Focal Definition and 279 Threads

Hi guys! I face some difficulty in finding the focal length of a microlens. Assuming that the microlens is spherical, and the medium of the surrounding is vacuum. I really need an equation to get me going for my research task. I actually found the lensmaker's equation which is /=(−)(/−/+(−)/...

Homework Statement Following data recorded: Di (distance image to lens) 6.0 8.0 10.0 12.0 14.0 Magnification 0.2 0.6 1.0 1.4 1.8 Graph magnification against di and use the graph to find the focal length of the lens. Homework Equations...

Homework Statement A patient is unable to see objects closer than 1m from the eye. Calculate the focal length of the converging lens which is required to reduce this to 25cm. Homework Equations Lensmaker's equation: 1/u + 1/v = 1/f u= distance from object to lens v= distance of...

length. I was asked to find the image and the object distance. I didnt think it was possible till i found this M=h'/h=-q/p : I knew this q=-ph'/h : I understood how they did this 1/p+1/q=1/f : I knew this 1/p+1(-ph'/h)=-1/f : This i understood also, but how they came up with...

What is the longest focal length practical for a lens and/or shaped mirror? I ask because it would be good if we could put a mirror at GEO and shine sunlight at one spot on the Earth 24 hours per day for energy production. The problem is sunlight is dispersing 1% so from 36,000km it would...

Homework Statement I have an actually interesting practical homework. I need to calculate the optical strength (hope I translated it right, D=1/F), to do I need to find the lens focal length. I need to find my self a concave and a convex lens. I don't have a concave lens (I think), but I do...

Homework Statement Find focal length for meniscus convex (3) Given r = 15, and n = 1.5 Homework Equations Lens maker's equation The Attempt at a Solution I can find the rest except #3 and #6 (they are opposite sign of each other) I had (1/r1 - 1/r2) gives zero... which is wrong... I...

A magnifying glass has a diverging lens with a 13.0 cm focal length. At what distance from a toothpick should you hold this lens to form an image with a magnification of +5.00? I simply have no idea what to do. I tied moving around the equations to make them work, but I can't figure it out...

Homework Statement A 2.0 cm tall object is placed in front of a mirror. A 1.0 cm tall upright image is formed behind the mirror, 165 from the object Homework Equations 1/s + 1/s' = 1/focal length h' / h = magnification -s' / s = magnification h' / h = s' / s (i found this...

Homework Statement I must calculate the focal length of a GRIN lens. I.e. a lens which radii of curvature are both infinite. I will consider the refractive index to be varying in function of y (the height in the x-y plane). Say I'm given that at y=0, n(0)=n_0. I'm not sure how to write...

Homework Statement http://img256.imageshack.us/img256/6330/35727193.jpg Homework Equations [PLAIN]http://upload.wikimedia.org/math/2/0/a/20aa1e3d192ecb3164ac4f2095c86cd3.png The Attempt at a Solution i have used triangle from up side of h1 to the b. and by using sinß and...

Homework Statement What is the focal length of a drop of water in the form of a sphere with radius 4mm given that the refractive index of water = 4/3 Homework Equations The Attempt at a Solution Here, i think i will need to assume that the light rays are coming from infinity...

After using the equation 1f = 1÷do + 1÷di I found what the focal point / f was. Now, what would the focal point represent? Is the focal point the image height or object height in the equation m = hi÷ho = -di÷do

1)Why when a convex lens having radius of curvature R, focal length f and refractive index μ is bisected horizontally along the principal axis its focal length remains the same, whereas when it is bisected vertically focal length becomes 2f? Does the same thing happens in the case of...

Why is a telephoto lens considered to have a longer focal length than that of single convex lens?

1. Why is a telephoto lens considered to have a longer focal length than that of a single convex lens? A lens combination, such as a diverging and a convex lens, is referred to as a telephoto lens. Suggest why a telephoto lens is considered to have a longer focal length than that of a single...

