GENERAL PHYSICS 2

Please answer all of the Activities (1, 2 and 3) given below. Please provide the right answers with effective solutions. Please refer to the references given below also (right after the Activities image).

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ACTIVITIES

POINTS TO REMEMBER Conventional Current It assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. Electron Flow it is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source. There are four factors that affect the resistance of a wire; Resistance is inversely proportional to cross-sectional-area. The bigger the cross sectional area of the wire the greater the number of electrons that experience the 'electric slope' from the potential difference. As the length of the wire does not change each cm still gets the same number of volts across it - the potential gradient does not change and so the average drift velocity of individual electrons does not change. Although they do not move any faster there are more of them moving so the total charge movement in a given time is greater and current flow increases. This means resistance decreases. This does not give rise to astraight line graph as cross sectional area is inversely proportional to resistance not directly proportional to it. . Resistance (R) and Area (A) RIA1 = R2Az Resistance is proportional to length. If you take a wire of different lengths and give each a particular potential difference across its ends. The longer the wire the less volts each centimeter of it will get. This means that the 'electric slope' that makes the electrons move gets less steep as the wire gets longer, and the average drift velocity of electrons decreases. The correct term for this 'electric slope' is the potential gradient. A smaller potential gradient (less volts per meter) means current decreases with increased length and resistance increases. R1 R2 L LZ Example A wire is 100.0 cm long has a resistance of 25.0 0. It is cut into five equal parts a. What is the resistance of each piece of wire? b. If the five parts were bundled together, what is the resistance of the resulting wire: Solution a. Since the wire is divided into b. Since the parts were bundled five equal parts, then each together, the area increases piece will be 20.0 cm long. to FIVE times its original Let L2=20 cm and Rz be the value. Let Az be the area of resistance of each piece. each piece of wire and A3 be Since R is directly the new area; that is A3=5A2. proportional to L, then: Let R3 be the resistance of the bundled pieces of wire. Since R1 R2 R is inversely proportional to A, 250 R 2 R2AZ = R3As 100.0 cm 20.0 cm 50 A2 = R3 (5 A2) R2 = 50 R3 = 10Resistance depends on the material the wire is made of. . The more tightly an atom holds on to its outermost electrons the harder it will be to make a current flow. The electronic configuration of an atom determines how willing the atom will be to allow an electron to leave and wander through the lattice. Material p (Q.m) at Material p (R.m) at 20.C 20 0 Silver 1.59x 10-6 Lithium 9.28x 10-3 Copper 1.68x10-3 Iron 1.0x 10-7 Gold 2.44x 10-8 Platinum 1.06x10-7 Aluminum 2.82x 10-8 Tin 1,09x 10-7 Tungsten 5.60x 10-5 Lead 2.2x10-7 Zinc 5.90x 10-8 Mercury 9.8x10-7 Nickel 6.99x 10-8 The effect of the length, cross-sectional area, and material on resistance may be written as where Ris the resistance, resistivity, R-PA L length *cross-sectional area. Example An insulated extension cord is made of a 1.5m.long copper rod with a diameter of 2.3 mm. What is the resistance of the extension cord? Solution Solve for the cross-sectional area of the copper Given rod Lcopper 1.5 m Ted2 Acopper = my = = 4.15 X 10-6m2 4 dcopper: 2.3 mm= 2.3x10-3m 1.5 m Pcopper: 1.68x 10-8 R = p- = (1.68 x 10-60. m) 4.15 x 10-6m? R = 6.07 x 10-30Resistance increases with the temperature of the wire. The hotter wire has a larger resistance because of increased vibration of the atomic lattice. When a material gets hotter the atoms in the lattice vibrate more. This makes it difficult for the electrons to move without interaction with an atom and increases resistance. Where:" PT 'esistivity at temperature T' Po Resistivity at reference PT = Po+ pra(T -T.) temperature To RT RT = Ro + pra(T - T.) Resistance at T, Ro Resistance at To Temperature coefficient of resistance Temperature coefficients of Resistance of Some Materials at 20 C Material Material a Iron (Fe) 0.00651 Tin (Sn) 0.0042 Aluminum (Al) 0.00429 Tungsten (W) 0.0045 Gold (Au) 0.0034 Silicon (Si) - 0.07 Silver (Ag) 0.0038 Brass 0.0015 Platinum (Pt) 0.0039 Nickel (Ni) 0.00641 Copper (Cu) 0.00386 Mercury (Hg) 0.0009 Note: I have noticed that SOME values of Temperature coefficient of resistance differs from one website to another. Please use this table provided in solving the Activity problem. Example: Solution: The resistance of a platinum Since a is given at 20 C, the reference wire at 30 C is 15.0 0. Find temperature T, is 20 C. Solving for its resistance at 45.0 .C. resistance R20 at 20'C Note that R30 = R20 + Rzoa(30.0.C - 20'C) a =0.0039/ C at 20.0 .C 15.00 = R20 + R20 (0.0039/'C)(10 C) R20 = 14.40Given: Solving for Ras with T = 45.0'0 T = 30.0 C Ras = Rzo + Rzoo (45.0'0 - 20"C) R30 = 15.00 a = 0.0039/'C at 20 C RAs = 14.4 0 + 14.4 0(0.0039/"C) (25 0) R45 = 15.8 0 For more information of the lesson, please check these sites Conventional Current and Electric flow https://www.mi. mun.ca/users/cchaulk/eltk1100/ivse/ivse.htm# Factors that affect the resistance of a wire https://www.cyberphysics.co.uk/topics/electricity/higher_electricity/resistance.htmActivity 1 Problem Solving (Answer without solution will not be considered) The resistance of a rod with a length of 3.0m and a diameter of 1.0 cm is 56.02. If this rod is stretched to from a wire with a diameter of 0.01 cm, what is its resistance? Assume that in the process of stretch in the rod, its volume did not change. Activity 2 Problem Solving (Answer without solution will not be considered) An insulated extension cord is made of a 1.5m long aluminum rod with a diameter of 0.5 cm. What is the resistance of the extension cord? (Hint: solve for the cross-sectional area of the copper rod first) Activity 3 Problem Solving (Answer without solution will not be considered) A copper wire has a resistance of 15.0 Q at a temperature of 14 C. After a current passes through the windings, the resistance rose to 22.5 0. To what temperature whas the wird heated