Part A Review | Constants The filament of a lightbulb has a resistance of R0 = 12 at 20 °C and 140 when hot. 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). Use the equation pà = Po (1+ a(T – To)), assuming an average temperature coefficient of resistivity a = 0.0045 (C°)-1. Express your answer using two significant figures. T = V ΑΣΦ Submit Request Answer Part B °C In this temperature range, what is the percentage change in resistance due to thermal expansion? Express your answer using two significant figures. ΕΠΙ ΑΣΦ Rexpansion-Ro Ro Submit Request Answer Part C ? What is the percentage change in resistance due solely to the change in p? Express your answer using two significant figures. ΑΣΦ Rchange in p Ro Ro Submit Request Answer ?

Most electrical appliances are rated in watts. Does this rating depend on how long the appliance is on? (When off, it is a zero-watt device.) Explain in terms of the definition of power.

CASE STUDY A person in Franklins time may have been able to provide the same advice we came up with in Example 23.2. However, an 18th-century person may have had a different reason for his or her advice. What part of that persons explanation would be the same as ours? What would be different?

A cyclometer is a device mounted on a bicycle that records and displays trip information such as elapsed time, distance traveled, and average speed. Modern versions employ small magnets attached to a spoke on either the front or rear wheel and a sensor located on the front fork or rear frame. As the magnet is carried past the detector once each wheel revolution, it produces an electrical pulse that is recorded and logged by an integrated circuit in the device. The distance traveled equals the total number of revolutions multiplied by the circumference of the wheel. (a) A typical mountain bike has a wheel diameter of 26 in. How far will a cyclist have traveled in both miles and kilometers if her cyclometer indicates that her front wheel has made 25,000 revolutions during her trip? (b) If the cyclometer clock shows that the elapsed time for the trip was 2 hours and 40 minutes, what was the rider’s average speed during this period?