(III) The filament of a lightbulb has a resistance of 12 Ω at 20°C and 140 Ω when hot (as in Problem 19). ( a ) Calculate the temperature of the filament when it is hot, and take into account the change in length and area of the filament due to thermal expansion (assume tungsten for which the thermal expansion coefficient is ≈ 5.5 × 10 −6 C° −1 ). ( b ) In this temperature range, what is the percentage change in resistance due to thermal expansion, and what is the percentage change in resistance due solely to the change in ρ ? Use Eq. 25–5.
(III) The filament of a lightbulb has a resistance of 12 Ω at 20°C and 140 Ω when hot (as in Problem 19). ( a ) Calculate the temperature of the filament when it is hot, and take into account the change in length and area of the filament due to thermal expansion (assume tungsten for which the thermal expansion coefficient is ≈ 5.5 × 10 −6 C° −1 ). ( b ) In this temperature range, what is the percentage change in resistance due to thermal expansion, and what is the percentage change in resistance due solely to the change in ρ ? Use Eq. 25–5.
(III) The filament of a lightbulb has a resistance of 12 Ω at 20°C and 140 Ω when hot (as in Problem 19). (a) Calculate the temperature of the filament when it is hot, and take into account the change in length and area of the filament due to thermal expansion (assume tungsten for which the thermal expansion coefficient is ≈ 5.5 × 10−6 C°−1). (b) In this temperature range, what is the percentage change in resistance due to thermal expansion, and what is the percentage change in resistance due solely to the change in ρ? Use Eq. 25–5.
(b) 1. A platinum resistance sensor has a resistance of 100 2 at 0 °C and a temperature
coefficient of resistance (oc) of 4 x 10 "C. If the resistance of the sensor is 125
O, find the corresponding temperature of the sensor.
ii. A variable dielectric capacitive displacement sensor consists of two square metal
plates of side 5 cm, separated by a gap of 1 mm. A sheet of dielectric material 1
mm thick and of the same area as the plates can be slide between them as shown
in Figure Q.4b. Given that the dielectric constant of air is 1 and that of the dielectric
material is 4, calculate the capacitance of the sensor when the input displacement
x-0.0 cm, 2.5 cm and 5,0 cm.
Figure Q4b
(b) Consider a particular phone that has a battery rated at 2.500 mAh. The battery operates at a potential difference of 3.90 V. How much energy, in units of kilowatt-hours, is stored in
a fully charged battery?
0.975-2
✓kWh
(c) If electricity costs $0.16 (or 16.0 cents) per kilowatt-hour, what is the value of the total amount of energy stored in this battery? Express your answer in cents (or 0.01 of a dollar).
How can you relate the energy from part (b) to the cost per kilowatt-hour to find the total cost?
(d) When the phone is idle (that is, turned on but not making calls or texts, using GPS, or running any power-hungry apps), it will operate continuously for 32.2 hours from a fully
charged battery, until the battery runs out. How much average current does the phone draw while idle? Express your answer in milliamperes,
MA
(b)
A voltage of 3 V is applied across the ends of a copper alloy conductor
which has a resistance of 1.5 at room temperature (20 °C). The
conductor has a length of 20 m and a diameter of 0.7 mm.
(i)
(ii)
(iii)
Calculate the current which flows through the copper alloy
conductor and the current density in it.
What is the electrical conductivity of the material?
After a while, the temperature in the copper alloy conductor rises
and its resistance becomes 2.4 №. If the temperature coefficient of
resistance of the copper alloy is 0.004/°C at 20 °C, calculate the
temperature to which the conductor has risen.
Chapter 25 Solutions
Physics for Scientists and Engineers with Modern Physics
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How To Solve Any Resistors In Series and Parallel Combination Circuit Problems in Physics; Author: The Organic Chemistry Tutor;https://www.youtube.com/watch?v=eFlJy0cPbsY;License: Standard YouTube License, CC-BY