A lens forms a virtual image at a distance of 12 cm when the object is placed at 8 cm. What is the focal length of the lens?
Practice Questions
1 question
Q1
A lens forms a virtual image at a distance of 12 cm when the object is placed at 8 cm. What is the focal length of the lens?
4 cm
6 cm
8 cm
10 cm
Using the lens formula, 1/f = 1/v - 1/u, we find f = 4 cm.
Questions & Step-by-step Solutions
1 item
Q
Q: A lens forms a virtual image at a distance of 12 cm when the object is placed at 8 cm. What is the focal length of the lens?
Solution: Using the lens formula, 1/f = 1/v - 1/u, we find f = 4 cm.
Steps: 7
Step 1: Identify the given values. The object distance (u) is -8 cm (negative because it is on the same side as the object) and the image distance (v) is 12 cm (positive because it is a virtual image).
Step 2: Write down the lens formula: 1/f = 1/v - 1/u.
Step 3: Substitute the values into the lens formula: 1/f = 1/12 - 1/(-8).
Step 4: Calculate 1/12, which is 0.0833, and 1/(-8), which is -0.125. So, 1/f = 0.0833 + 0.125.
Step 5: Add the two fractions: 1/f = 0.0833 + 0.125 = 0.2083.
Step 6: To find f, take the reciprocal of 0.2083: f = 1/0.2083.
