Sunderdeep Pharmacy College Questions and Answers

Dear student,

You are asking if the focal length of a lens is 20 cm, what is its power in diopters?

Calculating Lens Power:

• Power of a lens is defined as the reciprocal of its focal length when expressed in meters
• The unit of power of a lens is diopter (D)

Formula:

• Power (P) = 1 / focal length (in meters)

Given:

• Focal length (f) = 20 cm = 0.2 meters

Calculation:

• Power (P) = 1 / 0.2 = 5 diopters

Therefore, the power of the lens is +5 diopters

Why is it positive?

• A positive power indicates a convex lens (converging lens)
• Convex lenses are thicker at the center and thinner at the edges
• They converge light rays to a point called the focus

convex lens

Additional Notes:

• Concave Lens: If the lens were concave (diverging lens), the power would be negative
• Units: Always ensure that the focal length is converted to meters before calculating the power in diopters

Therefore, if a lens has a focal length of 20 cm, its power is +5 diopters. This means it is a convex lens capable of converging light rays.

Dear Student,

Candidates can start early, create a strategy and have a structured schedule to level up their preparation. To effectively prepare for NEET candidates must follow the below given tips and a study schedule. 

• Understand the Exam Syllabus: Candidates must familiarise NEET syllabus and the marking scheme. 
• Craft a Study Plan: Students must allocate specific time slots for each subject and study in a similar schedule. 
• Read, Revise & Repeat: Candidates must schedule weekly revisions to check things that they have learnt and revise the last read chapters. 
• Practice Mock Papers: Candidates must regularly attempt mock tests and previous year's papers to keep a check on their preparation.
• Maintain a Healthy Lifestyle: Students must maintain a balanced diet and ensure adequate sleep to keep their minds sharp.

Further, candidates can follow the NEET 2025 Preparation Time Table and study for 7-8 hours everyday.

Thank You

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