a) Determine the effective focal length of the combination of the two lenses in Exercise, if they are placed 8.0cm apart with their principal axes coincident. Does the answer depend on which side of the combination a beam of paralel light is incident? Is the notions of effective focal length of this system useful at all?
b) An object 1.5 cm in size is placed on the side of the convex lens in the arrangement a) above. The distance between the object and the convex lens is 40cm. Determine the magnification produced by the two-lens system, and the size of the image.

Explanation

To solve the given problem, we will break it down into two parts as specified in the question.

### Part (a): Determine the Effective Focal Length

1. **Identify the Focal Lengths**:
- The focal length of the convex lens (f1) = +30 cm (positive because it's a converging lens).
- The focal length of the concave lens (f2) = -20 cm (negative because it's a diverging lens).
- The distance between the two lenses (d) = 8 cm.
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