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Light, reflection and ray models - Science Year 7

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Introduction

Explain how light reaches your eyes, construct a plane-mirror reflection and trace an inverted pinhole-camera image. Separate a useful ray model from a photograph, and distinguish a mirror’s directional reflection from light scattered by a matte wall.

Use the supplied diagrams, coordinate models and fictional values. No laser, Sun viewing, bright-light eye test, cutting tools or camera construction is required. Year 7 is an editorial placement within England’s shared KS3 programme.

Trace light and construct plane-mirror reflection

A ray shows direction of light travel. In a uniform transparent medium, the elementary geometrical model treats light as travelling in straight lines. Put an arrow on every ray to show its direction. A line without an arrow can be ambiguous, and an eye does not send out a searching ray to illuminate an ordinary object. A ray is an ideal representation, not a literal narrow thread of material stretching between source and observer.

Light can travel through a vacuum; it is electromagnetic, unlike ordinary mechanical sound that needs a material medium. When light meets matter, some may be reflected, transmitted, absorbed or scattered. These possibilities can occur together. An opaque object transmits little of the relevant light, but it may still reflect enough toward an observer to be visible. Transparent does not mean perfectly nonreflecting.

Construct reflection from a plane mirror. Draw the surface and choose the reflection point. At that point draw a normal, a construction line at 90° to the surface. The normal is not a second physical mirror, and it is not necessarily vertical on the page: a tilted mirror has a correspondingly tilted normal. Draw the incoming ray toward the point and measure its incidence angle from the normal on the incident side.

The reflected ray leaves on the other side of the normal with an equal angle. Incident ray, reflected ray and normal lie in the same plane in this elementary construction. The convention measures both angles from the normal, not the mirror surface.

$θ_{i} = θ_{r}$

For an incidence angle of 20°, reflection is 20° from the normal and 70° from the surface. For 45°, the complementary angle also happens to be 45°; that special case can hide an incorrect measuring convention. If the incoming ray instead makes 55° with the surface, incidence is 90 − 55 = 35° and reflection is 35° from the normal. Always name the reference line with the number.

Supplied case	Incidence from normal/°	Reflection from normal/°	Reflection from surface/°
Measured from normal	20	20	70
Measured from normal	45	45	45
Incoming ray makes 55° with surface	35	35	55

Draw an original coordinate construction. On squared paper or a simple drawing tool, put a horizontal mirror on y = 0 and the normal on x = 0. Plot P at −2,2, O at 0,0 and Q at 2,2 in arbitrary equal-length units. Draw arrows P → O → Q. Equal horizontal/vertical changes give 45° to the normal on both sides. The table is a construction model, not measured beam positions or a requirement to shine light.

Point	x coordinate	y coordinate
P: point on incident path	−2	2
O: reflection point	0	0
Q: point on reflected path	2	2

A plane mirror’s image appears as far behind the mirror as the object is in front, is upright and has the same size in this ideal model. A point 30 cm in front corresponds to a virtual point 30 cm behind; object and image are 60 cm apart. The backward extensions of reflected rays locate the virtual image, but actual reflected light does not travel behind an opaque mirror to that point. A virtual image is not a claim that the observer is imagining things: it can be seen and photographed.

Explain seeing, specular and diffuse reflection

Seeing an ordinary object requires light reaching a receiver. A luminous source emits visible light. A nonluminous object such as a page is usually seen because light from a source is reflected/scattered from it into the eye. A complete explanation names both stages: source → object → eye. Without suitable illumination reaching the object, or without a pathway from it to the observer, the object may not be visible. Opening your eyes does not illuminate the object for you.

A white matte wall is visible from many directions because its surface sends reflected light over many directions. A smooth mirror gives specular reflection: a narrow incoming bundle is reflected into a correspondingly directional bundle. You only receive the rays that enter your eye. A mirror is therefore not automatically brighter from every viewing position, and a wall’s diffuse reflection does not mean light has been destroyed.

Local surface orientation matters. At small parts of an ideal rough surface, different local normals have different orientations. The local reflection rule can still apply, while originally parallel rays leave in a variety of directions. Diffuse scattering therefore does not contradict equal local incidence/reflection angles. Do not impose one large flat normal on every microscopic facet and then conclude the reflection law failed.

