A parallel beam of light ray parallel to the x-axis is incident on a parabolic reflecting surface as shown in the figure. After reflecting it passes through focal point F. What is the focal length of the reflecting surface?
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Official Solution
Correct Option: (2)
Step 1: Concept
The standard equation of a parabola is , where is the focal length. Step 2: Analysis
Given equation: , which can be rewritten as . Step 3: Calculation
Comparing with :
.
Solving for : . Step 4: Conclusion
Hence, the focal length is . Final Answer:(B)
