Physics 202 MWF 10:20 Spring 1993 (Ford)
Exam IV Chapts. 37,38,39,41 in SZY College Physics 7th ed.


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


(17 pts) 1. When ultraviolet light with a wavelength of 160 nm falls on a certain metal surface the maximum kinetic energy of the emitted photoelectrons is 1.8 eV. What is the longest wavelength of light that will produce photoelectrons from this surface?

Ans. _______________


(16 pts) 2. Recall that the energy levels of the hydrogen atom are given by E_n = -Rch/n², where R = 1.097 × 10⁷ m^-1} and Rch = 13.6 eV. What is the frequency f of the photon emitted when a hydrogen atom undergoes a transition from the n = 3 to the n = 1 level?

Ans. _____________


(14 pts) 3. Coherent light with wavelength 400 nm from a distant source is incident on a slit 0.80 mm wide and the resulting diffraction pattern is observed on a screen 2.00 m from the slit. What is the distance on the screen between the first two minima that lie above the central maximum?

Ans. _______________


(17 pts) 4. A plastic film with index of refraction 2.5 is put on the surface of a car window to increase the reflectivity and keep the interior of the car cooler. The window glass has index of refraction 1.6. What minimum thickness of the plastic film is required if light of wavelength (measured in air) 600 nm reflected from the two sides of the film is to interfere constructively?

Ans. _________________


(18 pts) 5. A concave mirror with a focal length of magnitude |f| =2.0 cm forms an image of a 40.0 cm tall object that is to the left of the mirror. The image is 5.0 cm tall and is inverted.

a) What is the distance of the object from the mirror vertex?

Ans. ______________

b) What is the distance of the image from the mirror vertex? Is the image real or virtual?

Ans. ____________

_____________


(18 pts) 6. Two lenses are placed 20 cm apart as shown in the sketch. The first lens has focal length 4.0 cm and the second lens has focal length 2.0 cm. When an object is placed to the left of the first lens the final image formed by the second lens is at infinity. What is the distance of the object from the first lens?

Ans. _______________