Compare two original paper models. In S, three parallel rays meet a flat surface with the same normal orientation; the reflected rays remain parallel in the ideal construction. In D, the same incoming directions meet three differently tilted small facets; each ray obeys its own local normal but the outputs point in different directions. Make a labelled sketch of each. The faceted drawing models roughness; it is not a magnified photograph or a claim that all rough surfaces consist of exactly three plane facets.

Reflection, absorption and transmission affect what reaches an observer. A coloured surface may absorb some wavelength ranges more strongly and reflect others, so its appearance depends on illumination as well as material. A red-looking object under white illumination is not necessarily bright red under every other lamp. This course does not require colour-filter experiments or a detailed microscopic theory of selective absorption.

Use the original SciShow Kids overview as a recap of light entering the eye and enabling sight. For the Year 7 work, extend that introduction with the ray constructions, local-normal reasoning and pinhole model in the written chapters. No bright-light or personal eyesight test is requested. Original: SciShow Kids, How Eyes Let Us See The World | SciShow Kids. The written explanations and native tasks work without sound or the external player.

Evaluate a ray explanation. A learner draws source → eye → page and claims that the eye illuminates the page. Reverse the incorrect final link and include source → page → eye. Another draws every reflected ray from a matte wall toward a single point; that would not model visibility from many directions. A third says diffuse reflection 'breaks the law'; draw different local normals to explain why equal local angles can still yield varied overall directions.

Ray diagrams are useful for direction, shadow boundaries and approximate image geometry when the scale is large enough relative to wavelength. They do not by themselves show intensity, colour spectrum, phase, interference, diffraction or every material interaction. A diagram with two rays represents selected paths, not proof that an object emits or reflects only two rays. Distinguish the model’s intended prediction from what it leaves out.

Model pinhole images and test the geometry

Trace paths through a small opening. A pinhole-camera model uses a small aperture in an otherwise opaque front and a screen behind it. Light from different object points travels in many directions. The opening selects a narrow set of paths reaching the screen; it is not a lens that bends and focuses those rays. In the ideal straight-ray construction, paths cross at the opening without bending there.

Light from the top of the object can continue downward through the hole to the lower part of the screen, while light from the bottom reaches higher. Left/right positions are also reversed relative to the object when comparing corresponding coordinates in the same orientation. An asymmetric symbol or two differently labelled points makes the inversion clearer than an unlabelled circle. The image is a real projection on the screen, unlike the backward-extension virtual image of a plane mirror.

Original coordinate model. Use centimetres for both axes. Put the pinhole at 0,0, the object plane at x = −40 and the screen at x = 10. The object has bottom at y = 0 and top at y = 20, so its height is 20 cm. Trace a straight ray from each point through the origin until it reaches the screen. The top ray reaches y = −5 and the bottom ray reaches y = 0. The 5 cm image is inverted relative to the object.

Object point	Object x/cm	Object y/cm	Screen x/cm	Screen y/cm
Object bottom	−40	0	10	0
Object top	−40	20	10	−5

The top ray’s slope is −1/2: at x = −40 it has y = 20, at the hole y = 0, and at x = 10 it has y = −5. This is a geometric check, not evidence that a real optical measurement has zero uncertainty. The bottom ray follows the axis y = 0. Draw arrows from object through hole toward screen; light does not start at the screen and run back to form the image.

Optional proportional extension. Similar triangles relate height magnitudes and perpendicular plane distances in this ideal aligned model. Object distance is measured from the object plane to the hole and screen distance from hole to screen. These are positive magnitudes, not the signed x coordinates.

$\frac{h_{i m a g e}}{h_{o b j e c t}} = \frac{d_{s c r e e n}}{d_{o b j e c t}}$

The first model gives 20 × 10/40 = 5 cm. Moving only the screen to 20 cm behind the hole gives a 10 cm image. Moving only the object to 80 cm away with the screen back at 10 cm gives 2.5 cm. Record which quantity changed; 'a longer camera always makes a better image' is unsupported. A larger projected image need not be brighter or sharper.

Supplied arrangement	Object height/cm	Object distance/cm	Screen distance/cm	Image height magnitude/cm
Original model	20	40	10	5
Screen farther from hole	20	40	20	10
Object farther from hole	20	80	10	2.5

A larger opening lets through more light but also admits a wider bundle from each object point, which can blur the image. A smaller opening can improve the geometrical selection while making the image dimmer; making it ever smaller does not improve sharpness forever because diffraction eventually matters. This lesson uses an ideal pinhole approximation, not a universal hole-size prescription, lens focus equation or build manual.

