What is Focal: Definition and 292 Discussions

The HP-41C series are programmable, expandable, continuous memory handheld RPN calculators made by Hewlett-Packard from 1979 to 1990. The original model, HP-41C, was the first of its kind to offer alphanumeric display capabilities. Later came the HP-41CV and HP-41CX, offering more memory and functionality.

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  1. S

    Focal Length of a Plano-convex Lens

    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...
  2. L

    Negative Focal Length and Convex Mirrors: Is 1/di Negative?

    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...
  3. L

    Help_How to use graph to find focal length?

    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...
  4. I

    Telescope focal length homework

    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...
  5. P

    Graphing conves lense relationships to find focal lenght with slope

    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...
  6. G

    Difference between focal length and the distance from the lens

    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...
  7. D

    Contact lenses, focal length and uncorrected far point distance

    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!
  8. A

    Elliptical orbits and focal points

    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...
  9. T

    Therefore, the focal length of the mirror is -1m.

    [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...
  10. D

    Effective focal length of two plano convex

    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...
  11. F

    Focal Length & Position of an object.

    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...
  12. K

    How Do You Calculate the Focal Length of a Microscope's Eyepiece?

    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...
  13. M

    Potential temperature of a fresnel lens focal point

    Hi, I have a fresnel lens from a old big screen tv and it is roughly 1 meter square. The focal point comes down to roughly 2.5cm square (1"). On a sunny day in Hawaii I can melt copper wire after about a minute. Copper has a melting point of 1083°C (1981.4 °F) . That's some serious fun! I...
  14. Q

    Is 0.03 a Correct Focal Length Calculation for a 13 Field of View?

    Hi. If using: f (focal length) = a / ( 2 x arctan (theta / 2)) where a = 13 and is the Field of View the value I get for the focal length is 0.03 and this seems too small. Unless the calculation has not been done right? Thanks.
  15. W

    Objective Back focal plane diameter

    Hi, Have a query on the back focal plane diameter of an objective. I have got an equation back focal diameter = 320mm X NA / M where NA is the numerical aperture and M is the magnification. Just wondering is there any explanation for it? Thanks
  16. Q

    Calculating Projector Focal Length with SXGA & Screen Dimensions

    Hi. It asks to calculate the focal length range of a projector of square pixel SXGA is from 4 to 12 m from the screen. It gives the diagonal size of the display (in mm) as well as the horizontal size (in m). The thing that am not sure about is how the focal length would be calculated with the...
  17. W

    Calculating Focal Length of a Converging Lens Using Object and Image Distances

    Lens -- find the focal length 1. An object 3.0 cm tall is placed 20 cm in front of a converging lens. A real image is formed 10 cm from the lens. What is the focal length of the lens? 2. 1/f = 1/do + 1/di 3. 1/f = 1/do + 1/di 1/f = 1/20 + 1/10 f = 6.667 cm...
  18. H

    What Should Be the Focal Length of Kat's Corrective Contact Lenses?

    Homework Statement Without her contact lenses, Kat cannot clearly see an object more than 70.0cm away. What should be the focal length of her corrective contact lenses?Homework Equations 1/f = 1/p + 1/qThe Attempt at a Solution 1/f = 1/infinity + 1/-70.0cm = -0.0143cm f = -70.0 cm Would anyone...
  19. I

    Lenses and optics: solving for focal point.

    Lenses and optics: solving for focal point. (SOLVED) (2 points, penalty of 0.5) When a flower pot is placed 1.2 meters on the left of a magnifying glass (converging lens), an image is formed on a screen 0.37 meters to the right of the lens. Find the focal length of the lens. Give your answer...
  20. P

    What Is the Focal Length of Veronique's Glasses for Clear Vision?

    Homework Statement Veronique is nearsighted; she cannot see clearly anything more than 6.50 m away without her contacts. One day she doesn't wear her contacts; rather, she wears an old pair of glasses prescribed when she could see clearly up to 8.00 m away. Assume the glasses are 2.0 cm from...
  21. P

    Focal length of her contact lenses

    Homework Statement Anne is farsighted; the nearest object she can see clearly without corrective lenses is 2.4 m away. It is 1.8 cm from the lens of her eye to the retina. What should the focal length of her contact lenses be so that she can see clearly objects as close as 24.0 cm from...
  22. A

    Focal Length of Eye Homework: C, F Calcs & Myopia/Hyperopia

    Homework Statement The diagram shows the eye of a person with normal vision looking at an object that is very far away. a) Determine the focal length of this persons eye. b) Later in this person's life, the focal length will change to between 2.1 cm and 2.3 cm. Will this person suffer from...
  23. K

    What is the focal length of the lens?

