Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A lens is a piece of transparent material (like glass) bounded by two surfaces, at least one of which is a curved surface.
Convex Lens (Converging Lens): It is thicker in the middle than at the edges. It converges (brings together) parallel rays of light at a point called the Principal Focus ().
Concave Lens (Diverging Lens): It is thinner in the middle than at the edges. It diverges (spreads out) parallel rays of light, making them appear to come from the Principal Focus ().
Optical Centre (): The geometric centre of the lens. Light rays passing through do not deviate from their path.
Principal Axis: An imaginary horizontal line passing through the optical centre and the centers of curvature of the lens surfaces.
Focal Length (): The distance between the optical centre () and the principal focus () of the lens.
A convex lens can form both real (inverted) and virtual (erect) images depending on the position of the object.
A concave lens always forms a virtual, erect, and diminished (smaller) image, regardless of the object's distance.
📐Formulae
💡Examples
Problem 1:
If the radius of curvature () of a spherical lens is , calculate its focal length ().
Solution:
Explanation:
The focal length of a lens is half of its radius of curvature. Using the formula , we divide by to get .
Problem 2:
Calculate the magnification () if the height of the object () is and the height of the image () formed by a lens is .
Solution:
Explanation:
Magnification is the ratio of the height of the image to the height of the object. Since and , the magnification is , meaning the image is twice as large as the object.
Problem 3:
Find the difference in focal lengths of two lenses, Lens A and Lens B, where Lens A has a focal length of and Lens B has a focal length of .
Solution:
Explanation:
Subtracting the focal length of Lens B from Lens A gives a difference of .