2- chapter27-question21 A wire of Nichrome (a nickel-chromium-iron alloy commonly used in heating elements) is 1.0m long and 1.0 mm in cross-sectional area, It carries a current of 4,0 A when a 2.0 V potential difference is applied between its ends. Calculate the conductivity of Nichrome. Option1 Option2 Option3 Option4 Option5 1.0 x 10 2.0 × 10 3.0 x 10 4.0 x 10 5.0 x 10% a) Option1 b) O Option4 =)O Option5 )O Option2 20114 Option3

2- chapter27-question21 A wire of Nichrome (a nickel-chromium-iron alloy commonly used in heating elements) is 1.0m long and 1.0 mm in cross-sectional area, It carries a current of 4,0 A when a 2.0 V potential difference is applied between its ends. Calculate the conductivity of Nichrome. Option1 Option2 Option3 Option4 Option5 1.0 x 10 2.0 × 10 3.0 x 10 4.0 x 10 5.0 x 10% a) Option1 b) O Option4 =)O Option5 )O Option2 20114 Option3

Physics for Scientists and Engineers, Technology Update (No access codes included)

9th Edition

ISBN:9781305116399

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter27: Current And Resistance

Section: Chapter Questions

Problem 27.4OQ

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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.
Residential building codes typically require the use of 12-gauge copper wire (diameter 0.205 cm) for wiring receptacles. Such circuits carry currents as large as 20.0 A. If a wire of smaller diameter (with a higher gauge number) carried that much current, the wire could rise to a high temperature and cause a fire. (a) Calculate the rate at which internal energy is produced in 1.00 m of 12-gauge copper wire carrying 20.0 A. (b) Repeat the calculation for a 12-gauge aluminum wire. (c) Explain whether a 12-gauge aluminum wire would be as safe as a copper wire.
Review. When a straight wire is warmed, its resistance is given by R = R0,[1 + a(T T0)] according to Equation 27.20, where a is the temperature coefficient of resistivity. This expression needs to be modified if we include the change in dimensions of the wire due to thermal expansion. For a copper wire of radius 0.100 0 mm and length 2.000 m, find its resistance at 100.0C, including the effects of both thermal expansion and temperature variation of resistivity. Assume the coefficients are known to four significant figures.
Integrated Concepts A 12.0-V emf automobile battery has a terminal voltage of 16.0 V when being charged by a current of 10.0 A. (a) What is the battery’s internal resistance? (b) What power is dissipated inside the battery? (c) At what rate (in °C/min ) will its temperature increase if its mass is 20.0 kg and it has a specific heat of 0.300 kcal/kg. °C, assuming no heat escapes?
A close analogy exists between the flow of energy by heat because of a temperature difference (see Section 19.6) and the flow of electric charge because of a potential difference. In a metal, energy dQ and electrical charge dq are both transported by free electrons. Consequently, a good electrical conductor is usually a good thermal conductor as well. Consider a thin conducting slab of thickness dx, area A, and electrical conductivity , with a potential difference dV between opposite faces. (a) Show that the current I = dq/dt is given by the equation on the left: ChargeconductionThermalconductiondqdt=A|dVdx|dQdt=kA|dTdx| In the analogous thermal conduction equation on the right (Eq. 19.17), the rate dQ/dt of energy flow by heat (in SI units of joules per second) is due to a temperature gradient dT/dx in a material of thermal conductivity k. (b) State analogous rules relating the direction of the electric current to the change in potential and relating the direction of energy flow to the change in temperature.
(a) Digital medical thermometers determine temperature by measuring the resistance of a semiconductor device called a thermistor (which has a= - 0.0600/°C ) when it is at the same temperature as the patient. What is a patient's temperature if the thermistor’s resistance at that temperature is 82.0% of its value at 37.0°C (normal body temperature)? (b) The negative value for a may not be maintained for very low temperatures. Discuss why and whether this is the case here. (Hint: Resistance can’t become negative.)
Review. Ail aluminum rod has a resistance of 1.23 at 20.0C. Calculate the resistance of the rod at 120C by accounting for the changes in both the resistivity and the dimensions of the rod. The coefficient of linear expansion for aluminum is 2.40 10-6 (C)-1
Unreasonable Results (a) What current is needed to transmit 1.00 102 MW of power at 10.0kV? (b) Find the resistance of 1.00 km of wire that would cause a 0.0100% power loss. (c) What is the diameter of a 1.00-km-long copper wire having this resistance? (d) What is unreasonable about these results? (e) Which assumptions are unreasonable, or which premises are inconsistent?
An all-electric car (not a hybrid) is designed to run from a bank of 12.0-V batteries with total energy storage of age of 2.00 107J. If the electric motor draws 8.00 kW as the car moves at a steady speed of 20.0 m/s. (a) what is the current delivered to the motor? (b) How far can the car travel before it is out of juice"?
Check Your Understanding Copper wires use routinely used for extension cords and house wiring for several reasons. Copper has the highest electrical conductivity rating, and therefore the lowest resistivity rating, of all nonprecious metals. Also important is the tensile strength, where the tensile strength is a measure of the force required to pull an object to the point where it breaks. The tensile strength of a material is the maximumamount of tensile stress it can take before breaking. Copper has a high tensile strength, 2108Nm2 A thirdimportant characteristic is ductility. Ductility is a measure of a material’s ability to be drawn into wires and a measure of the flexibility of the material, and copper has a high ductility. Summarizing, for a conductor to be a suitable candidate for making wire, there are at least three important characteristics: low resistivity, high tensile strength, and high ductility. What other materials are used for wiring and what are the advantages and disadvantages?
Resistors are commonly rated at 18W,14W,12W ,1 W and 2 W for use in electrical circuits. If a current of1 = 2.00 A is accidentally passed through a R=1.00 resistor rated at 1 W, what would be the most probable outcome? Is there anything that can be done to prevent such an accident?