    Homework Statement When a diverging lens is held 12 cm above a line of print, as in Figure 26.29, the image is 4.1 cm beneath the lens. What is the focal length of the lens? Homework Equations 1/di + 1/do = 1/f The Attempt at a Solution 1/di + 1/do = 1/f 1/4.1 + 1/12 = 1/f f =...
  24. I

    Focal Length and Lens Thickness: Exploring the Relationship

    Hi All! Im a bit confused regarding the relationship between focal length and the thickness of a lense. In the lab that we performed, my data seems to be skewed and I am unable to decipher the trend. Can someone explainwhat happens to the focal length as the thickness of the lenses...
  25. L

    Find the change in focal length

    Homework Statement A nearsighted person has eyeglasses with a -1D prescription. If the near point is at 23 cm without eyeglasses, where is it when they are put on? Homework Equations (1/f)=(1/do)+(1/di) The Attempt at a Solution I got the answer which is 0.298701298 meters by...
  26. A

    Exploring the Focal Point of a Concave Mirror

    I know that when the focal point is in the inside of a concave mirror. The focal point is greater than zero, and the radius is greater than zero and the lateral magnification is greater than zero. So if the focal point is on the outside of this concave mirror. Would the focal point be...
  27. D

    Focal Length of a Diverging Lens

    Homework Statement An object that is 6.00 cm tall is placed 40.0 cm in front of a diverging lens. The magnitude of the focal length of the lens is 20.0 cm. Find the image position and size. Is the image real or virtual? Upright or inverted? Homework Equations / The Attempt at a...
  28. Y

    Spherical mirror, shortest longest focal length

    hi again. i totally rocked my physics homework this week, except for this last one. Homework Statement Consider a spherical mirror without making the paraxial approximation (Fig. 36-47, attached as a file). When a ray parallel to the axis makes an angle θ with the radius R at the point of...
  29. R

    Determine the focal length of a lens

    Homework Statement A 2.0-cm-diameter spider is 2.0 {\rm m} from a wall. Determine the focal length of a lens that will make a half-size image of the spider on the wall. Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the wall...
  30. B

    Focal Length experiment readings

    Hello, I need help with the lens experiment, the aim of which is to determine the focal length of a concave lens by combining it coaxially with a convex lens. Given the focal length of the CONVEX lens is 15cm. and the focal length of the CONCAVE lens is 30cm. Can you give me a set of...
  31. J

    What is the mirror's focal length?

    A concave mirror creates an image on the screen 2x larger than the object. Both objects and screen are subsequently moved in order to create an image on the screen 3x larger than the object. 1) If the screen is moved 0.75 m in this process, how far is the object also moved? 2) What is the...
  32. N

    Solving Inverted Image w/Concave Mirror: 22 cm, 44 cm, & Focal Length

    Homework Statement An inverted image is magnified by 2 when the object is placed 22 cm in front of a concave mirror. Determine the image distance and the focal length of the mirror. Homework Equations don't have,sorry The Attempt at a Solution firstly,i use M= -di/do then i got...
  33. G

    What Is the Focal Length of the Lens When the Nickel's Image Doubles in Size?

    Homework Statement The nickel's image in the figure below has twice the diameter of the nickel when the lens is 2.90 cm from the nickel. Determine the focal length of the lens. Homework Equations M = h'/h = - (p/q) The Attempt at a Solution i don't really know how to start this...
  34. H

    Focusing on Object K: Magnification & Adjustment of Focal Length

    Homework Statement Suppose the lens in a human eye has far focal length equal to f0 = 40.1 mm, for distant objects to be in focus. A. An object K is 1.69 m from the lens. How much should the focal length change to focus on the object K? B.What is the magnification ( = image size...
  35. S

    The focal length of a mirror. Help me maybe?

