1. The semiconducting compound CdSe is widely used for light emitting diodes (LEDs). The energy gap in CdSe is 1.8 eV. What is the frequency of the light emitted by a CdSe LED?

2. The resistivity of a sample of pure silicon diminishes drastically when it is irradiated with infrared light of wavelength less than 1.13 mm. What is the energy gap of silicon?

3. When a thin slab of semiconducting material is illuminated with monochromatic light most of the light is transmitted through the slab if the wavelength is greater than 1.85 μm. For wavelengths less than 1.85 μm, most of the incident light is absorbed. Determine the energy gap of this semiconductor.