall), there are no free electrons that can migrate throughout the insulating material. Instead, there is a rearrangement of charges within the atoms and molecules themselves. a.An un-polarized atom b.An atom that has been electrically polarized (the electron cloud has shifted due to an external force).

20. Electrons only rearrange themselves within the atoms of the insulator.

21. * Upon rubbing, the balloon strips electrons from the man’s hair (charging by contact). The now negatively charged balloon causes the atoms in the wall to become electrically polarized (charging by induction). The balloon and wall exert an attractive force on each other (opposites attract).

22. * Charging by induction can be seen with an electroscope. If you bring a charged object close to an electroscope the metal arms near the base will repel one another, as seen in the animations to the left.

23. Charging by induction occurs during thunderstorms. The negatively charged bottoms of clouds induce a positive charge on the surface of the Earth below. Lightning is an electrical discharge between a cloud and the oppositely charged ground. *

25. The space around every electric charge is filled with what is called an electric field. An electric field is a kind of aura that extends through space. The picture above shows a positively charged particle and the electric field that surrounds it. The different sized arrows represent the electrical force that would affect another positively charged particle. Why are the arrows of different size?

26. An electric field is present in any region where a charged object experiences an electric force. The only way we can tell if a field exists is to place a test charge at that spot and see if it feels a force. The animation to the left shows a stationary charge. When a test charge is brought in, a force is present on that charge and so it shows evidence of a field being present. The closer the test charge is brought to the stationary charge the greater the force.

27. E = F on q q Electric Field Force on Test Charge Magnitude of test charge A positive test charge of 5.0 x 10 -4 C is in an electric field that exerts a force of 2.5 x 10 -4 N on it. What is the magnitude of the electric field at the location of the test charge? E = F q = 2.5 x 10 -4 N 5.0 x 10 -4 C =.5 N/C

28. A positive test charge, of unknown magnitude, is placed in an electric field at a position where the field has a magnitude of 2.0 N/C. If the force exerted by the field on the test charge is 5.0 x 10 -6 N, calculate the magnitude of the test charge. Known E = 2.0 N/C F = 5.0 x 10 -6 N Unknown q E = F q 2.0 N/C = 5.0 x 10 -6 N q q = 2.5 x 10 -6 C

29. For isolated charges, as seen above, the lines that represent the electric field extend to infinity. However, when placing opposite charges next to one another, we represent the lines as emanating from the positive charge and terminating on the negative charge. Can you picture what the lines would look like if both charges were negative or positive?

30. The illustration below shows the path that a positively charged particle would take when traveling through the electric field produced between oppositely charged particles.

31. Like Charges (2 positives, or 2 negatives) Opposite Charges (1 positive 1 negative)

32. PE = mgh Recall that objects have energy due to their position away from the earth. This energy is called gravitational potential energy. The amount of PE is directly related to the object’s mass and distance from the earth. In a similar way, a charged object can have potential energy by virtue of its location in an electric field. The electric potential energy of a charged object is increased when work is done to pull or push it against the electric field of another charged object.

33. In order to bring two like charges near each other work must be done. In order to separate two opposite charges work must be done. As the monkey does work on the positive charge, he increases the energy of that charge. The closer he brings it, the more electrical potential energy it has. If he brought 2 or 3 charges instead of one, then he would have had to do more work in turn creating more electrical potential energy. So, the amount of electrical potential energy is directly related to the amount of work done on a charged object.

34. Potential difference, also called electrical potential, is defined as the amount of electrical potential energy per unit of charge. In this example the amount of work done by the person is 30 J, this is also the amount of electrical potential energy that is possessed by all three charges together. The electrical potential is the amount of energy per unit of charge. Electrical Potential = work or  electrical potential energy unit of charged moved V = W q moved = 30 J 3 C = 10 J/COr 10 Volts

35. Keep in mind that the electrical potential describes the amount of energy per unit of charge. This means that when one of the charges is released, the electric field will do 10 Joules of work on the charge so it will have a kinetic energy of 10 Joules the instant before it strikes the negative charge. 1 Volt = 1 Joule 1 coulomb

36. E = F q V = Fd q V = Ed Electric FieldPotential Diff. A second equation for potential diff. In a uniform (unchanging) electric field, the amount of potential difference (voltage) between two opposite charges is directly related to the distance between them. A new equation for potential difference can now be derived. The potential difference between two points in a uniform electric field is the product of the magnitude of the electric field and the distance between the charges.

37. * A good analogy for a battery is a cafeteria. When a college student needs energy he will enter a cafeteria. While in the cafeteria, he will eat, which in turn causes him to have more potential energy. When leaving the cafeteria he has more potential energy than he had upon entering. Resistor + - e - (1.6 x 10 - 19 C) e-e- e-e- e-e- Transfer of Energy (electrical potential to Heat and Light) e-e- Electrical Potential Energy is increased 6 Volt Battery ( Every coulomb of charge gains 6 joules of energy) e-e-

38. A coulomb of charge in a 1.5 volt “D-Cell battery or a 1.5 volt “AA- Cell” battery will do 1.5 joules worth of work moving from the positive to the negative terminal. The difference between the D-cell and the AA-cell is that the D-cell has more Coulombs worth of charge, so it will last longer. The AA-cell may only light a light bulb for 15 minutes while a D-cell may keep the same bulb lit for several hours. As a result of having more charge, the D- cell has more energy and can do more work, but it will still do work at the same rate.

