Light: Shadows & Reflections | Science Grade 7 CBSE

Play with it

Why shadows grow and shrink

Slide the object between the lamp and the wall. As it moves closer to the lamp, its shadow gets bigger — because light spreads out in straight lines from the source.

Explore · Shadow sizedrag the slider

Object distance from lamp middle

The shadow is about the same height as the object.

Learn

The three big ideas

Light moves in perfectly straight lines (we draw these as rays). Luminous objects make their own light (the Sun, a lamp, a flame); non-luminous objects (a book, the Moon) are seen only by the light they reflect into our eyes.

How much light a material lets through sorts everything into three groups:

Transparent — light passes straight through (clear glass, still water). You can see clearly.
Translucent — only some light gets through (butter paper, frosted glass). Things look blurry.
Opaque — no light passes (wood, metal, you). These cast shadows.

A shadow forms when an opaque object blocks light from a source, leaving a dark region on a screen behind it. You always need all three: source + opaque object + screen.

Colour: a shadow is always dark — it is just "no light", so it does not take the object's colour.
Size & shape: change with the object's distance and the direction of the light (see the explorer at the top). Closer to the source ⇒ bigger shadow.
Eclipses are giant shadows: in a solar eclipse the Moon's shadow falls on Earth; in a lunar eclipse the Earth's shadow falls on the Moon.

Worked example. A lamp, a 6 cm tall toy, and a wall are in a line. The toy is halfway between the lamp and the wall. How tall is its shadow?

The wall is twice as far from the lamp as the toy is. Light rays spread in straight lines, so the shadow is magnified by that same factor:

shadow height = object height × (lamp→wall distance ÷ lamp→object distance) = 6 × (2 ÷ 1) = 12 cm.

Move the toy nearer the lamp and the ratio — and the shadow — grows even more.

Common mistake: thinking a red ball makes a red shadow. It doesn't — every shadow is dark, because a shadow is simply where light has been blocked.

Reflection is light bouncing off a surface. A smooth, shiny surface gives regular reflection (a clear image); a rough surface scatters light — diffuse reflection — so you see no image.

The image in a plane mirror is:

Virtual & erect (upright, can't be caught on a screen),
The same size as the object,
As far behind the mirror as the object is in front, and
Laterally inverted — left and right are swapped.

Lateral inversion is why AMBULANCE is painted back-to-front on the bonnet — it reads correctly in a driver's mirror.

Where you'll meet it

Straight-line light, all around you

Eclipses

A solar eclipse is the Moon's shadow sweeping across the Earth; a lunar eclipse is the Earth's shadow on the Moon. The same shadow rules you played with above — just on a cosmic scale.

Pinhole camera & the sun's image

Light through a tiny hole travels straight and crosses over, making an inverted image. Gaps between leaves do this too — the bright patches under a tree during an eclipse are tiny images of the Sun.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, the kind that test whether you can use the idea, not just recall it.

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Light: Shadows& Reflections