13.4 Lenses and Image Formation

• Geometric optics assumes light travels in straight lines called rays.

  True
• Convex lenses have a positive focal length, while concave lenses have a negative focal length.


  True
• Wave optics considers the wave-like properties of light, such as interference and diffraction
• Convex lenses form virtual images, while concave lenses form real images.

  False
• Order the image characteristics based on object location in a convex lens:

  1️⃣ Beyond 2f: Real, inverted, diminished

  2️⃣ At 2f: Real, inverted, same size

  3️⃣ Between f and 2f: Real, inverted, enlarged

  4️⃣ At f: No image formed

  5️⃣ Between lens and f: Virtual, upright, enlarged
• What are principal rays in ray diagrams used to determine?

  Image position, size, orientation
• A central ray continues undeviated through the lens.


  True
• What does a positive image distance indicate for a convex lens?

  Real image
• One key assumption of geometric optics is that light travels in straight lines.
• What are lenses used to bend or refract?

  Light
• Match the concept with its description:

  Geometric Optics ↔️ Assumes light travels in straight lines

  Wave Optics ↔️ Considers the wave-like properties of light
• Order the key properties of convex and concave lenses:

  1️⃣ Focal Length: Positive (convex) or Negative (concave)

  2️⃣ Optical Power: Positive (convex) or Negative (concave)

  3️⃣ Image Formation: Real, inverted (convex) or Virtual, upright (concave)
• Wave optics uses ray diagrams to model light behavior.

  False
• Match the principal ray with its behavior in a convex lens:

  Parallel Ray ↔️ Refracts through the focal point

  Focal Ray ↔️ Refracts parallel to the optical axis
• Concave lenses always produce virtual, upright, and diminished images.


  True
• A ray parallel to the principal axis refracts through the focal point.
• Match the object position with the image formed by a convex lens:

  Beyond 2F ↔️ Real, inverted, diminished

  At 2F ↔️ Real, inverted, same size

  Between F and 2F ↔️ Real, inverted, magnified

  At F ↔️ No image formed
• For a concave lens, the image distance is always negative.

  True
• What type of image does a convex lens typically form?

  Real, inverted
• Convex lenses are thicker at the center
• Concave lenses form a virtual, upright image.
• What happens to a focal ray after it passes through the focal point of a convex lens?

  Refracts parallel to the optical axis
• What does the lens equation relate for a convex lens?

  Object distance, image distance, focal length
• What does a positive image distance (v) indicate for a convex lens?

  Real image
• The image distance (v) is positive for a real image and negative for a virtual image.
• Steps to rearrange the thin lens equation to solve for image distance (v)

  1️⃣ Start with the thin lens equation: $1 / f =$$1 / v +$$1 / u$

  2️⃣ Subtract $1 / u$ from both sides: $1 / v =$$1 / f - 1 / u$

  3️⃣ Simplify the right side by finding a common denominator

  4️⃣ Take the reciprocal of both sides to solve for v
• What is the thin lens equation used to calculate?

  Image distance
• What is the formula for magnification (m) in geometric optics?

  $m =$$v / u$
• Order the following object positions relative to a convex lens based on their magnification effects:

  1️⃣ Beyond 2f (diminished)

  2️⃣ At 2f (same size)

  3️⃣ Between f and 2f (enlarged)

  4️⃣ Between lens and f (enlarged)
• When an object is placed between f and 2f of a lens, the image is enlarged
• What is the magnification if the image distance is 15 cm and the object distance is -30 cm?

  -0.5
• What are the characteristics of real images?

  Inverted, enlarged or diminished
• Real images can be projected onto a screen, but virtual images cannot.


  True
• Give an example of a device that uses virtual images.

  Magnifying glass
• Geometric optics uses ray diagrams to model light behavior without considering wave-like properties.
• Wave optics models light using wave equations rather than ray diagrams.


  True
• Concave lenses diverge light to form virtual, upright images.
• Geometric optics deals with the behavior of light as it interacts with optical components like lenses and mirrors
• Convex lenses are thicker at the center than the edges, causing light rays to converge
• Match the lens type with its image formation:

  Convex Lens ↔️ Real, Inverted

  Concave Lens ↔️ Virtual, Upright