45. Drawing Ray Diagrams (Lenses)
1. Standard Symbols & Setup
Concave Lens Symbol: A vertical line with "V" shapes pointing outwards at the ends (representing the lens getting wider at the top and bottom).
Convex Lens Symbol: A vertical line with "V" shapes pointing inwards at the ends (representing the lens getting narrower at the ends).
The Axis: A horizontal line passing through the center of the lens.
Focal Points (F): Points on either side of the lens, equal distances from the center.
2F: Points exactly twice the distance of the focal length from the center.
2. Drawing for a Concave (Diverging) Lens
Ray 1: Draw a line from the top of the object parallel to the axis until it hits the lens.
Refraction: From the point where Ray 1 hits the lens, draw a dashed (virtual) line back to the focal point on the same side as the object. Then, draw a solid line continuing forward in that same direction.
Ray 2: Draw a solid line from the top of the object straight through the center of the lens. This ray is not refracted.
The Image: The image forms where the dashed line from Ray 1 and the solid line of Ray 2 cross.
Result: Concave images are always virtual, upright, and smaller (diminished).
3. Drawing for a Convex (Converging) Lens
Ray 1: Draw a line from the top of the object parallel to the axis until it hits the lens.
Refraction: Draw a solid line from the lens through the focal point on the opposite side.
Ray 2: Draw a solid line from the top of the object straight through the center of the lens.
The Image: The image forms where these two solid lines cross.
Variations for Convex Lenses:
The nature of the image depends on where the object is placed:
Object > 2F: Real, inverted, and smaller.
Object at 2F: Real, inverted, and the same size.
Object between F and 2F: Real, inverted, and larger.
Object < F (Inside focal point): The rays won't meet on the right. Trace them back with virtual lines. The image will be virtual, upright, and larger (this is how a magnifying glass works).