The applet below allows you to investigate the reflective properties of an ellipse. Move the mouse on the screen below. When it is "inside" the parabola, a set of crosshairs will appear. When the mouse is clicked, a light ray passes through this point and the left focus is drawn. When the ray hits the ellipse it is reflected, and you can see the path of the reflected ray for 3 reflections. If you drag the mouse while it is clicked, you can move the location of your light ray. The ray can be erased by clicking the button. The width of the ellipse can be changed by moving the slider. Notice how the locations of the foci changes as well.