Shashank went to the optician to get his eyes checked. He observed that the doctor combined two lenses and put these in front of his eyes so that he could see clearly. The powers of the two lenses used in the combination were -3 D and 4 D.
What type of lens will the combination of lenses be?

Options

A. diverging lens
B. converging lens
C. both converging and diverging since both types of lenses are used
D. either converging or diverging depending on the defect in Shashank's eyes

Answer

To determine the type of lens combination used by Shashank, we need to calculate the total power of the two lenses combined. The powers of the lenses are given as follows:

1. Power of the first lens (P1) = -3 D (diopters)
2. Power of the second lens (P2) = +4 D (diopters)

### Step 1: Calculate the total power of the lens combination
The total power (P) of two lenses in combination is given by the formula:
\[ P = P1 + P2 \]

Substituting the values:
\[ P = (-3 D) + (+4 D) \]
\[ P = -3 + 4 \]
\[ P = +1 D \]

### Step 2: Determine the type of lens based on the total power
The sign of the total power indicates the type of lens:
- If the power is positive, the lens is a **convex lens** (converging lens).
- If the power is negative, the lens is a **concave lens** (diverging lens).

Since we calculated the total power to be +1 D, this indicates that the combination of the lenses is a **convex lens**.

### Conclusion
The combination of the lenses used by Shashank is a **convex lens**.

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