A convex lens of power \( +4 \, \text{D} \) is used. What is its focal length?
**Power of lens** P (D) = 1/f (m), +5 D => f=1/5=0.2 m=20 cm. Virtual magnified image by convex lens when object within focal point, u
Ref: NCERT > Physics Book > Ray Optics > Thin Lenses - Lens Formula, Magnification and Power