Skip to content
Login Register

#optical power

4 public questions tagged with this topic.

Combination of Lenses and Lens Systems

A convex lens (\( f = 60 \, \text{cm} \)) and a concave lens (\( f = 30 \, \text{cm} \)) are in contact. What is the eff

**Combination of lenses in contact** effective power P = P₁+P₂, effective focal length 1/F = 1/f₁ + 1/f₂, for thin lenses in contact. If separated by d, 1/F =1/f₁+1/f₂ - d/(f₁ f₂). Power adds algebraically, converging + with diverging - can cancel, used to correct aberrations and design achromatic doublets. f₁ = 60 cm , f₂ = -30 cm . (1/f) = (1/f₁) + (1/f₂) = (1/60) + (1/-30) = (1/60) - (2/60) = (1 - 2/60) = (-1/60) . f = -60 cm (diverging system). Substituting values gives -60 cm, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v -

Ref: NCERT > Physics Book > Ray Optics > Combination of Lenses and Lens Systems

View Details
Combination of Lenses and Lens Systems

A convex lens (\( f = 30 \, \text{cm} \)) and a concave lens (\( f = 15 \, \text{cm} \)) are in contact. What is the eff

**Two lenses in contact** behave as single lens with power sum, magnification product m = m₁×m₂. For f₁=20 cm (P₁=5 D), f₂=-20 cm (P₂=-5 D) in contact, P=0, F infinite, afocal system, beam emerges parallel, principle of corrective lenses for myopia/hypermetropia. f₁ = 30 cm , f₂ = -15 cm . (1/f) = (1/f₁) + (1/f₂) = (1/30) + (1/-15) = (1 - 2/30) = (-1/30) . f = -30 cm (diverging system). Substituting values gives -30 cm, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction

Ref: NCERT > Physics Book > Ray Optics > Combination of Lenses and Lens Systems

View Details
Optical Instruments - Simple and Compound Microscope

A telescope has an objective of focal length \( 100 \, \text{cm} \) and an eyepiece of focal length \( 5 \, \text{cm} \)

**Microscope principle** objective of short focal length forms real image between F_e and 2F_e of eyepiece, eyepiece magnifies to virtual image at D, total magnification product, for f_o=2 cm, f_e=5 cm, L=20 cm, m_o≈10, M_e≈6, M≈60, illustrating high magnification from two stages. Magnifying power: m = (f_o/f_e) . f_o = 100 cm , f_e = 5 cm . m = (100/5) = 20 . Substituting values gives 20, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction principles.

Ref: NCERT > Physics Book > Ray Optics > Optical Instruments - Simple and Compound Microscope

View Details