Laboratory experiment. In a laboratory experiment (shown in the gure below), the back focal distance of a lens system is determined to be +30 mm. The front focal distance is 120 mm. An object is placed 150 mm to the left of the lens and its image is observed 300 mm to the right of the lens. The system is in air, and the lens has a refractive index of 1.5. (a) Find the effective focal length. (b) Find the location of both the principal planes. (c) Find the magnication of the image. Figure 1: Setup for a laboratory experiment