PHY 102 1st EditionOutline of Last Lecturei. Continued Examplesa. Example 1b. Example 2c. Example 3d. Example 4ii. Other Properties of Wavesa. Polarizationb. Diffractionc. Interferenced. Doppler Shift/Effectiii. Light Propertiesiv. Electricitya. Example Dischargesb. Electrical Charges c. Electrical Field Strengthd. Coulomb’s LawOutline of Current Lecture I. Why Gravity Dominates the UniverseThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Electrical charge/Gravitational ForceII. Compasses and Lodestonesa. Magnetic compassIII. Earth’s Magnetic Fielda. Reducing magnetic fieldIV. Fields in PhysicsV. Fields cont’dVI. Fields cont’dVII. Magnetism from ElectricityVIII. Faraday’s Lines of ForceCurrent LectureI. Why Gravity Dominates the Universea. Because Fe/Fg = 4.17 x 1042 and Fe >>>> Fg, then why does gravity dominate the universe?i. Electrical forces are SO much greater than gravitational forcesii. No electrical force dominating the earth because the earth is neutralP+e+p+Forces are opposite and equal and cancel out electrical effectb. The universe is “neutral” in terms of overall charge; that is, the number of electrons is balanced by the number of protonsc. Individual objects are most commonly neutral because they contain roughly equal numbers of positive and negative chargesII. Analogues (corresponding parts)a. Fe = keq1q2/r2 where ke = 9 x 109 Nm2/C2i. Analogously Fg = Gm1m2/r2ii. However, Fg is only attractive. (unless we are talking about the grand scale of the universe…) whereas Fe can be either attractive or repulsiveb. Fe = qE (Force due to electrical field)i. Analogously W = mg (force due to gravitational field)1. W is downward,2. m is a scalar3. g is directed downwardii. This is why g is sometimes called the gravitational field strength and is expressed in units of N/kgIII. Sample Problemsa. What is the electrical field strength 1 meter away from a 1C positive charge? (Hint: Use both formulas on last slide eliminating one “q”.)Want to find the electrical field (E = ?)1C = 1018 p+EObject (1C or 1018 p+)1mE = ?Fe = EqFe = kQq/r2Eq = kQq/r2E = kQ/r2 = (9x109 nm2/c2)(1C)/(1m)2b. What is the direction of the field 1 m away from the 1C charge, in or out of the 1C charge?Answer: awayc. What force would a 1.4 x 10-5 C negative charge experience at 1m distance from the 1C positive charge?F = kQq/r2F = (1.4 x 10-5)(1C)/(1m)2d. Other notesi. If an electric force is greater than 0, it is considered repulsiveii. If an electric force is less than 0, it is considered attractiveIV. Compasses and Lodestonesa. Magnetic compass known from ancient timesi. Chinese probably the first (Marco Polo reported)1. Chinese would take needles and stroke them on lodestones and set them in water which would point north to tell directionsii. Compass needle prepared from lodestoneiii. Needles float on wateriv. Compasses have “north” and “south” ends1. The north end of a compass is the end that points northv. Like poles repel – opposites attractvi. Magnetic monopoles do not exist1. If you cut a magnet in half, it becomes north-south, not just north or just south2. Electric monopoles do existV. Earth’s Magnetic Fielda. Earth acts as though there is a large bar magnet at its centeri. With its south magnetic pole around 4° from Earth’s north geographic poleb. On the Move and Weakeningi. The “north” end of the compass points to the south magnetic pole of the Earthii. The magnetic south pole is located north of Canada and is on the moveiii. Strength is currently decreasing at a rate of about 6.3% per centuryiv. Electrical currents do not like magnetic fields – interfere VI. Fields in Physics 1a. A field is a hypothetical construct design to explain action at a distanceb. Two types of forces:i. Contact forces1. Pushing and pullingii. Action-at-a-glance forces1. Gravitational force2. Electrical force3. Magnetic force4. Certain nuclear force (weak and strong)VII. Fields in Physics 2a. Gravitationali. Arrows indicate direction motion of any matter1. Test particle in magnetism is a gram of matter2. Always attractive on a small scaleb. Electricali. Arrows indicate direction of a motion of a positive test particle, p+ (a proton)ii. Opposites attract; likes repelc. Magnetic:i. Arrows indicate direction of a motion of a north “monopole” – WHICH DONOT EXISTVIII. Fields in Physics 3a. Concentration of field lines indicate field strengthi. Closer the lines are, the more intense the fieldii. The more intense the field, the stronger the attractive or repulsive force.iii. When lines point in the same direction, this indicates attraction and vice versaIX. Magnetism from Electricitya. Oersted shows that direct (one way) flowing electricity produces a constant magnetic fieldi. Teaching a lecture and uses a wire to show electricityii. Has a compass near the electrical current-carrying wireiii. When the current begins in the wire, the compass needle moves1. When you run electricity through a wire, it produces a magnetic fieldb. Ampere shows that parallel current carrying wires have an attractive force between them.c. Ampere argues that currents flowing within the earth are responsible for the planet’s magnetic fieldi. Dynamo – theory to explain electrical magnetic fieldsd. Moon has a small/nonexistant magnetic field because it has little volume compared to the surface area so it does not have an electrical current strong enoughX. Faraday’s Lines of Forcea. Field lines trace out magnetic fieldsb. Magnetic fields are directed from N to Sc. A long, current carrying wire produces a circular consistent with the right hand rulei. Thumb points in directions of current flowii. Fingers point in directions of magnetic fieldiii. Current carrying wire is held in the fingers straight up and downd. Magnetic fields of currents – the solenoidi. If your magnetic field is stationary, there is no electric currentii. If the magnetic moves in relation to a wire, the electric current moves in relation to the magnete. Charged particles (+ and -) moving in a magnetic field experiences a force, F, but only so long as v is not parallel to B.f. The direction of the force is given by right hand rule 2i. Current is defined to flow in the same direction as a positive test