# 1. What is EM radiation?

1.      What is EM radiation? Explain some key differences between ionizing EM radiation and other forms of EM radiation, giving an example of each.

2.      What are a two different ways that ionizing radiation can hurt people?

3.      What is the linear hypothesis for radiation exposure? Is it used for anything practical? Is it proven?

4.      Suppose you learn that a hospital X ray imaging machine is subjecting patients to 50% more radiation that it is supposed to do. Why or why not would this be cause for concern?

5.      Suppose a patient needs a CAT scan to verify that there is no intracranial bleeding. What would you say about the dangers and on what basis?

6.      All light—whether visible of invisible is ____ radiation. (Fill in the blank.) Name three forms of invisible light, saying in what important way they differ. What are some sources and uses of the forms you mention?

7.      In what ways could non-ionizing radiation hurt people? (Please consider two different forms of non-ionizing radiation.)

8:

a.   The number of photons per second in a 5 mW green (nm) laser beam.

b.  The number of photons per second in a 5 mW red () laser beam.

c.   The number of photons per second in a 200 mW green () laser beam.

d.  Compare the energy (by ratio!) of one photon of visible light to one photon of an X ray. Select a particular (nominal) wavelength for each.

e.  The intensity of a 200mW green () laser beam at 5 m distance. Assume the laser has spread to a circle of 3 mm diameter. (Lasers are special in two ways: they produce light at a single wavelength and create a highly focused, narrow beam that barely widens as it transmits from the source.)

f.    The intensity of a light bulb, producing 10 W of light, at 5 m distance. To a good approximation, the light bulb shines equally in all directions, so you need to divide the power by the surface of a sphere of radius 5m.

g.   Even though the lightbulb produces 10 W of light and the laser only 200 mW (compare by ratio!), what do you notice about the intensity of the light blub vs. the laser at the 5 m distance?

*In the above, recall that photons are packets of energy. Each photon has energy E = hf where h is Planck’s constant, 6.6 × 10-34 m2 kg / s, E is the energy in Joules, and f is the frequency in Hz (same as 1/s). Usually, instead of the frequency, the wavelength is used to characterize EM sources. Recall that  where λ is the wavelength and c is the speed of light 3.0 × 108 m/s. 