1. The problem statement, all variables and given/known data 1: A decrease in the aperture of a lens changes the (A)Size of the image (B)Intensity of the image (C)Portion of the image (D) All of these 2: A vessel is filled with two different liquids which do not mix. One liquid is 40cm deep and has n=1.6 and the other is 30cm deep and has n=1.5. What is the apparent depth of the vessel when viewed along the normal? 2. Relevant equations 1: None 2: n=real depth/apparent depth 3. The attempt at a solution 1: The first ones answer is supposed to be (B)Intensity of the image. I don't know what intensity of an image is though, and I googled it but nothing came up. My answer would've been (C)Portion of the image, but I don't know what that exactly means either, but I'm assuming it means how much of the image you can see, and since the aperture decreases, that should decrease too. 2: This one is really weird an I have no idea how to solve it. The solution is- n1 = 1.6, d1 = 40 cm n2 = 1.5, d2 = 30 cm Apparent depth d = ? n = real depth (D)/apparent depth (d) ⇒ d = D/n = d1/n1 + d2/n2 d = (25 + 20) cm = 45 cm But how do they get d = D/n = d1/n1 + d2/n2? They have a video which goes into a bit more detail but I still don't get it :/ Could someone explain?