Produce evidence with clear limits. Submit the equal-angle construction, S/D surface sketches, source → object → eye chain and labelled pinhole coordinates. Explain virtual versus projected images and distinguish positive sizes from signed positions. Use supplied values or your own explicitly fictional model. A diagram/model portfolio is not proof of a physical light-box experiment, Sun observation, eyesight assessment or completed camera construction. Never look into the Sun or a laser to test the model.

Interactive Tasks

Quiz: Test Your Knowledge

What does a light ray represent in this course? (A direction of travel in an ideal geometrical model) (!A solid material thread connecting two objects) (!A searching beam emitted by every eye) (!A complete account of every wave effect)

How is the normal constructed at a plane mirror? (Perpendicular to the surface at the reflection point) (!Always horizontal regardless of the mirror orientation) (!Along the mirror surface) (!Along whichever ray looks brightest)

An incident ray is 20° from the normal. What is its reflection angle from the normal? (20°) (!70°) (!40°) (!90°)

An incoming ray is 55° from the surface. What is the reflection angle from the normal? (35°) (!55°) (!110°) (!145°)

What is a complete light path for seeing an ordinary illuminated page? (Source to page to eye) (!Eye to page with no source required) (!Page to source with no receiver) (!Eye to source to page as the necessary direction)

Why can a matte wall be visible from many positions? (Reflected light is distributed over many directions) (!The wall destroys every incident ray) (!The eye supplies all the wall’s light) (!Diffuse reflection requires one identical normal for every facet)

Why can diffuse reflection coexist with the local reflection rule? (Different parts have different local normals) (!All local reflection angles must differ from incidence) (!There are no local surfaces) (!The normal has to point toward the observer)

Where is the image of a point 30 cm in front of an ideal plane mirror? (30 cm behind the mirror as a virtual image) (!60 cm behind the mirror as a real screen projection) (!At the observer’s eye only) (!30 cm in front as a second physical object)

What happens to ideal rays at a pinhole in the supplied model? (They continue straight and cross without bending there) (!They bend as if the opening were a converging lens) (!They reverse direction and return to the object) (!They all merge permanently into one object point)

A 20 cm object is 40 cm from the hole and the screen is 10 cm behind it. What is the image-height magnitude? (5 cm) (!80 cm) (!50 cm) (!2 cm)

Memory Game

Normal	A line perpendicular to a surface at the point being considered
Incidence angle	Angle between incoming ray and local normal
Reflection angle	Angle between outgoing ray and local normal
Specular reflection	Directional reflection from a smooth surface in the model
Diffuse reflection	Reflected light distributed over varied directions
Virtual image	An image located by backward extensions without actual ray convergence there

Drag and Drop

Arrow on an incoming ray	Light travels toward the reflection point
Backward extension behind a plane mirror	A construction locating a virtual image
Different normals on a rough surface	Local equal angles can give varied outgoing directions
Top-point ray through a pinhole	Straight continuation can reach the lower screen
A larger pinhole opening	More admitted light with possible geometrical blur

Crossword Puzzle

NORMAL	What perpendicular construction line sets the angle reference?
MIRROR	What smooth reflective object can produce a virtual image?
REFLECTION	What process redirects light at a surface?
SPECULAR	What term describes directional mirror-like reflection?
DIFFUSE	What term describes reflected light spread over directions?
PINHOLE	What small aperture selects rays in the simple lensless camera?

LearningApps

Optional extra practice. Choose an appropriate activity with your teacher. If the external collection is unavailable, use the native activities and independent tasks in this course.

Cloze Text

Open Tasks

Easy

Trace a seeing pathway: Explain source, ordinary object and receiver; correct a diagram in which an eye illuminates a page.
Construct a normal: Draw a surface and perpendicular normal at one point, then rotate the surface and explain what happens to the normal.
Calculate reflection angles: Complete all three angle-table cases and explain why the 45° special case can hide a wrong reference convention.
Locate a mirror image: Place a virtual point for an object 30 cm in front of a mirror and distinguish its 30 cm image distance from the 60 cm object–image separation.

Standard

Draw the coordinate reflection: Plot P, O, Q and the surface/normal, add arrows and verify the equal 45° angles with a geometrical explanation.
Compare S and D surfaces: Sketch parallel incoming rays at a flat surface and three differently tilted facets; explain local normals and outgoing directions.
Trace the pinhole coordinates: Plot object top/bottom, hole and screen in the supplied centimetre model; trace directions and label inversion.
Calculate camera-image sizes: Use the optional proportional model for all three arrangements and explain which distance was changed.

