practice

1. Write something.
2. Write something.
3. Write something.
4. Write something completely different.

conceptual

1. Two simple facts
   1. What is the source of all magnetism?
   2. What is the source of all electromagnetic waves?

numerical

1. An analogy.
   1. What is the separation between the scratches on a diffraction grating that would be used in a typical high school or undergraduate physics lab?
   2. What is the wavelength of the approximate center of the visible spectrum?
   3. What is the separation between the pickets of a picket fence?
   4. For what wavelength could a picket fence be used like a diffraction grating?
   5. What is the frequency of the electromagnetic wave with the wavelength calculated in part d?
   6. What kind of electromagnetic radiation is this?
2. A typical household microwave oven operates at a frequency of 2.45 GHz.
   1. What is the wavelength of this radiation?
   2. Hotspots in a microwave oven are caused by the formation of standing waves within the cooking chamber. What is the separation between hotspots in a 2.45 GHz microwave oven?
   3. How is the problem of hotspots dealt with in the design of microwave ovens or in the cooking techniques employed by the people that use them?
3. The lowest frequency of electromagnetic radiation used for communication purposes is at 76 Hz. This lies in the extremely low frequency (ELF) part of the radio spectrum.
   1. Who uses this frequency and for what purpose?
   2. What is the wavelength of this radiation?
   3. How long would a dipole antenna have to be to broadcast at this frequency?
   4. How does the antenna length you calculated in part a. compare to the circumference of the earth?
   5. How long is the actual antenna used for ELF communication?