Final answer:
When parallel rays from a faraway source strike a diverging lens at a 10-degree angle, the image appears to be on the focal plane above the optical axis, at a height determined by the tangent of the angle and the focal length of the lens.
Step-by-step explanation:
For parallel rays striking a diverging lens with a given focal length, the rays diverge after passing through the lens. However, by tracing the rays backward on the side the rays come from, they appear to come from a common point, which is the virtual focal point of the lens.
For rays entering at an angle to the optical axis, such as at 10 degrees in your question, the image does not form at the focal point itself.
Instead, it will appear on the focal plane, which is a plane perpendicular to the optical axis and passes through the focal point. Since the rays are 10 degrees from horizontal, the vertical position can be determined by the tangent of the angle multiplied by the focal length of the lens.
In your case with a 20 cm focal length diverging lens and rays at an angle of 10 degrees, the image seems to come from a point on the focal plane located at a height of:
Tan(Θ) × focal length
= Tan(10°) × 20 cm
Approximately 3.5 cm above the optical axis (assuming the ray is coming from above the optical axis).
This is the vertical position of the image that is viewed as upright and smaller in height compared to the source. Note that since the source is far away (infinitely distant), the rays are considered parallel, and hence the calculations assume parallel rays.