Physics – 3.2.3 Thin lenses | e-Consult

Diagram: A ray diagram should be drawn showing two rays originating from the top of the object. One ray should be parallel to the principal axis and refract through the focal point to the other side. The other ray should pass through the focal point. The point where these two refracted rays intersect is where the image is formed. The image should be shown on the same side of the lens as the object, and it should be upright and smaller than the object.

Labels: The diagram must include labels for:

• Object (o): Represented by a small shape.
• Principal Axis: A horizontal line passing through the optical centre.
• Focal Length (f): Marked with dashed lines extending from the focal point.
• Focal Point (F): The point where parallel rays converge.
• Image (i): Represented by a small shape.
• Object Distance (u): The distance between the object and the lens (20 cm).
• Image Distance (v): The distance between the image and the lens. This should be calculated using the lens formula.

Lens Formula: The lens formula is 1/f = 1/u + 1/v. Substituting the values f = 15 cm and u = 20 cm, we get:

1/15 = 1/20 + 1/v

1/v = 1/15 - 1/20 = (4 - 3)/60 = 1/60

Therefore, v = 60 cm. The image is formed 60 cm from the lens on the opposite side of the object.