When two thin lenses are placed in contact, the net power of the combination is equal to:

The correct option is The algebraic sum of individual powers.

Explanation

The power of a lens is defined as the reciprocal of its focal length (measured in meters), expressed as \( P = \frac{1}{f} \). It quantifies the degree to which a lens converges or diverges light. When two or more thin lenses are placed in contact, they function as a single equivalent lens system.

Detailed Analysis:

• According to the principles of ray optics, when two thin lenses with focal lengths \( f_1 \) and \( f_2 \) are placed in contact, the effective focal length \( F \) of the combination is determined by the formula:
  \( \frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2} \)
• Since Power \( P \) is the reciprocal of the focal length (\( P = \frac{1}{f} \)), the equation can be rewritten in terms of power:
  \( P_{net} = P_1 + P_2 \)
• This demonstrates that the net power of the combination is the algebraic sum of the individual powers.
• The term "algebraic sum" implies that the sign of the power (positive for converging/convex lenses and negative for diverging/concave lenses) must be considered during addition.

Key Takeaway:

For thin lenses in contact, the net power is the algebraic sum of individual powers (\( P_{net} = \sum P_i \)), while the effective focal length is found by adding the reciprocals of the individual focal lengths.