Question

1.) A double-concave lens focal length -20 cm has an object placed at a distance of 30 cm in front of it. How far from the mirror is the image formed? On what side of the lens is the image formed? What is the magnification? Is the image real or virtual? Upright or inverted?

2.) The second order fringe is located 5-cm from the central fringe when formed by a 10 lines/mm diffraction grating on a screen 5 meters away. What is the wavelength of light being used?

3.) A three-layer parallel-boundary system consisting of air, then water (index of refraction 1.33), then glass (index of refraction 1.5) has light passing through it. The beam of light begins in the glass, refracting through the glass/water boundary, then undergoes total internal reflection at the water/air boundary. What must the angle of incidence be at the glass/water boundary?