PHY205-HF	Problem Set 5	Prof. Jason Harlow
“The Physics of Everyday Life”	Due December 1, 2005	Physics Department, University of Toronto

Please complete the following problems on separate paper. Make sure your name, T.A.’s name, and tutorial day (Mon or Wed) is written at the top of your problem set. Show all your reasoning and work legibly, and draw a box around the final numerical or single-word answer where applicable. You may turn your problem set either directly to Professor Harlow or your T.A., or you may drop it in your T.A.’s designated drop box at the base of the stairs outside the lecture hall, in the basement of MP. Any work received after 7:00 PM on the due date will be considered late, and a late penalty will be applied.

1.1 (1 point) Porous, unglazed ceramics can absorb water and moisture. Why are they unsuitable for use in a microwave oven?

1.2 (1 point) Why are microwavable dinners packaged in plastic or cardboard rather than aluminum trays?

1.3 (1 point) Why is it so important that a microwave oven turn off when you open the door?

2.1 (1 point) The yellow light from a sodium vapour lamp has a frequency of 5.08×10¹⁴ Hz. How much energy does each photon carry?

2.2 (1 point) A particular X-ray has a frequency of 1.2×10¹⁹ Hz. How much energy does its photon carry?

2.3 (1 point) Which photon could cause more damage to the nucleus of one of your cells?

3. (2 points) When you stand at the edge of a lake and try to look into the water, you mostly see a reflection of the sky. You’re considering designing sunglasses specially designed for fishermen. If you are interested in seeing fish down in the water, is it better to block horizontally polarized light, vertically polarized light, or both? Why?

4. (2 points) Light from a distant object approaches the objective lens of a telescope as a group of parallel light rays. Please draw a picture of the light rays from three stars passing through a converging lens to show that they focus at three separate locations.

5. (1 points) You’re trying to take a photograph of two small statues with a 200 mm telephoto lens. One statue is 4 m from the lens, and the other statue is 5 m from the lens. The real image of which statue forms closer to the lens?

6. (4 points) An ⁵⁷Fe atom sits in one of your blood cells, and moves about in your body. The name of this element is iron. You breathe in some Radon gas, which naturally occurs in the air. A Radon nucleus decays while it is in your lungs, and as a result, a neutron enters your body and is absorbed by the nucleus of the ⁵⁷Fe atom.

6.1 What is the new number, symbol and element name for the atom?
6.2 Does the change in the nucleus affect the number and arrangement of electrons in the atom that is built around this nucleus?

Next, you walk outside and a naturally occurring cosmic ray enters your body. As a result the same nucleus from the previous question absorbs a proton.

6.3 What is the new number, symbol and element name for the atom?
6.4 Does the change in the nucleus affect the number and arrangement of electrons in the atom that is built around this nucleus?

Some suggested problems (not to be turned in):

Practice 1. In air, green light has a frequency of about 5.5×10¹⁴ Hz and a wavelength of about 520 nanometres. If this light enters a bowl of water, will the frequency change? Will the wavelength change? In both cases, if the answer is yes, will the number increase or decrease?

Practice 2. When astronauts walked on the surface of the moon, they could see the stars even though the Sun was overhead. Why can’t we see the stars while the Sun is overhead?

Practice 3. Why is a pile of granulated sugar white while a single large piece of rock candy (solid sugar) is clear?

Practice 4. On a bright, sunny day you can use a magnifying glass to burn wood by focusing sunlight onto it. The focused sunlight forms a small circular spot of light that heats the wood. If you cover the left half the magnifying glass with an opaque sheet of paper, what will be the shape of the small spot?

Practice 5.1 As you zoom the lens of your video camera inward to take a close-up of a person, what characteristic of the lens changes and does it increase or decrease?

Practice 5.2 The real image formed by the lens of a video camera lands on a CCD (charge coupled detector), which detects the light. As you zoom this video camera, how does the distance between the effective centre of the lens and the CCD change?

Practice 6. Why is it important to keep foods and drugs out of direct sunlight, even when they’re not in danger of overheating?