# s71 - Solutions to Homework#7 Chapter 25 38 Picture the...

This preview shows pages 1–2. Sign up to view the full content.

Solutions to Homework #7 Chapter 25 38. Picture the Problem: To obtain optimal reception of a 66.0-MHz TV signal, the length of the antenna should be equal to half a wavelength. Strategy: Set the length of the antenna equal to half a wavelength, where the wavelength is given in terms of the frequency using equation 25-4. Solution: Calculate the length of the antenna: ( 29 8 7 1 3.00 10 m/s 2.27 m 2 2 2 6.60 10 Hz c L f λ = = = = Insight: To listen to an FM radio station at 107 MHz the antenna should be 1.40 m long. 44. Picture the Problem: The radiation pressure exerted by beam of light 1 is half the radiation pressure of beam of light 2. Strategy: Use the expressions 2 0 I c E ε = (equation 25-10) and av av pressure I c = (equation 25-12) to determine the rms electric field in beam 2. Solution: We note from equation 25–12 that the radiation pressure depends on the intensity of a wave. The intensity, in turn, depends on the square of the fields, as equation 25–10 shows. Therefore, the electric field in beam 2 has a magnitude of 0 2 . E 2. (b) The intensity of an electromagnetic wave, on the other hand, depends on the square of the electric and magnetic fields. As a result, doubling the fields quadruples the intensity of the wave. We conclude the rms average intensity of the wave changes by a multiplicative factor of 4.00. Insight: The answer can also be determined by a ratio: av, 2 0 av, 2 av, 2 av, 2 2 2 2 0 1 1 0 av, 1 av, 1 av, 2 2 av, 1 0 pressure pressure 2 2 pressure pressure I c I c E E E E E E I c I c ε ε = = = = = = = 62. Picture the Problem: A 75.0-W light bulb emits electromagnetic waves uniformly in all directions. Strategy: Use equation 14-7 to calculate the intensity of the light 2.5 m from the source. Insert the intensity into equation 25-10 to calculate the rms electric field, and then solve equation 25-9 for the magnetic field. Solution: 1. Divide the power by area: ( 29 2 av av 2 75.0 W 0.955 W/m 4 2.50 m P I A π = = = 2. Calculate the electric field: ( 29 ( 29 2 av 0 rms 2 av rms 8 12 2 2 0 0.955 W/m 19.0 V/m 3.00 10 m/s 8.85 10 C / Nm I c E I E c ε ε - = = = = 3. Find the magnetic field: 8 rms rms 8 19.0 V/m 6.33 10 T 63.3 nT 3.00 10

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern