An object is placed 40 cm from a convex lens with a focal length of 10 cm. Where

Practice Questions

Q1
An object is placed 40 cm from a convex lens with a focal length of 10 cm. Where is the image formed?
  1. At 10 cm
  2. At 20 cm
  3. At 30 cm
  4. At 40 cm

Questions & Step-by-Step Solutions

An object is placed 40 cm from a convex lens with a focal length of 10 cm. Where is the image formed?
  • Step 1: Identify the given values. The object distance (u) is -40 cm (negative because it is on the same side as the object) and the focal length (f) is +10 cm (positive for a convex lens).
  • Step 2: Use the lens formula: 1/f = 1/v - 1/u, where v is the image distance.
  • Step 3: Substitute the values into the lens formula: 1/10 = 1/v - 1/(-40).
  • Step 4: Simplify the equation: 1/10 = 1/v + 1/40.
  • Step 5: Find a common denominator for the right side, which is 40v: 1/10 = (4 + v)/(40v).
  • Step 6: Cross-multiply to solve for v: 40v/10 = 4 + v.
  • Step 7: Simplify the equation: 4v = 4 + v.
  • Step 8: Rearrange the equation: 4v - v = 4, which gives 3v = 4.
  • Step 9: Divide both sides by 3 to find v: v = 4/3 cm, which is approximately 1.33 cm.
  • Step 10: Since the image distance is positive, the image is formed on the opposite side of the lens.
  • Lens Formula – The lens formula relates the object distance (u), image distance (v), and focal length (f) of a lens: 1/f = 1/v - 1/u.
  • Convex Lens Properties – A convex lens converges light rays and can form real or virtual images depending on the object's position relative to the focal length.
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