In which condition will the cast shadow of a form be very long?

When the light source is at a very low angle

The governing concept is the geometric relationship between light direction, object height, and cast-shadow length. When a light source is low, its rays travel across the ground at a shallow angle. The object then projects its height over a greater horizontal distance, producing a long shadow. In a simple model, shadow length is related to height divided by the tangent of the light’s elevation angle; as the elevation angle becomes smaller, the tangent decreases and the shadow becomes longer. Therefore, option A is correct. An overhead light produces a short shadow close to the object, so option B is incorrect. Transparency does not always determine a long shadow, and option C is too absolute. Option D is incorrect because a cast shadow is created precisely by the light-object-surface relationship.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Form.