1. Why is a telephoto lens considered to have a longer focal length than that of a single convex lens? A lens combination, such as a diverging and a convex lens, is referred to as a telephoto lens. Suggest why a telephoto lens is considered to have a longer focal length than that of a single...

Homework Statement An object is placed in front of a concave mirror, 15.0 cm from the mirror's focal point. The image formed by the mirror is five times farther away from the focal point. Calculate the focal length of the mirror. There are actually two possible image distances di that...

Hello, all, I am using 9 fresnel lenses (~1x1' per lens) and 9 water blocks for a solar water heater. Each fresnel lens is positioned so that a water block below is heated. A pump is used to pump the water through the system. However, I have one question... I have all of my fresnel...

Homework Statement A slide projector needs to create a 81 cm high image of a 2.0 cm tall slide. The screen is 360 cm from the slide. Assume that it is a thin lens. What focal length does the lens need? How far should you place the lens from the slide? Homework Equations 1/f = 1/s +...

Homework Statement A Lens maker desires to make a lens of focal length 30 cm. in air. The equipment in the shop is set to make lens faces of 20 cm. a. What index of refraction should the lens material have to produce this focal length? b. What would the focal length of this lens be...

Hey Guys, first of all I apologise if this question is posted in the wrong forum section and a mod has to move it to its correct location. I am trying to find information on combining the paths of several laser beams. I have found much complex information pertaining to the combination of the...

Homework Statement Hey,, I was wondering if anyone could help me with some physics work i am doing as i am completely stuck. Is there supposed to be any relationship with the magnification and focal length of lenses and if so what is it? I did an experiment and measure the magnification of...

Hello, I wanted to ask, is it possible for a magnetic lens to have many focal points, when the magnetic field of the lens is sufficiently large? if so what is the reason for this? how does this give better resolution of images compared to a simple optical lens. I know for a normal optical lens...

The homework problem is "An object 26.0 cm in front of a certain lens is imaged 1.60 cm in front of that lens (on the same side as the object). What is the focal length (in centimeters) of this lens" 1/f = 1/di + 1/do I tried solving based on having distance of object (do) and...

I understand completely how to go about doing this problem... I know that you would have to plot the points and draw a line of best fit and that the x-intercepts and y-intercepts would equal 1/f... but what would the actual focal length be? and how do you calculate the gradient? This is actually...

What is the focal length of a thin, flat piece of glass with no curvature? I found that the power is 0 diopters, but I don't know what the focal length is.

Homework Statement An optical system consists of two identical lenses; the focal length of each lens is fo (where fo) is positive). The lenses are separted by a distance d. Denote the focal lenths of the lens assembly by f and f'. a) Show that for any separation of the lenses f = f'...

Homework Statement An object is located 26.0cm from a certain lens. The lens forms a real image that is twice as high as the object. (i) What is the focal length of this lens? (ii) Now replace the lens used in Part 1 with another lens. The new lens is a diverging lens whose focal...

Homework Statement A building will be photographed with a camera. The distance is 490 m to the building. The building height is 85m and width 40m. You can choose between 35mm, 50mm, 135mm and 250mm lenses (focal length of lenses). Select the lens that gives the largest image of the building...

Homework Statement A small object is 25.0 cm from a diverging lens as shown in the figure . A converging lens with a focal length of 11.4 cm is 30.0cm to the right of the diverging lens. The two-lens system forms a real inverted image 17.0 cm to the right of the converging lens. The...

Homework Statement When using the lens formula: 1/f = 1/u + 1/v for someone who has short sightedness and cannot focus on objects on objects more than 2.5m away, I get: 1/f = 1/infinity + 1/-2.5 f = -2.5 mIf using the formula for someone who had long sightedness and could not focus on...

Homework Statement An object is located 27.5 cm from a certain lens. The lens forms a real image that is twice as high as the object. b) Now replace the lens used in Part A with another lens. The new lens is a diverging lens whose focal points are at the same distance from the lens as the...