    Homework Statement Mastering physics problem 23.76 difficulty rating: two bars=difficult 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, 180cm from the object. What is the focal length of the mirror? Homework Equations...
  36. A

    Focal length of concave lens experiment

    Is there any way to find rough focal length of concave lens and convex mirror without using convex lens? Though I did the experiments(with object and image needles, not candle) very carefully with no parallax errors during my practical class, my readings are incorrect. I want to know if der s...
  37. S

    Lens and Focal Length Practice Problems

    Homework Statement A 2.0-cm-diameter spider is 1.80 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...
  38. G

    Lens & Focal Point System: Image Formation

    Homework Statement I have a two lens system (both are convex lens; converging lens). Say I set lens 1 on left hand side and lens 2 on the right hand side. A)If I place an object within the focal point of lens 1 and the image create by this lens is OUTside the focal distance of lens 2, what...
  39. G

    Creating an Image 2x Size of Object w/ Convex Lens: Half Focal Length Away

    Homework Statement A converging lens (convex lens) creates an image that is 2 times the size of the object. The object is placed: Homework Equations -di/do = hi/ho 1/f = 1/di + 1/do The Attempt at a Solution I thought the answer was that the object is place two focal lengths...
  40. J

    Find the focal length of a concave lens using a convex lens?

    Can anyone explain to me the procedure that one would follow to you find the focal length of a concave lens using a convex lens? Thanks.
  41. C

    Magnification and focal length

    Homework Statement A lens has a focal length of 120 cm and a magnification of 4.0. How far apart are the object and the image? Homework Equations I used the thin lens equation 1/f = (1/di + 1/do)^-1 and M = -d image/d objectThe Attempt at a Solution I have been trying this by rearranging the...
  42. I

    SK15075PEQ3-2- Diameter/Aperture: 150mm- Focal Length: 750mm-

    SK15075PEQ3-2 - Diameter/Aperture: 150mm - Focal Length: 750mm - Diffraction-limited secondary mirror support - Paraboloidal (parabolic) primary mirror - 150 primary mirror gathers enough light to reveal deep-sky luminaries. 33% more light gathering power than 130mm, 73% more light than...
  43. A

    Positive Focal Length Image - Real, Diminished, Inverted and Smaller?

    This is a simple wording confusion. On one question that I did, the property for a positive focal length image was Real, Diminished and Inverted. On another question of the same type, the property for a positive focal length image was Real, Inverted and Smaller. So, my confusion is the...
  44. rohanprabhu

    Associating a focal length to an angle for a parabola

    Homework Statement If there is a line from the focus of a parabola such that it makes an angle \theta with the x-axis. It intersects the parabola at a point 'P'. I want to find the focal length of the point P as a function of \theta. The Attempt at a Solution The equation of the parabola is...
  45. A

    Locating Image on Retina with Focal Length 0.020m

    Homework Statement This is a follow on question. The first few questions ask about finding the numerical answer. The question that I am confused about and cannot do seem to do properly says: Complete the ray diagram to locate the position of the image shown on the retina when effective focal...
  46. E

    Spot size and focal length lens

    why does the spot size increase with lower f#. Lets says you have 2 lens of the same material, and diameter, just different focal length. F/2 has higher spot size than F/3 but F/2 is faster. Is spot size a characteristic of a lens? So if your detector is fixed in size you need to get a lens...
  47. X

    Determining Focal Length of Convex Lens Without Apparatus

    So I got a lab to plan and design an experiment to determine the focal length of a convex lens and involve the use of lens eq. and by means of plotting a graph...I have a basic rundown of what needs to be done and all but I am somewhat in a dilemma i don't have any access to any of the apparatus...
  48. M

    What are uses for lens focal points?

    Can you tell me the need & use of the pocal points on a lens , why do we need to have them , why do we measure them . focal points can be used for various measurements but other than that ?
  49. J

    Calculating Focal Length for Presbyopia Glasses

    Homework Statement A person with presbyopia can see distant objects clearly, but is unable to accomadate to see near objects because of hardening lens. one person cannot see objects nearer than 1.5m. a)the focal length of the eye glasses needed to see objects as close as 25cm. Homework...
  50. R

    2 focal points, find image distance.

    Homework Statement An object is placed in front of a converging lens in such a position that the lens (f = 15.0 cm) creates a real image located 21.0 cm from the lens. Then, with the object remaining in place, the lens is replaced with another converging lens (f = 16.0 cm). A new, real image...
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