The focal length of a small concave mirror is 2.5 cm. In order to use this concave mirror as a dentist's mirror, the distance of tooth from the mirror should be :

Options

A. 2.5 cm
B. 1.5 cm
C. 4.5 cm
D. 3.5 cm

Answer

To solve the problem of determining the distance of the tooth from the concave mirror for it to be used effectively as a dentist's mirror, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Purpose of the Concave Mirror**:
- A dentist uses a concave mirror to magnify the image of the tooth. For the image to be magnified, the object (tooth) must be placed within the focal length of the mirror.

2. **Identify the Focal Length**:
- The focal length of the concave mirror is given as 2.5 cm.

3. **Determine the Position of the Tooth**:
- For a concave mirror, when the object is placed within the focal length, the image formed is virtual, upright, and magnified. Therefore, the distance of the tooth from the mirror should be less than the focal length.

4. **Set Up the Condition**:
- Since the focal length is 2.5 cm, we need the distance of the tooth (denoted as 'd') to be less than 2.5 cm:
\[ d < 2.5 \text{ cm} \]

5. **Evaluate the Options**:
- The options provided are:
- A) 2.5 cm
- B) 1.5 cm
- C) 4.5 cm
- D) 3.5 cm
- From the condition \(d < 2.5 \text{ cm}\), we can see that the only option that satisfies this condition is 1.5 cm.

6. **Conclusion**:
- Therefore, the distance of the tooth from the concave mirror should be **1.5 cm**.

### Final Answer:
The distance of the tooth from the mirror should be **1.5 cm**.

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