A convex lens has a focal length of 20 cm. If an object is placed 60 cm from the

Practice Questions

Q1
A convex lens has a focal length of 20 cm. If an object is placed 60 cm from the lens, what is the distance of the image from the lens?
  1. 15 cm
  2. 30 cm
  3. 45 cm
  4. 60 cm

Questions & Step-by-Step Solutions

A convex lens has a focal length of 20 cm. If an object is placed 60 cm from the lens, what is the distance of the image from the lens?
  • Step 1: Identify the given values. The focal length (f) of the lens is 20 cm, and the object distance (u) is 60 cm.
  • Step 2: Use the lens formula, which is 1/f = 1/v - 1/u.
  • Step 3: Substitute the known values into the lens formula. This gives us 1/20 = 1/v - 1/60.
  • Step 4: Rearrange the equation to solve for 1/v. This means 1/v = 1/20 + 1/60.
  • Step 5: Find a common denominator to add the fractions. The common denominator for 20 and 60 is 60.
  • Step 6: Rewrite 1/20 as 3/60. Now the equation is 1/v = 3/60 + 1/60.
  • Step 7: Add the fractions: 3/60 + 1/60 = 4/60.
  • Step 8: Now, we have 1/v = 4/60. To find v, take the reciprocal: v = 60/4.
  • Step 9: Calculate 60/4, which equals 15 cm. Therefore, the distance of the image from the lens is 15 cm.
  • Lens Formula – The lens formula relates the focal length (f), the object distance (u), and the image distance (v) in a lens system, expressed as 1/f = 1/v - 1/u.
  • Convex Lens Properties – A convex lens converges light rays and can produce real and virtual images depending on the position of the object relative to the focal length.
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