39. All capacitors are made up of two conductors separated by an insulator. The capacitor to the left is simply two conducting sheets of metal separated by air. Electrical energy can be stored in a capacitor. The storage of energy in a capacitor is similar to a dam. Charges build- up on one of the metal plates, just as water builds up on one side of a dam. A charged capacitor is discharged when a conducting path is provided between the plates.

40. Each key of the keyboard is part of a capacitor. When depressed, capacitor plates are pushed together to allow for charges to flow. This in turn sends signals to the computer.

41. * Current electricity is simply the movement of charge from an area of high potential to an area of lower potential through a conducting material. The flow of charge will exist as long as there is a potential difference and a conducting path.

42. * Any path along which electrons can flow is a circuit. For a continuous flow of electrons, there must be a complete circuit with no gaps. Most circuits have more than one device that receives electric energy. These devices are commonly connected in a circuit in one of two ways, series or parallel.

43. *A series circuit can be defined as a single path for which electrical charges can follow. *Electrical Current is defined as the amount of charge (coulomb) that passes a certain point in a certain amount of time (second). 5 C in 1 second = 5 amps * Current is the rate of flow of electric charge. In an equation it is represented by the letter (I). The unit for current is C/s or amps.

44. * Resistance is a measurement of how easily electrical charge can move from one point in a circuit to another point. * The less conductive a substance is the more resistant it will be to charge flow. * Resistors are objects that transform electrical potential energy into some other form of energy. Example: Light Bulb –transforms electrical potential energy into heat energy and light energy. * Conductive wires are slightly resistant to charge flow. The thicker the wire the better the flow of charge, as seen with the picture to the left.

45. * Resistance [R] is measured in units called ohms (  ). * As the diameter of a wire increases so does the current, due to the fact that there are more coulombs of charge present in a given area. * For most conductors, increased temperature means increased resistance.

46. * Electrical power is defined as the amount of electrical potential energy that is transformed into another form of energy, by a resistor (ie. Lightbulb), each second. Power = Voltage x Current J/C C/s J/s Watts The power of a light bulb that is in a circuit with 2.0 amps of current and 6.0 volts of potential difference will display how much power ? P = V I P = 6.0 Volts x 2.0 Amps P = 12 watts

47. I = V R * The relationship among voltage, current, and resistance is summarized by a statement called Ohm’s law. Ohm discovered that the current in a circuit is directly proportional to the voltage established across the circuit, and inversely proportional to the resistance of the circuit. Current = Voltage resistance or Determine the amount of current present in a circuit that has a 3 V battery attached in series with a 1.5  light bulb. I = 3 V = 2 amps 1.5 

48. R total = R 1st resistor + R 2nd resistor + ………… * The overall resistance in a series circuit is equal to the sum of the individual values of each resistor. As more and more resistance is added to the circuit the current will drop.

49. Voltage Rise battery = Voltage Drop resistor #1 + Voltage Drop resistor #2 + …… *The total voltage impressed across a series circuit divides among the individual electrical devices in the circuit so that the sum of the voltage drops across each individual device is equal to the total voltage supplied by the source. Notice from the animation that the voltage drop across each device is proportional to its resistance. This implies that more energy is needed to move a charge through a larger resistance (Ohm’s Law).

50. This 100 watt light bulb when plugged into a standard 120 volt outlet will draw a current of.83 amps (I = P/V). A 50 watt light bulb when plugged into the same 120 volt outlet will draw a current of.416 amps (I = P/V). From ohm’s law (R = V/I), we can see that the 50 watt light bulb has a higher resistance than the 100 watt light bulb.

52. A parallel circuit allows more than one path for charge to follow. As can be seen in the pictures below, a break in one path does not lead to a stoppage of current in the other paths. This occurrence is the advantage of a parallel circuit.

53. 1. The voltage drop across any resistor is the same as the voltage rise. 2. The amount of current in each branch is inversely proportional to the resistance of the branch. (I = V/R, Ohm’s law applies separately to each branch.) 30 volts I = 30 V / 30  I = 1 amp I = 30 V / 10  I = 3 amps 3. The total current in the circuit equals the sum of the currents in its parallel branches. I total = I 1 + I 2 + ……. 4. As the # of branches is increased, the overall resistance of the circuit is decreased. 4 amps

54. 1. A parallel circuit contains more than one path for coulombs of charge to follow when traveling through a circuit. 2. The voltage rise of a parallel circuit is equal to the voltage drop of each individual branch within the circuit.

55. 3. The overall current within a parallel circuit is equal to the sum of the individual branches’ currents. I total = I 1 + I 2 + …………

56. 4. You can find the total resistance of a parallel circuit using the following equation: 1 = 1 + 1 + ……….. R total R 1 R 2 5. If one branch of a parallel circuit is open the other branches of the circuit will still be operate. The overall functioning of the circuit does not stop if there is a break within one of the branches.