The power of a lens whose focal length is one metre is ____ dioptre.

Options

A. one
B. ten
C. hundred
D. none of these

Answer

To find the power of a lens whose focal length is one meter, we can follow these steps:

### Step 1: Understand the formula for power of a lens
The power (P) of a lens is given by the formula:
\[ P = \frac{1}{f} \]
where \( P \) is the power in diopters and \( f \) is the focal length in meters.

### Step 2: Substitute the given focal length
In this case, the focal length \( f \) is given as 1 meter. We can substitute this value into the formula:
\[ P = \frac{1}{1} \]

### Step 3: Calculate the power
Now, we perform the calculation:
\[ P = 1 \]

### Step 4: State the final answer
The power of the lens is:
\[ P = 1 \text{ diopter} \]

Thus, the answer is **1 diopter**.

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