Question

The lens formula is given by :
\[\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\]
Which of the following correctly identifies each term in the formula?

• A. f = focal length, v = object distance, u = image distance
• B. f = focal length, v = image distance, u = object distance
• C. f = image distance, v = object distance, u = focal length
• D. f = object distance, v = focal length, u = image distance

Hint:

To avoid confusion between the lens and mirror formulas:
- Mirror formula: \(\frac{1}{f} = \frac{1}{v} + \frac{1}{u}\)
- Lens formula: \(\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\)
In both formulas, \(v\) is the image distance and \(u\) is the object distance.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the standard definitions of the variables used in the thin lens formula.

Step 2: Key Formula or Approach:
The lens formula is:
\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]

Step 3: Detailed Explanation:

• The thin lens formula establishes a relationship between the focal length of the lens, the distance of the object from the lens, and the distance of the image from the lens.

• By standard convention in optics:
- \(f\) represents the focal length of the lens (positive for convex, negative for concave).
- \(v\) represents the image distance, which is the distance from the optical center of the lens to the position of the image.
- \(u\) represents the object distance, which is the distance from the optical center of the lens to the position of the object.

• Matching these standard definitions with the options, Option (B) is correct.


Step 4: Final Answer:
The correct terms are: f = focal length, v = image distance, u = object distance.