A convex lens has power P. It is cut into two halves along its principal axis. Further one piece (out of the two halves) is cut into two halves perpendicular to the principal axis (as shown in figure). Choose the incorrect option for the reported pieces. 

Concept :

When a convex lens is cut along the principal axis, the power of each half remains the same as the original lens. When further cut perpendicular to the principal axis, the power of each piece is halved.

Calculation:

Let's denote the pieces as L₁, L₂, and L₃ as shown in the figure.

⇒ The original lens has power P.

⇒ When cut along the principal axis, the power of each half remains the same:

⇒ Power of L₁ = Power of L₂ = P

⇒ When L₂ is further cut perpendicular to the principal axis:

⇒ Power of each piece (L₂ and L₃) becomes P/2.

⇒ Power of L₂ = P/2

⇒ Power of L₃ = P/2

The incorrect option is:

1) Power of L₁ = P/2

Therefore, the correct answer is option 1.