If a lens forms a real image at a distance of 40 cm from the lens, and the object is placed at 60 cm, what is the focal length of the lens?
Practice Questions
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Q1
If a lens forms a real image at a distance of 40 cm from the lens, and the object is placed at 60 cm, what is the focal length of the lens?
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Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/40 - 1/(-60) = 1/40 + 1/60 = 1/24. Therefore, f = 24 cm.
Questions & Step-by-step Solutions
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Q
Q: If a lens forms a real image at a distance of 40 cm from the lens, and the object is placed at 60 cm, what is the focal length of the lens?
Solution: Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/40 - 1/(-60) = 1/40 + 1/60 = 1/24. Therefore, f = 24 cm.
Steps: 9
Step 1: Identify the given values. The image distance (v) is 40 cm and the object distance (u) is -60 cm (negative because the object is on the same side as the incoming light).
Step 2: Write down the lens formula: 1/f = 1/v - 1/u.
Step 3: Substitute the values into the lens formula: 1/f = 1/40 - 1/(-60).
Step 4: Simplify the equation: 1/f = 1/40 + 1/60.
Step 5: Find a common denominator to add the fractions. The common denominator of 40 and 60 is 120.
Step 6: Convert the fractions: 1/40 = 3/120 and 1/60 = 2/120.
