1. PHY 102 Problems Chapter 24

2. Problem 24.1 - 1 During a flare-up from a sunspot, X-rays (electromagnetic radiation) are emitted The distance between the sun and the earth is 1.50 x 10 11 m How long (in minutes) does it take for the X-rays to reach the earth?

3. Problem 24.1 - 2 Speed of electromagnetic radiation in vacuum is 3 x 10 8 m/s d = vt t = d / v = 1.50 x 10 11 m / 3 x 10 8 m/s t = 500 s = 8.3 minutes

4. Problem 24.2 A laser emits a narrow beam of light The radius of the beam is 1.0 x 10 -3 m The power is 1.2 x 10 -3 W What is the intensity of the laser beam? Area =  r 2 =  (1 x 10-3) 2 = 3.14 x 10 -6 I = power/area = 1.2 x 10 -3 / 3.14 x 10 -6 I = 382 W/m 2

5. Problem 24.3 The microwave radiation left over from the Big Bang explosion of the universe has an average energy density of 4 x 10 -14 J/m 3 What is the rms value of the electric field of this radiation? avg u =  0 E 2 rms 4 x 10 -14 = 8.85 x 10 -12 E 2 rms E 2 rms = 0.0045 E rms = 0.07 N/C

6. Problem 24.4 - 1 Linearly polarized light is incident on a piece of polarizing material What is the ratio of the transmitted light intensity to the incident light intensity when the angle between the transmission axis and the incident electric field is (a) 25 0 (b) 65 0

7. Problem 24.4 - 2 avg S/avg S 0 = cos 2  (a) avg S/avg S 0 = cos 2 25 = 0.82 (b) avg S/avg S 0 = cos 2 65 = 0.18