Electric Charge and Force A. Electric Charge

1. Electric Charge and Force A. Electric Charge

2. 1. Type of Charges positive negative neutral (lack of charge)

3. 2. Source of charge: The Atom All matter is made up of atoms. Each atom contain a central "nucleus". The nucleus contains protons and neutrons, and the nucleus is considered to be at rest. Electrons move around the nucleus in the empty space of the atom. In a nuetral atom, the number of protons equal the number of electrons

4. a. Atomic Structure Protons and electrons have equal and opposite electric charge. By convention, electrons are said to have a negative charge. Similarly, protons are said to have a positive charge. Neutrons have no charge. Atoms are electrically neutral...not because they contain no overall charge...they have equal numbers of protons and electrons...their total charge adds up to zero.

5. Electric Forces • Like charges repel, unlike charges attract • Two electrons will tend to repel each other because both have a negative electrical charge. • Two protons will also tend to repel each other because they both have a positive charge. • Electrons and protons will be attracted to each other because of their unlike charges. • Since the electron is much smaller and lighter than a proton, when they are attracted to each other due to their unlike charges, the electron usually does most of the moving. • This is because the protons have more mass and are harder to get moving. Although electrons are very small, their negative electrical charges are still quite strong. • Another important fact about the electrical charges of protons and electrons is that the farther away they are from each other, the less force their electric fields have on each other. Similarly, the closer they are to each other, the more force they will experience from each other due to this invisible force field called an electric field.

6. Like energy and momentum, charge is neither created nor destroyed, it is conserved. Opposite charges attract and like charges repel. As a result negatively charged electrons are attracted to the positive nucleus An electron is said to have a charge of - and a proton a charge of +.

7. 1 An atom in it's normal state has no charge. This is due to the fact that atoms A have only neutrons B have no protons or electrons C have equal numbers of protons and electrons answer C

8. 2 What object moves freely around the atom? A Electron B Neutron C Proton D Nucleus answer A

9. 3 What symbol is used for the charge on a proton? A + B - o C answer A

10. What the atom DOESNT look like: This is NOT what an atom looks like!!! If an atom was magnified so that the nucleus was the size of a dime on the 50 yard line of a football field, the first electrons would be at the edge of the stadium…nothing exists in between. The remaining electrons could be miles away (depending on the element/size of the atom) And the electrons would STILL be too small to see. Atoms are almost all empty space. Since everything (including us) is made of atoms, that means everything (including us) is mostly empty space.

11. More on Electrons The nuclei of atoms are much more massive than electrons. Each proton or neutron is 2000 times more massive than an electron with each nucleus containing at least one proton. That's one reason that when electric charge moves it's usually the result of electrons moving, not protons. The other reason is that in solids, the nuclei are locked together so they can't move...regardless of their mass.

12. b. ions Some atoms are charged because they have more protons or electrons----- When that happens----the atom gains a charge and is called an “ion” Ions are atoms with charges

13. b. ions Some atoms are charged because they have more protons or electrons----- When that happens----the atom gains a charge and is called an “ion” Ions are atoms with charges

14. 3. Build up of Charge Solids are a form of matter whose nuclei form a fixed structure. Nuclei, and their protons, are "locked" into position. Some electrons are bound more tightly to their atoms than other electrons. It depends on the make up of the material. For example, human hair easily gives up electrons while plastic is good at “stealing” electrons. Static electricity occurs when material obtains and holds onto a charge (either positive or negative)

15. 4. Movement of Charge A nucleus, and the protons, are "locked" into position. Protons are never removed or added to atoms (unless we are working in the field of nuclear physics—not this unit) In solids…. Some materials have electrons that are bound more tightly to their atoms than other electrons. In other materials, electrons are free to move. In conductors, some electrons are free to move through the solid. In insulators, no electrons are free to move Current electricity is the movement of charges through a conductor in a particular direction (like a flow of water) Static electricity is the build up of charges on material without “flowing”

16. a. Conductors In conductors, electrons move freely inside the solid. Like charges repel, therefore the electrons tend to want to spread as far apart as possible.

17. b. Insulators Insulators are materials that have strongly bound electrons which cannot move within the solid. Different insulators have varying levels of insulation capabilities. However, electrons can still be picked up or removed from the material (just can’t move with in it)

18. c. electrolytes Electrolytes are liquids that conduct electricity. Most often, water has charged partilces dissolved in it. These charge can move through the water to conduct. Water itself is an insulator. (pure water does not conduct, tap water does)

19. II. Electrical Potential Difference A. Movement of Charges • Like charges repel and opposite charges attract • Repulsion and attraction are forces that cause charges to move • Force causing motion over a distance is known as ___________ which can be converted into ___________. • Which way will charges move?….

20. B. Electrical Potential Placing a positive charge near a negative charge is a form of potential energy. They want to move toward each other. It takes work to keep them apart. Like charges desperately want to move away from each other. It takes work to keep them together. A force needs to separate opposite charges and a force needs to keep like charges together. Charges that are forces to be apart are together contain potential energy (think of GPE or EPE). The amount of potential energy per charge is called electrical potential

21. C. Potential Difference (voltage) Two charges separate from each other will move. Like charges move away from each other Opposite charges move towards each others The difference in the potential energy they have from before and after the movement is the potential difference, which we call voltage Charges are being forced to stay close to each other When free to move the charges will separate and each have less potential energy When free to move the charges will separate and each have less potential energy Each charge has less potential energy They want to separate; right now they have potential energy Each charge has high potential energy The difference is potential energy for each charge before and after the move is called Potential Difference, or Voltage and is measured in volts.

