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Light and Shadows - changing Shadows

Grade 3Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

The relationship between the distance of the object from the light source and the resulting shadow size can be observed in a dark room using a torch and a screen.

•

For the Sun's movement, let θ\theta represent the angle of the sun above the horizon. As θ\theta increases toward 90∘90^{\circ} (noon), the shadow length LL decreases.

📐Formulae

Object closer to light  ⟹  Larger shadow\text{Object closer to light} \implies \text{Larger shadow}

Object further from light  ⟹  Smaller shadow\text{Object further from light} \implies \text{Smaller shadow}

Low angle of light  ⟹  Long shadow\text{Low angle of light} \implies \text{Long shadow}

High angle of light  ⟹  Short shadow\text{High angle of light} \implies \text{Short shadow}

💡Examples

Problem 1:

A student measures the shadow of a stick at different times of the day. At 9:00 AM9:00\text{ AM}, the shadow is 120 cm120\text{ cm} long. At 12:00 PM12:00\text{ PM}, the shadow is 20 cm20\text{ cm} long. Why did the shadow get shorter?

Solution:

The shadow became shorter because the Sun moved higher in the sky.

Explanation:

At 9:00 AM9:00\text{ AM}, the Sun is at a lower angle. As it approaches 12:00 PM12:00\text{ PM}, it moves directly overhead. Light hitting an object from directly above creates a very small, short shadow compared to light hitting from a side angle.

Problem 2:

In a science experiment, a toy car is placed 10 cm10\text{ cm} away from a lamp. The shadow measured is 15 cm15\text{ cm}. If the car is moved to a distance of 30 cm30\text{ cm} from the lamp, will the new shadow be 'Greater than' (>>) or 'Less than' (<<) 15 cm15\text{ cm}?

Solution:

Less than 15 cm15\text{ cm} (<15 cm< 15\text{ cm}).

Explanation:

When the object moves further away from the light source (from 10 cm10\text{ cm} to 30 cm30\text{ cm}), it blocks a smaller area of the light beams, resulting in a smaller shadow.