1. Joe and his lab partner Curly exposed the film in their pinhole camera on a bright, sunny day for 3 minutes instead of 30 seconds as instructed. Assuming that they did everything else correctly, answer the following questions about their negative.
a. Would you expect their negative to have more or fewer silver atoms on it? Briefly
explain your answer. 3 pts
They will have more silver atoms on it, since the normal exposing time is 60 seconds and they should decline the exposing time during a sunny day.
2.Transition or photo-gray glasses darken when exposed to ultra violet light. UV light catalyzes a redox reaction similar to the one used with photographic film. Initially, photo-gray glasses had crystals of silver chloride (AgCl) and copper chloride (CuCl) embedded in the molten glass before it hardened. When ultraviolet light struck the glasses, a redox reaction occurred and the silver ions were reduced to silver atoms making the lens darker – like sunglasses. The concentration of silver atoms was designed to darken the lens just enough to block ~80% of the transmitted light.
In the absence of UV light (when you’re indoors), the copper ions (Cu+) catalyzed another redox reaction which converted the silver atoms back into the original Ag+ and Cl- ions. As the silver atoms became silver ions, the glasses became transparent and clear again. Most of today’s transition lens are now plastic instead of glass. Plastic lens use organic molecules to make transition lens – not AgCl and CuCl.
a. In glass transition lens, which ion is oxidized and which is reduced? 2 pts
b. The windows of some cars block the transmission of UV light into the car. How would this affect the ability of photo gray glasses to function inside of a car? Briefly explain. 3 pts
3. The electromagnetic spectrum shown below has a range of wavelengths from high energy gamma rays (10-14 meters long) to low energy radio and TV waves (102 – 104 meters long). Ultraviolet light is the main catalyst for the redox reaction involved in black and white photographic paper because it has enough energy to start the redox reaction. Find UV light on the spectrum. From the following observations, predict whether the X-ray scanners currently used at airports are likely to damage undeveloped print film. 3 pts
- Safe lights used in the dark room are red-colored light.
- Indoor light exposures must be much longer due to the relative absence of ultraviolet light.