Worksheet
SaitechAI — Objective Type Questions
Topic: Relation between focal length and radius of curvature, \( f=\dfrac{R}{2} \).
Assume magnitudes (ignore sign convention unless asked); write units.
Questions
- A spherical mirror has \( R=40\cm \). Find \( f \).
- Given \( R=1.2\m \). Find \( f \).
- The focal length is \( f=15\cm \). Find \( R \).
- For \( R=80\cm \), compute \( f \).
- If \( f=0.75\m \), compute \( R \).
- For \( R=24\cm \), compute \( f \).
- Given \( f=25\cm \), compute \( R \).
- State the relation between \( f \) and \( R \) for a spherical mirror (paraxial).
- If radius of curvature doubles, how does focal length (magnitude) change?
- For \( R=100\cm \), compute \( f \).
- If \( f=2\m \), compute \( R \).
- For \( R=30\cm \), compute \( f \).
Answer Key
- \(20\cm\)
- \(0.6\m\)
- \(30\cm\)
- \(40\cm\)
- \(1.5\m\)
- \(12\cm\)
- \(50\cm\)
- \( f=\dfrac{R}{2} \) (equivalently \( R=2f \))
- It doubles.
- \(50\cm\)
- \(4\m\)
- \(15\cm\)
Tip: Always keep units consistent; convert \( \mathrm{cm} \leftrightarrow \mathrm{m} \) when needed.