Light, Shadows and Reflection: quick revision, 15 bites

Light Travels in Straight Lines

Light never bends on its own.

Light is a form of energy that travels in **straight lines** called rays. This single property explains shadows, eclipses, and why we cannot see around corners.

Takeaway. Straight-line travel of light is the foundation of every shadow and reflection you see.

Luminous vs Non-Luminous Objects

Some objects glow, others just borrow light.

Takeaway. Luminous objects are sources of light; non-luminous objects only reflect it.

Transparent, Translucent and Opaque

Three materials, three very different behaviours.

**Translucent** materials (butter paper, frosted glass, oiled paper) let some light pass, so you see a blurred image and a faint shadow.

Takeaway. Only opaque objects cast strong shadows; transparent and translucent objects let light through.

How a Shadow is Formed

Block the light, get a shadow.

Takeaway. A shadow is the dark region formed when an opaque object blocks straight-line light.

Shadow vs Image — Not the Same Thing

Shadow and image are not twins.

Takeaway. A shadow is just a dark outline; an image shows the object's actual colours and details.

Reflection: Light Bouncing Back

Light bounces — that's how mirrors work.

When light falls on a smooth, shiny surface like a mirror, it **bounces back** into the same medium. This is called **reflection**.

Takeaway. Reflection is the bouncing back of light from a shiny surface, and it follows a fixed angle rule.

The Law of Reflection

One equation rules every mirror.

Takeaway. The angle at which light hits a mirror equals the angle at which it bounces off.

Why Shadows Change Size

Move closer, shadow grows.

Takeaway. Shadow size is controlled by how far the object is from the light source.

Shadows Are Not Always Black

Not every shadow is pitch black.

Takeaway. Shadows have a dark umbra and a lighter penumbra — not one uniform black patch.

Eclipses: Shadows in the Sky

The sky's biggest shadow show.

Takeaway. Eclipses are natural proof that light travels in straight lines and opaque bodies cast shadows.

Pinhole Camera: Light in a Box

A tiny hole makes a real image.

A **pinhole camera** is a simple box with a tiny hole on one side. Light from an object passes through the hole and forms an **inverted (upside-down) image** on the opposite screen.

Takeaway. The pinhole camera proves light travels in straight lines by forming an inverted image.

Remember the Reflection Rule

In equals out — every time.

Think of a tennis ball bouncing off a wall: the angle it hits at is the angle it bounces back. **Angle in = Angle out** — that's the law of reflection.

Takeaway. Angle of incidence equals angle of reflection — just like a bouncing ball.

Exam Favourites from This Chapter

These questions always show up.

Takeaway. Practise the shadow-vs-image table and labelled reflection diagrams — they appear almost every year.

Your Eyes See by Reflected Light

You don't see objects — you see light.

You can see this page because light from a lamp or the Sun falls on it and **reflects into your eyes**. In a completely dark room, even a bright red apple is invisible — there is no light to reflect.

Takeaway. Vision happens when reflected light from an object enters your eyes.

Never Look at the Sun Directly

Bright light can damage your eyes.

Takeaway. Protect your eyes — observe the Sun only through safe indirect methods.