Question

(vi). the figure shows an object and its image formed on a screen by a thin lens.

by using appropriate rays complete the diagram to show the position of:
i) the lens.
ii) the two principal foci.

14.(a)(i) state the difference between transverse and longitudinal wave.
(ii) give one example of a transverse wave and one example of a longitudinal wave.

Explanation:

🆕 New Concept Discovered: Thin Lens Ray Diagrams
How light rays travel to form images

Step 1: Locate the Lens

To find the position of the thin lens:

1. Identify the straight ray that passes directly from the top of the object to the top of the inverted image without bending. This ray passes through the optical center of the lens.
2. The lens is positioned vertically at the intersection of this central ray and the principal axis (the horizontal line).
3. Draw a vertical line with arrows at both ends pointing outwards to represent a thin converging (convex) lens at this central vertical axis.

Step 2: Locate the Principal Foci

To find the two principal foci (\(F\)):

1. First Focus (on the right side): Draw a ray starting from the top of the object parallel to the principal axis. When it hits the vertical plane of the lens, it refracts and travels straight to the top of the image. The point where this refracted ray crosses the principal axis is the focal point on the right, labeled \(F\).
2. Second Focus (on the left side): Draw a ray from the top of the object that passes through the principal axis on the left side and hits the lens. After passing through the lens, this ray travels parallel to the principal axis to reach the top of the image. The point where this ray crosses the principal axis on the left is the second focal point, labeled \(F\).

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Answer:

1. The Lens: Positioned vertically at the central vertical axis where the straight ray from the top of the object to the top of the image intersects the horizontal principal axis.
2. The Two Principal Foci (\(F\)):

• The right focus is where the ray parallel to the principal axis from the object refracts through the lens and crosses the horizontal axis.
• The left focus is where a ray traveling from the top of the object passes through the horizontal axis before refracting parallel to the axis on the right side.