Question

10 cm is positive, if the value of object distance is:

• A. more than 10 cm
• B. more than 20 cm
• C. less than 10 cm
• D. none of these

Hint:

A concave mirror produces a virtual and magnified image when the object is placed between the pole and the focus.

Answer 1

The Correct Option is C

Step 1: Understanding magnification in a concave mirror.
The magnification (\( m \)) of a concave mirror is given by: \[ m = \frac{-v}{u} \] where:
- \( v \) is the image distance,
- \( u \) is the object distance.
For a concave mirror:
- If the image is real and inverted, the magnification is negative.
- If the image is virtual and upright, the magnification is positive.
Step 2: Condition for positive magnification.
- A concave mirror produces a positive magnification only when the image is virtual and erect.
- This happens when the object is placed between the focus (\( F \)) and the pole (\( P \)) of the mirror.
- The focal length of the mirror is given as 10 cm, meaning the focal point is at \( u = -10 \) cm.
Step 3: Finding the correct range for object distance \( u \).
- If the object is placed at \( u<10 \) cm (i.e., between the pole and focus), the image will be virtual, upright, and magnified.
- Hence, the correct answer is (C) less than 10 cm.