The distance between an object and its upright image is 15.5 cm. If the magnification is 0.7, what is the focal length of the lens being used to form the image? Answer in units of cm. So I tried combining the equations p+q=15.5 and -q/p=.7 and still was unable to come up with a correct...

An object 5 cm tall is 10 cm from a convace lens. The resulting image is one fifth as large as the object. What is the focal length of the lens? I have been doing questions involving focal lenght, but not when the resulting image is a fraction of the original image. i do not know where to...

I'd like to ask does thinner convex lens give a shorter focal length? If so, why is it? thanks very much~~

Let's say that there are three lenses A (all of which are semicircles: flat on one side, curved on the other). One lense is a short and curved D, another lense is a very elongated and narrow D (longer than the first lense), and the third lense is as long as the second lense but has a sharper...

Let's say that there are three lenses A (all of which are semicircles: flat on one side, curved on the other). One lense is a short and curved D, another lense is a very elongated and narrow D (longer than the first lense), and the third lense is as long as the second lense but has a sharper...

The given problem: What is the focal length of a Plano-convex lens, assuming parallel rays of light from s=∞ is traveling from the flat end of the lens. The lens is a glass hemisphere of radius R. Additionally the index of refraction of glass is higher than that of air. Homework...

Hey, When dealing with convex mirrors I know that the image will always be virtual,upright and diminished. So when I am using descartes's formulae i know that for convex mirrors that the focal length is negative, but does my 1/di become negative? because virtual images have a negative height...

Homework Statement Rearrange the lens equation to make 1/v the subject of the equation and then write it as a linear equation. This will lead you to a possible graph for data of object distances and image distances from which you will be able to evaluate the focal length f of the convex lenses...

Hey guys, I am really stuck on my homework review and really require help! Someone please help ! :( Homework Statement Question 1: A telescope has a focal length of 18m. If the suns diameter is about 1.39 x 10^9m and its distance from Earth is 1.49 x 10^11, how large is the telescopes image...

Homework Statement I need to find the relationship between object-lens distance and image-lens distance for a lense(converging) but cannot graph the relationship in a way that the focal length is the slope for the graph Homework Equations 1/u + 1/v = 1/f where u= object lense distance...

Lens and distances I do use images as help when working theses out. going to try and scan theses in but tryed my best just using pc for now. 0 = lens F = focal length 1) a camera with a 50mm focal length lens is focused on a persons face 1m from the lense. show that the film will be about...

1. A nearsighted person wears contacts with a focal length of -7.6cm. If this person's far point distance with her glasses is 8.7m, what is her uncorrected far point distance? 2. 1/F=1/do+1/di 3. 1/-7.6=1/do+1/870 =-7.534 I am completely lost here...please help. Thanks!

I was recently studying elliptical orbits and the precession of the perihelion of Mercury. I remembered from my pre-calc class that all ellipses have two focal points. In this case the obvious would be the Sun as on focal point for all the planets, but where would the second be? I have a...

[SOLVED] Focal length of a mirror Homework Statement A 2.0-cm-tall object is placed in front of a mirror. A 1.0-cm-tall upright image is formed behind the mirror, 150 cm from the object. What is the focal length of the mirror? Homework Equations 1/f=1/s+1/s' m=h'/h m=-s'/s...

Homework Statement Hello Two plano convex with f1=f2=30mm and R1=15.45mm and R2=-R1. The two plano convex have the same thickness too (3.16 mm) and their curves colide in the propagation axis. I believe you understand what i mean What is the focal length of the two plano convex system...

Homework Statement A 2.0-cm-diameter spider is 3.0 m from a wall. (a) Determine the focal length of a lens that will make a half-size image of the spider on the wall. (b) Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the...

Homework Statement The near point of a naked eye is 25 cm. When placed at the near point and viewed by the naked eye, a tiny object would have an angular size of 5.2X10-5 rad. When viewed through a compound microscope, however, it has an angular size of -9.20X10-3 rad. (The minus sign...