Add pset 9 questions

_psets/9.md

+---
+title: Problem Set 9
+---
+
+## (9.6)
+
+{:.question}
+Solve the periodically forced Lorentz model for the dielectric constant as a function of frequency,
+and plot the real and imaginary parts.
+
+
+## (12.1)
+
+### (a)
+
+{:.question}
+How many watts of power are contained in the light from a 1000 lumen video projector?
+
+### (b)
+
+{:.question}
+What spatial resolution is needed for the printing of a page in a book to match the eye’s limit?
+
+
+## (12.2)
+
+### (a)
+
+{:.question}
+What is the peak wavelength for black-body radiation from a person? From the cosmic background
+radiation at 2.74 K?
+
+### (b)
+
+{:.question}
+Approximately how hot is a material if it is “red-hot”?
+
+### (c)
+
+{:.question}
+Estimate the total power thermally radiated by a person.
+
+
+## (12.3)
+
+### (a)
+
+{:.question}
+Find a thickness and an orientation for a birefringent material that rotates a linearly polarized
+wave by $$90^\circ$$. What is that thickness for calcite with visible light ($$\lambda \approx 600
+\si{nm}$$)?
+
+### (b)
+
+{:.question}
+Find a thickness and an orientation that converts linearly polarized light to circularly polarized
+light, and evaluate the thickness for calcite.
+
+### (c)
+
+{:.question}
+Consider two linear polarizers oriented along the same direction, and a birefringent material
+placed between them. What is the transmitted intensity as a function of the orientation of the
+birefringent material relative to the axis of the polarizers?