1. In a dentist's office an X-ray of a tooth is taken using X-rays that have a frequency of 6.28 10¹⁸ Hz. What is the wavelength in vacuum of these X-rays?

2. Review Conceptual Example 3 for information pertinent to this problem. When we look at a particular star, we are seeing it as it was 595 years ago. How far away from us (in meters) is the star? Take a year to be 365.25 days.

3. A plate glass window (n = 1.5) has a thickness of 3.4 mm. How long does it take light to pass perpendicularly through the plate?