Physics 202 MWF 10:20 Spring 1999 (Ford)

Chapts. 24, 25 and 26(sects 1--8) in Cutnell and Johnson 4e

Exam III

Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(15 pts) 1. The average intensity of a cylindrical laser beam is 0.800 W/m². The cross sectional area of the beam is 3.0 × 10^-4 m² and the average intensity is uniform across the cross section of the beam.

a) What is the average power output of the laser?

Ans. _________________

b) What is the rms value of the electric field in the beam?

Ans. ____________

c) How much energy is contained in a 0.500 m length of the beam?

Ans. _____________


(15 pts) 2. A distant galaxy emits light that has a wavelength of 427.0 nm. The galaxy is moving away from the earth at a speed of 5.0 × 10⁶ m/s. What is the wavelength of this light as measured on earth?

Ans. ______________

(16 pts) 3. Unpolarized light of intensity 200 W/m² passes through two polarizing filters. The angle between the transmission axis of the first filter and of the second filter is 37°. What is the intensity of the light after it has passed through the second filter?

Ans. _______________


(16 pts) 4. A ray of light with frequency f = 5.0 × 10¹⁴ Hz is traveling in glass and strikes a flat glass/liquid interface. The angle of incidence is 50° and the refractive index of the glass for light of this frequency is n = 1.70.

a) What is the wavelength of the light in the glass?

Ans. ______________

b) What is the largest index of refraction that the liquid can have (for light of this frequency), such that none of the light is transmitted into the liquid and all is reflected back into the glass?

Ans. _____________


(18 pts) 5. An object 2.0 mm tall is placed to the left of a concave spherical mirror that has f = +15 cm. The height of the image is 5.0 mm and the image is upright.

a) Is the image real or virtual?

Ans. ______________

b) How far is the object from the mirror?

Ans. _____________

(20 pts) 6. An object 2.0 mm tall is placed 30.0 cm to the left of a thin lens. The image formed by the lens is 20.0 cm to the left of the lens.

a) Is the image real or virtual?

Ans. _____________

b) Is the image upright or inverted?

Ans. _____________

c) What is the height of the image?

Ans. ______________

d) What is the focal length of the lens? Be sure to indicate whether the focal length is positive or negative.

Ans. _______________