BIO A person can see clearly up close but cannot focus on objects beyond 75.0 cm. She opts for contact lenses to correct her vision. (c) What focal length contact lens is needed, and what is its power in diopters?

Video transcript

Hi everyone in this practice problem, we're being asked to determine the focal length and also powers of contact lenses. We'll have an optometrist prescribes a con contact lens to adjust the vision of a student who encounters problems focusing on objects placed above one m. We are being asked to determine the focal length of the contact lens and also the power in diopters. The options given are a negative one m and what negative one diopter B negative 0.5 m and negative 0. diopters C 10.5 m and 2.0 diopters. And lastly D one m and 0.1 diopters. So we want this near sighted student to be able to see very distant objects clearly. That means that the contact lens must provide an image one m from the I or S prime will have to be equals to negative one m for equals to infinity or for an object that is located very far away. We want to employ the object image relationship for a lens where one divided by S plus one, divided by S prime will be equals to one divided by F F is the focal length S prime is the image distance and is the object distance we gonna substitute our S prime and infinity or just as value into our object image relationship in order to get the F or the focal length of our contact lens. So one divided by S will be one divided by infinity or essentially zero plus one, divided by S prime will be one divided by negative one of that will be equals to one divided by F or negative one m. So F will then equals to negative one m or F will equals to S prime. So uh after this, we can then determine that the contact lens is then divergent because the contact uh because the focal length is less than zero divergent because F is less than zero or negative. The power or the diopter can be determined by taking power will be equals to one divided by the focal length or F. So that will give us one divided by negative one m and that will give us a negative one diopters as the power. So there we have the focal length of the compact lens to be negative one m and we have the power in diopter to be negative one diopters. And that will give us option a to be the answer to this particular practice problem. So that will be it for this video. If you guys still have any sort of confusion, please make sure to check out our adolescent videos on similar topics. But other than that, that will be it for this one. Thank you.