A convex lens of power 4D is kept in contact with a concave lens of power 3D, the effective power of combination will be

Options

A. 1D
B. `3/4D`
C. 7D
D. `4/3D`

Answer

To find the effective power of a combination of a convex lens and a concave lens, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Powers of the Lenses**:
- The power of the convex lens (P1) is given as +4D (diopters).
- The power of the concave lens (P2) is given as -3D (diopters) because the power of concave lenses is taken as negative.

2. **Use the Formula for Effective Power**:
- The effective power (P_effective) of two lenses in contact is calculated using the formula:
\[ P_{effective} = P_1 + P_2 \]

3. **Substitute the Values**:
- Substitute the values of P1 and P2 into the formula:
\[ P_{effective} = 4D + (-3D) \]

4. **Perform the Calculation**:
- Simplifying the equation:
\[ P_{effective} = 4D - 3D = 1D \]

5. **Conclusion**:
- The effective power of the combination of the convex lens and the concave lens is **1D**.

### Final Answer:
The effective power of the combination is **1D**.

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