Overview: Lights & Its Basic Behaviors
📚 Topic Overview: LIGHT – Light & Its Basic Behaviours
This module covers the foundation concepts of Light for the AP TET exam—Light, Shadows,
Transparency Levels, Pinhole Camera, and Reflection using Mirrors. Each section uses
simple language, Telugu hints, real-life classroom-friendly examples, and exam-oriented
memory aids to help teachers and aspirants understand and teach effectively.
1. LIGHT – Meaning, Behaviour & Basic Ideas
Concept / Theory
Light is a form of energy that enables us to see objects. When light from a source reaches an object
and then reaches our eyes, the object becomes visible. At school level, we consider that light travels
in a straight line. Objects may emit their own light (luminous) or reflect light from another source
(non-luminous).
Analogy / Examples
- A torch in a dark room shows only what it points at—just like water flowing in a pipe, light also follows a single straight path.
- సూర్యుడు వెలుగు ఇస్తాడు, కానీ చంద్రుడు తన సొంత వెలుగు ఇవ్వడు (reflected light only).
Conversions / Formulas
- No numerical conversions needed at TET level.
- Key behaviour: Light travels in a straight line.
| English | Telugu |
|---|---|
| Light | కాంతి / వెలుగు |
| Luminous | కాంతి ఇచ్చే |
| Non-luminous | కాంతి ఇవ్వరాని |
| Ray | కిరణం |
| Beam | కాంతి పుంజం |
During a power cut, lighting a candle brightens only one direction because light moves in straight lines.
This helps students understand why shadows form easily.
Moon is non-luminous; it only reflects sunlight—common TET question trap.
2. Shadows – Formation & Behaviour
Concept / Theory
A shadow forms when an opaque object blocks light. It needs three things: a light source, an opaque object,
and a screen. Shadow shape depends on the shape and position of the object.
Analogy / Examples
- A child standing before a projector creates a dark outline on the board—same as shadow formation.
- ఉదయం నీడ పెద్దగా ఉంటుంది, మధ్యాహ్నం చిన్నగా ఉంటుంది—Sun position effect.
Conversions / Formulas
- No formula, but remember:
Shadow size depends on distance between object, source, and screen.
| English | Telugu |
|---|---|
| Shadow | నీడ |
| Opaque | అపారదర్శక |
| Screen | తెర |
| Light source | కాంతి మూలం |
| Umbra (basic idea) | పూర్ణ నీడ |
At morning assembly, children notice long shadows. Teachers can use this to explain the Sun’s angle
and shadow behaviour naturally.
If any one of the three conditions (light source, opaque object, screen) is missing—no shadow.
3. Transparent, Opaque & Translucent Objects
Concept / Theory
Objects are classified by how much light they allow to pass. This affects visibility and shadow clarity.
| Type | Light Passing | Example | Shadow |
|---|---|---|---|
| Transparent | Almost all light | Glass | Very faint |
| Translucent | Partial light | Oiled paper | Blurred |
| Opaque | No light | Wood, wall | Dark, clear |
Analogy / Examples
- Transparent = clean window; Translucent = curtain; Opaque = wall.
- పాలు కొంచెం పారదర్శకంగా ఉండవు—translucent example.
Conversions / Formulas
- Classification only—no formula.
| English | Telugu |
|---|---|
| Transparent | పారదర్శక |
| Translucent | అర్ధ పారదర్శక |
| Opaque | అపారదర్శక |
| Clarity | స్పష్టత |
| Shadow intensity | నీడ స్పష్టత |
Bathroom windows use frosted glass (translucent). Sunlight enters, but people cannot see clearly inside.
Dusty transparent glass becomes “translucent.” TET uses this as a trick MCQ.
4. Pin Hole Camera
Concept / Theory
A pinhole camera uses a very small hole to form an inverted, real image on a screen. It proves that light
travels in straight lines.
Analogy / Examples
- A tiny hole in a dark hut creates an inverted outdoor picture on the opposite wall.
- పిల్లలు రెండు డబ్బాలతో సులభంగా pinhole camera తయారు చేస్తారు—science project.
Conversions / Formulas
- No mathematical formula needed at TET level.
- Image is real, inverted, smaller or same size.
| English | Telugu |
|---|---|
| Pin hole camera | సూచి రంధ్ర కెమెరా |
| Inverted image | తలకిందుల బింబం |
| Real image | నిజ బింబం |
| Screen | తెర |
| Straight-line light | సూటి కాంతి మార్గం |
Holes in old wooden doors sometimes form an inverted picture of the street inside the dark room—natural pinhole camera.
If an MCQ asks “Nature of image in a pinhole camera?” answer:
Real + Inverted. (Size depends on distances)
5. Mirrors & Reflection
Concept / Theory
Reflection is the bouncing back of light from a surface like a mirror. Plane mirrors form virtual,
erect images of the same size. Reflection follows two rules: angle of incidence = angle of reflection,
and incident ray, reflected ray, and normal lie in the same plane.
Analogy / Examples
- Bouncing a ball on a floor is like light bouncing off a mirror.
- నీటి మీద మన ప్రతిబింబం కనిపించడం—natural reflection.
Conversions / Formulas
- Angle of incidence = Angle of reflection
- Plane mirror image: virtual, erect, same size, laterally inverted.
| English | Telugu |
|---|---|
| Reflection | ప్రతిఫలనం |
| Plane mirror | సమతల అద్దం |
| Virtual image | ఆభాస బింబం |
| Lateral inversion | పార్శ్వ మార్పు |
| Normal | లంబ రేఖ |
Ambulances have the word “AMBULANCE” written reversed so that it appears correctly in drivers’ rear-view mirrors.
If the image appears reversed left-right → it is lateral inversion, asked often in TET.