virtual image

Examples of virtual image in the following topics:

• Image Reflection by a Plane Mirror

  • A mirror is a reflective surface that bounces off light, thus producing a real or virtual image.
  • An image formed by reflection may be real or virtual.
  • A "virtual" image occurs when light rays do not actually meet at the image.
  • A virtual image is right side up (upright).
  • These diagrams can be used to find the position and size of the image and whether that image is real or virtual.

• Image Formation by Spherical Mirrors: Reflection and Sign Conventions

  • This image that appears to be behind the mirror is called the image.
  • An image formed by reflection may be real or virtual.
  • A virtual image occurs when light rays do not actually meet at the image.
  • A virtual image is right side up (upright).
  • For a convex mirror, the image is virtual and upright.

• The Telescope

  • The image is focused at point 5, and the observer is shown a brighter, magnified virtual image at point 6.
  • Reflecting telescopes, such as the one shown in , use either one or a combination of curved mirrors that reflect light to form an image.
  • (The distance from the mirror to the focal plane is called the focal length. ) A sensor could be located here to record the image, or a secondary mirror could be added to redirect the light to an eyepiece.
  • Catadioptric telescopes, such as the one shown in , combine mirrors and lenses to form an image.
  • The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye is able to collect on its own, focus it 5, and present the viewer with a brighter, clearer, and magnified virtual image 6.

• Holography

  • Holography is an optical technique which enables three-dimensional images to be made.
  • Holography is a technique which enables three-dimensional images to be made.
  • The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional.
  • The image this effect produces in a person's retina is known as a virtual image.

• Combinations of Lenses

  • Note the sign convention: a telescope with two convex lenses (f1 > 0, f2 > 0) produces a negative magnification, indicating an inverted image.
  • A convex plus a concave lens (f1 > 0 >f2) produces a positive magnification and the image is upright.
  • The lens is more powerful for violet (V) than for red (R), producing images with different locations and magnifications.
  • The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye could collect on its own, focus it 5, and present the viewer with a brighter, clearer, and magnified virtual image 6.

• Further Reading

  • To learn more about bremsstrahlung and virtual quanta, consult Chapter 15 of

• NMR and MRIs

  • Magnetic resonance imaging is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
  • Magnetic resonance imaging (MRI), also called nuclear magnetic resonance imaging (NMRI) or magnetic resonance tomography (MRT), is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
  • MRI utilized the property of nuclear magnetic resonance (NMR) to image the nuclei of atoms inside the body.
  • MRI shows a marked contrast between the different soft tissues of the body, making it especially useful in imaging the brain, the muscles, the heart, and cancerous tissue—as compared with other medical imaging techniques such as computed tomography (CT) or X-rays.

• Nearsightedness, Farsidedness, and Vision Correction

  • In order for the human eye to see clearly, the image needs to be formed directly on the retina; if it is not, the image is blurry.
  • When the image finally reaches the retena, it is inverted, but the brain will correct this .
  • For the vision to be clear, the image has to be formed directly on the retina.
  • Farsightedness, or hyperopia, is a vision defect that occurs when the focus of the image is behind the retina.
  • Rays from the top and bottom of the object are traced and produce an inverted real image on the retina.

• Emission Topography

  • Positron emission tomography is a nuclear medical imaging technique that produces a three-dimensional image of processes in the body.
  • Positron emission tomography (PET) is a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body.
  • Three-dimensional images of tracer concentration within the body are then constructed by computer analysis.
  • Because PET imaging is most useful in combination with anatomical imaging, such as CT, modern PET scanners are now available with integrated high-end multi-detector-row CT scanners .
  • Because the two scans can be performed in immediate sequence during the same session, with the patient not changing position between the two types of scans, the two sets of images are more-precisely registered, so that areas of abnormality on the PET imaging can be more perfectly correlated with anatomy on the CT images.

• The Thin Lens Equation and Magnification

  • How does a lens form an image of an object?
  • We can also develop equations to describe the images quantitatively.
  • Ray tracing is used to locate the image formed by a lens.
  • The image is located at the point where the rays cross.
  • Shows how to use the thin lens equation to calculate the image distance, image height and image orientation for convex lenses when the object distance is greater the the focal length (f).