67. You're estimating costs for a new power line with your compa- ny's financial group. Engineering specifies a resistance of 50 m2 per kilometer for the line. The costs and densities of copper and aluminum are, respectively, $6.86/kg and 8.9 g/cm³, and $2.23/kg and 2.7 g/cm³. Determine the cost per meter of each type of wire. Which is more economical?

67. You're estimating costs for a new power line with your compa- ny's financial group. Engineering specifies a resistance of 50 m2 per kilometer for the line. The costs and densities of copper and aluminum are, respectively, $6.86/kg and 8.9 g/cm³, and $2.23/kg and 2.7 g/cm³. Determine the cost per meter of each type of wire. Which is more economical?

College Physics

10th Edition

ISBN:9781285737027

Author:Raymond A. Serway, Chris Vuille

Publisher:Raymond A. Serway, Chris Vuille

Chapter17: Current And Resistance

Section: Chapter Questions

Problem 38P: A portable coffee heater supplies a potential difference of 12.0 V across a Nichrome heating clement...

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Integrated Concepts (a) Assuming 95.0% efficiency for the conversion of electrical power by the motor, what current must the 12.0-V batteries of a 750-kg electric car be able to supply: (a) To accelerate from rest to 25.0 m/s in 1.00 min? (b) To climb a 2.00 102-m- high hill in 2.00 min at a constant 25.0-m/s speed while exerting 5.00 102 N of force to overcome air resistance and friction? (c) To travel at a constant 25.0-m/s speed, exerting a 5.00 102 N force to overcome air resistance and friction? See Figure 20.44.
Integrated Concepts (a) What energy is dissipated by a lightning bolt having a 20,000-A current, a voltage of 1.00102 MV, and a length of 1.00 ms? (b) What mass of tree sap could be raised from 18.0°C to its boiling point and then evaporated by this energy, assuming sap has the same thermal characteristics as water?
The human body can exhibit a wide range of resistances to current depending on the path of the current, contact area, and sweatiness of the skin. Suppose the resistance across the chest from the left hand to the right hand is 1.0 106 . (a) How much voltage is required to cause possible heart fibrillation in a man, which corresponds to 500 mA of direct current? (b) Why should rubber-soled shoes and rubber gloves be worn when working around electricity?
Integrated Concepts (a) An immersion heater utilizing 120 V can raise the temperature of a 1.00 102 -g aluminum cup containing 350 g of water from 20.0°C to 95.0°C in 2.00 min. Find its resistance, assuming it is constant during the process. (b) A lower resistance would shorten the heating time. Discuss the practical limits to speeding the heating by lowering the resistance.
When a straight wire is heated, its resistance changes according to the equation R = R0 [1 + (T T0)] (Eq. 17.7), where is the temperature coefficient of resistivity. (a) Show that a more precise result, which includes the length and area of a wire change when it is heated, is R=R0[1+(TT0)][1+(TT0)][1+2(TT0)] where is the coefficient of linear expansion. (See Topic 10.) (b) Compare the two results for a 2.00-m-long copper wire of radius 0.100 mm, starting at 20.0C and heated to 100.0C.
Knowing that the severity of a shock depends on the magnitude of the current through your body, would you prefer to be in series or parallel with a resistance, such as the heating element of a toaster, if shocked by it? Explain.
Combine Ohm’s law and the equation for power consumption to derive the equation that gives the power in terms of current and resistance. Use the result to answer the following question. A cable carrying electrical energy wastes 10 kWh of energy each day because of ohmic heating. If the current in the cable is doubled but the cable’s resistance remains the same, how much energy will it waste each day?
-gauge copper wire has a diameter of 9.266 mm. Calculate the power loss in a kilometer of such wire when it carries 1.00102 A.
When an unknown resistance Rxis placed in a Wheatstone bridge, it is possible to balance the bridge by adjusting to be 2500 . What is Rxif R2R1 = 0.625?
What is the resistance of a 20.0-m-long piece of 12-gauge copper wire having a 2.053-mm diameter?
Find the resistance that must be placed in paralled with a 25.0- galvanometer having a 50.0A sensitivity (the same as the one discussed in the text) to allow it to be used as an ammeter with a 300-mA full-scale reading.
A nichrome rod that is 3.00 mm long with a cross sectional area of 1.00 mm2 is used for a digital thermometer, (a)What is the resistance at room temperature? (b)What is the resistance at body temperature?