alleryStart learning →What is the focal length of a lens?
ADistance from one face of the lens to the other
BDistance from the object to the centre of the lens
CDistance from the centre of the lens to its focal point
DDistance from the focal point to the image position
Answer & Solution
Correct answer: C. Distance from the centre of the lens to its focal point
1. The focal length f is the distance from the centre of the lens to its focal point.
2. A thin symmetrical lens has two focal points, one on either side and both at the same distance from the lens.
3. The thickness of the lens is assumed negligible in the thin lens treatment, so it is not the focal length.
4. Object and image distances change as the object moves, while the focal length is fixed by the lens itself.
_Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.6 Image Formation by Lenses_
Keep practising Geometric Optics
Browse all Geometric Optics questions for CSEC (CXC), or explore more Physics topics.
Related questions
Complete the optics rulesMatch each optics termStack the optics termsSort real and virtual imagesPull the rope to the right lensA makeup mirror has a power of 1.50 D. What is its focal length?A camera maker wants to replace an 800 mm focal length telephoto lens with a mirror. What A convex mirror has a radius of curvature of 3.00 cm. What are its focal length and its po