n :-Two thin LENSES of power +2.5D and -0.5D are put in contact, what is the power, focal length of the combination?__________________Solution :-➲ Given Information :-Power of Lens 1 ( Power₁ ) ➢ +2.5 DPower of Lens 2 ( Power₂ ) ➢ -0.5 D➲ To Find :-Power of the combination ( Power₁ + Power₂ )Focal Length of the combination➲ Concept :-Simple numericals based on Refraction of Light through Lenses➲ Formulae USED :-\boxed{\boxed{\bf{\red{Power = Power_1 + Power_2}}}} Power=Power 1 +Power 2 \boxed{\boxed{\bf{\green{Focal\: Length = \dfrac{1}{Power}}}}} FocalLength= Power1 ➲ Explanation :-In order to find the power of the two lenses, We will add the power of each lens. The resultant will then be put in the formula mentioned above, used to calculate Focal Length. After some minute calculations, we'll have our answers, i.e., Power of the combination and Focal Length of the combination of lenses. So let's proceed towards our calculation.➲ Calculation :-Firstly Calculating the Power of the combination.Substituting the values given in the first formula, We get,\boxed{\boxed{\rm{\red{Power = Power_1 + Power_2}}}} Power=Power 1 +Power 2 Substituting the values, We get,\rm:\implies{\purple{Power = +2.5 \:D + ( - 0.5 \:D )}}:⟹Power=+2.5D+(−0.5D)\rm:\implies{\purple{Power = +2.5\: D - 0.5\: D }}:⟹Power=+2.5D−0.5D\rm:\implies{\purple{Power = \bf{+2.0 \:D}}}:⟹Power=+2.0D∴ The Power of the combination of lenses is 2.0 DNow calculating the Focal Length of the combination.Substituting the values given in the second formula, We get,\boxed{\boxed{\rm{\green{Focal\: Length = \dfrac{1}{Power}}}}} FocalLength= Power1 Substituting the values, We get,:\implies\rm{\blue{Focal\: Length = \dfrac{1}{2.0}}}:⟹FocalLength= 2.01 \because\:(\rm{\dfrac{1}{2.0}} \: can \:also \:be \:written \:as\: 0.5)∵( 2.01 canalsobewrittenas0.5)\rm:\implies{\blue{Focal\: Length = \dfrac{1}{2.0} = 0.5 \:m \: or\: 50\: cm}}:⟹FocalLength= 2.01 =0.5mor50cm∴ The Focal Length of the combination of lenses is 0.5 m or 50 cm____________________Final Answer :-The Power of the combination of lenses is 2.0 DThe Focal Length of the combination of lenses is 0.5 m or 50 cm____________________