Question Detail
Question
A cell phone antenna is 8.5 cm long and is often designed to be ¼ wavelength long. Estimate the operating frequency of this phone, assuming the speed of light is 3.00 x 108 m/s.
Correct Answer
Option A is the correct answer.
Detailed Explanation
From page 6 (Example 31-4), the antenna length (L) is 8.5 cm = 0.085 m. If the antenna is ¼ wavelength, then λ = 4L = 4 * 0.085 m = 0.34 m. Using c = λf, we can find the frequency f = c / λ = (3.00 x 108 m/s) / 0.34 m ≈ 8.82 x 108 Hz, which is 882 MHz.
Hint
First, calculate the full wavelength from the antenna length, then use the speed of light formula.