Question

Which of the following will never give a real image?

• A. convex lens
• B. concave lens
• C. concave mirror
• D. all of these

Answer 1

Answer:

B. concave lens

Properties of Concave Lenses and Image Formation

• A concave lens is also known as a diverging lens because it spreads out parallel light rays that pass through it.
• It is thinner in the middle and thicker at its edges, causing light to bend outwards.
• Regardless of the object's position relative to the concave lens, the image formed is always virtual, erect (upright), and diminished (smaller).
• The image is always located between the optical center and the principal focus (F1) on the same side of the lens as the object.

Understanding Real vs. Virtual Images

• A real image is formed when light rays actually converge and meet at a point after reflection or refraction.
• Real images can be projected onto a screen and are always inverted relative to the object.
• A virtual image is formed when light rays only appear to diverge from a point after reflection or refraction.
• Virtual images cannot be projected onto a screen and are always erect (upright) relative to the object.

Why a Concave Lens Never Forms a Real Image

• Due to its diverging nature, a concave lens causes parallel light rays to spread out after passing through it.
• These diverging rays never physically intersect to form a real image. Instead, they only appear to originate from a point behind the lens when extended backward, leading to a virtual image.

Competitive Exam Facts & Applications

• Contrast with Convex Lens: A convex lens (converging lens) can form both real and virtual images. It forms a real image when the object is placed beyond its principal focal point (F).
• Concave Mirror: Unlike a concave lens, a concave mirror (converging mirror) can form both real and virtual images depending on the object's position. It forms a real image when the object is placed beyond its focal point.
• Convex Mirror: Similar to a concave lens, a convex mirror (diverging mirror) always forms a virtual, erect, and diminished image.
• Applications of Concave Lenses:
  • Used to correct myopia (short-sightedness), a vision defect where distant objects appear blurred because light focuses in front of the retina.
  • Found in Galilean telescopes (as the eyepiece).
  • Used as beam expanders in laser systems to increase the diameter of the laser beam.
  • Used in peepholes of doors and some camera lenses.