Total Questions: 10
The amount of light entering into the eye can be controlled and regulated by the iris.
To find the power of a convex lens, we use the lens formula and the power formula. Let's solve this step by step. Given that
Image distance (v) = +20 cm (positive for a real image formed on the other side of the lens) Object distance (u) = -60 cm (negative as per the sign convention for the object distance) Focal length (f) needs to be calculated first, then power (P) will be derived. Step 1: Lens Formula The lens formula is: (1/f) = (1/v) - (1/u) (1/f) = (1/20) - (1/-60) Simplifying (1/f) = (1/20) + (1/60) = (4/60) = (1/15) So, the focal length f is: f=+15 cm (The positive sign indicates a convex lens.) Step 2: Power of the Lens The power P of a lens is given by: P=1/f (in meters) Convert the focal length from centimeters to meters: f = 15/100 = 0.15 m Now calculate the power: P = 1/0.15 = 10/1.5= 6.67 diopters (D)
Given that :
Object distance, u = −25 cm. Image distance, v = +20 cm. Lens formula: 1/f = (1/v) − (1/u) = (1/20) - (1/-25) = (1/20) + (1/25) = (5 + 4)/100 = 9/100 ∴ f = 100/9 cm Then P = 1/f (f in metres) = 1/100/(9 × 100) ⇒ 9 diopters
Object distance, u = −20 cm. Image distance, v = +16 cm. Lens formula: 1/f = (1/v) − (1/u) = (1/16) - (1/-20) = (1/16) + (1/20) = (5 + 4)/80 = 9/80 ∴ f = 80/9 cm Then P = 1/f (f in metres) = 1/80/(9 × 100) ⇒ (100 × 9)/80 ⇒ 11.25 diopters The power of the lens is positive.
Object distance, u = −40 cm. Image distance, v = +10 cm. Lens formula: 1/f = (1/v) − (1/u) = (1/10) - (1/-40) = (1/10) + (1/40) = (4+1)/40 = 5/40 ⇒ 1/8 cm ∴ f = 40/5 cm ⇒ 8 cm Then P = 1/f (f in metres) = 1/8/100 ⇒ (100)/8 ⇒ 12.5 diopters The power of the lens is positive.
Sand desert = 20-30% plain land = 25% Land covered by fresh snow = 85% Paddy cropland = 20-25%.