22. III. Current A. Definition Current is the movement of charges in a single path; it measures the number of charges that flow past a point in a given time (C/s—renamed amperes) This requires a conducting path (a metal wires)

23. III. Current B. Cause of current Charges that are separated or put near each other have electrical potential energy Charges move through a wire to go from high potential energy to low potential energy: which is voltage

24. III. Current C. Factors Affecting Current • Resistance • Defined: resistance is hindrance to the flow of electricity • Factors affecting resistance • Diameter of a wire (the greater the diameter, the lower the resistivity) • Length (the longer the wires, the more the resistance) • Temperature (generally, higher temp is lower conductivity) • Type of material (varies)

25. Current C. Factors Affecting Current • Ohm’s Law

26. Current The letter "I" is the symbol for current. It is defined as the amount of charge that flows past a location in a conductor per unit time. Current flows through a conductor It is measured in amperes (amps or A)

27. Voltage The letter “V" is the symbol for voltage. It is defined as the is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit. Batteries and outlets provide the force that pushes the electrons through the conductor It is measured in volts (V)

28. Batteries D, C, AA, & AAA have the same voltage, however they differ in the amount of power they deliver. (meaning how fast) For instance, D batteries can deliver more current and therefore more power. 9 V D AA C AAA 1.5 V

29. Resistance The letter “R" is the symbol for resistance. Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow Appliances are filled with resistors It is measured in ohms (Ω)

30. What is Ohm's Law: Ohm's shows the relationship between electric voltage, current and resistance. What is voltage? An analogy would be a huge water tank filled with thousands of gallons of water high on a hill. The difference between the pressure of water in the tank and the water that comes out of a pipe connected at the bottom leading to a faucet is determined by the size of the pipe and the size of the outlet of the faucet. This difference of pressure between the two can be thought of as potential Voltage.What is current? An analogy would be the amount of flow determined by the pressure (voltage) of the water thru the pipes leading to a faucet. The term current refers to the quantity, volume or intensity of electrical flow, as opposed to voltage, which refers to the force or "pressure" causing the current flow. What is resistance? An analogy would be the size of the water pipes and the size of the faucet. The larger the pipe and the faucet (less resistance), the more water that comes out! The smaller the pipe and faucet, (more resistance), the less water that comes out! This can be thought of as resistance to the flow of the water current. All three of these: voltage, current and resistance directly interact in Ohm's law.Change any two of them and you effect the third.

31. Current, Resistance & Voltage Raising resistance reduces current. Raising voltage increases current. We can combine these relationships in what we call "Ohm's Law". Another way to write this is that: OR V = IR V R I =

32. IV. Circuits A. Definition • In electronics, a circuit is a path between two or more points along which an electrical current can be carried.

33. IV. Circuits B. Parts Drawing realistic pictures of circuits can be very difficult. For this reason, we have common symbols to represent each piece. Wire Switch Resistor Battery Bulb *Note: Circuit diagrams do not show where each part is physically located.

34. IV. Circuits C. Types of circuits 1. Series • In series circuits, current can only take one path. • The amount of current is the same at all points in a series circuit.

35. Resistance in a series circuit • Each resistance in a series circuit adds to the total resistance of the circuit. Rtotal = R1 + R2 + R3... Total resistance (ohms) Individual resistances (W)

36. Light bulbs, resistors, motors, and heaters usually have much greater resistance than wires and batteries.

37. Voltage in a series circuit • Each separate resistance creates a voltage drop as the current passes through. • As current flows along a series circuit, each type of resistor transforms some of the electrical energy into another form of energy • Ohm’s law is used to calculate the voltage drop across each resistor.

39. IV. Circuits C. Types of circuits 2. Parallel • In parallel circuits the current can take more than one path. • Because there are multiple branches, the current is not the same at all points in a parallel circuit.

40. Sometimes these paths are called branches. • The current through a branch is also called the branch current. • When analyzing a parallel circuit, remember that the current always has to go somewhere. • The total current in the circuit is the sum of the currents in all the branches. • At every branch point the current flowing out must equal the current flowing in. • This rule is known as Kirchhoff’s current law.

42. Voltage and currentin a parallel circuit • In a parallel circuit the voltageis the same across each branch because each branch has a low resistance path back to the battery. • The amount of current in each branch in a parallel circuit is notnecessarily the same. • The resistance in each branch determines the current in that branch.

43. Advantages of parallel circuits Parallel circuits have two big advantages over series circuits: • Each device in the circuit sees the full battery voltage. • Each device in the circuit may be turned off independently without stopping the current flowing to other devices in the circuit.

44. Calculate current • Two bulbs with different resistances are connected in parallel to batteries with a total voltage of 3 volts. • Calculate the total current supplied by the battery.

46. Adding resistance in parallel circuits • A circuit contains a 2 ohm resistor and a 4 ohm resistor in parallel. • Calculate the total resistance of the circuit.

47. D. Power Voltage (volts) P = VI Current (amps) Power (watts)

48. Calculate power • A light bulb with a resistance of 1.5Ω is connected to a 1.5-volt battery in the circuit shown at right. • Calculate the power used by the light bulb.

49. Paying for electricity • Electric companies charge for the number of kilowatt-hours used during a set period of time, often a month. • One kilowatt-hour (kWh) means that a kilowatt of power has been used for one hour. • Since power multiplied by time is energy, a kilowatt-hour is a unit of energy. • One kilowatt-hour is 3.6 x 106 joules.

50. Calculate power • Your electric company charges 14 cents per kilowatt-hour. Your coffee maker has a power rating of 1,050 watts. • How much does it cost to use the coffee maker one hour per day for a month?