Light & Reflection

Start from the one fact everything else hangs on: in a uniform medium light travels in a straight line (rectilinear propagation). That straight-line travel is why opaque objects cast sharp shadows and why a pinhole camera makes an inverted image. When light hits a surface it bounces off — reflection — and it obeys the law of reflection: the angle of incidence equals the angle of reflection (i = r), both measured from the normal (the line perpendicular to the surface). A smooth shiny surface gives regular reflection (a clear image); a rough surface gives diffused/irregular reflection (the rays scatter), which is how we see most non-shiny objects — and a key point CTET likes: diffused reflection does NOT mean the law is broken, it still holds at every tiny point. A plane mirror forms an image that is virtual (cannot be caught on a screen), erect, the same size as the object, and as far behind the mirror as the object is in front, but laterally inverted — left and right are swapped (hence AMBULANCE written reversed on the front of the vehicle, and why your right hand looks like the mirror's left). Real images can be projected on a screen (formed by converging rays, e.g. on a cinema screen); virtual images cannot. Pedagogy: the classic child misconception is that 'we see objects because our eyes send out rays' (the old extramission idea) — children should learn we see because light from a source reflects off the object into the eye. Another is that a mirror 'flips top-to-bottom' — it does not; it reverses front-to-back, which we perceive as left-right (lateral) inversion. How it is tested: a stem describes a child writing on a card held to a mirror, or asks which property of a plane-mirror image is wrong, or gives a ray hitting a mirror at a stated angle and asks the angle of reflection. Fix the misconceptions with a torch-and-mirror activity and mirror-writing on graph paper.

✅ Solved examples

✏️ Practice — try these, take hints as needed

📝 Topic test — 8 questions

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