Advanced

Distinguish image kinds: Explain why the mirror image is virtual while the pinhole image can be projected on a screen; identify real versus backward-extended paths.
Evaluate aperture claims: Explain the brightness/geometrical-blur trade-off and why making a hole indefinitely smaller does not guarantee endless improvement.
Critique ray-model predictions: Identify what ray diagrams can predict and what they omit about intensity, colour, interference, diffraction and actual material interaction.
Present an optics portfolio: Combine ray constructions, source/receiver reasoning, rough-surface sketches and pinhole calculations into a clear fictional model report with limitations.

Learning Check

Ray and observer reasoning: Explain how a source and ordinary object become visible.
Angle conventions: Solve the three reflection cases with the correct reference.
Virtual image and rough surfaces: Explain image location and diffuse reflection without changing the local law.
Pinhole paths: Use both coordinate rows to explain inversion.
Proportional image calculations: Find every supplied camera size and state assumptions.
Model evidence and limits: Evaluate aperture and ray-diagram claims.

Worked checks and assessment guidance

An ordinary nonluminous object is usually seen through source → object → eye, with light reflected/scattered toward the receiver. A ray arrow shows light direction, not a material thread or an illuminating search from the eye. Light can cross a vacuum and may be reflected, transmitted, absorbed or scattered when interacting with matter. Transparent material can still reflect some light; opaque does not mean nonreflecting.
The normal is perpendicular to the surface at the reflection point and turns with a tilted surface. Incidence/reflection angles are measured from it and are equal. At 20° incidence, reflection is 20° from normal and 70° from surface. At 45°, both references happen to give 45°. If incidence is given as 55° from surface, normal incidence is 90 − 55 = 35° and reflection 35° from normal. P at −2,2 → O at 0,0 → Q at 2,2 models equal 45° angles at a horizontal y = 0 mirror.
An ideal point 30 cm in front of a plane mirror appears 30 cm behind, so object–image separation is 60 cm. Backward extensions locate the virtual image; actual reflected rays do not converge behind the opaque mirror. On a rough surface, different local normal orientations can send parallel incoming rays into varied directions while preserving equal local angles. Diffuse reflection allows many viewing directions and does not mean light is destroyed.
With hole at 0,0, object plane x = −40 cm and screen x = 10 cm, a ray from the top at −40,20 continues through the origin with slope −1/2 to 10,−5. The bottom at −40,0 follows y = 0 to 10,0. Image height magnitude is 5 cm and the image is inverted. The paths cross without a lens-like bend at the hole. This is a real screen projection, unlike a plane mirror’s virtual image. The coordinates are fictional and ideal, not exact real measurements.
The positive magnitude ratio is image height/object height = screen distance/object distance for the aligned ideal pinhole geometry. Original 20 × 10/40 = 5 cm; doubling only screen distance to 20 cm gives 10 cm; doubling only object distance to 80 cm with screen 10 cm gives 2.5 cm. Signed screen coordinate −5 cm is not a negative height magnitude. The proportional extension does not guarantee real brightness, sharpness or a lens focus distance.
A wider aperture admits more light but also more paths from each object point, potentially increasing blur. A smaller opening makes a dimmer image and cannot improve sharpness without limit because diffraction eventually matters. Rays model directions and useful approximate geometry, not every wave effect, intensity or microscopic interaction. A diagram with two selected rays does not mean only two rays exist. The portfolio claims no laser/Sun/eyesight test or completed physical construction.

Learning evidence

Retain correctly arrowed reflection and viewing paths, normal/surface angle conversions, the P/O/Q construction, virtual-image distances, S/D local-normal sketches, labelled pinhole-coordinate rays and all proportional cases. Explain inversion, real versus virtual image and at least two model limits. No physical light-box, laser, Sun-viewing, eyesight or construction competence is asserted.

OER and Wikipedia

Original explanations, angle/coordinate tables, S/D sketch tasks, pinhole cases, activities and complete worked feedback. The Commons reflection reference remains unchanged with its actual source/creator/licence. An additional diffuse-reflection file was not available to the native renderer and is not included as a broken embed; the full concept is taught through local-normal reasoning and original S/D diagram tasks. The original SciShow Kids video was freshly checked for title, publisher, playability, embedding and preview; the preview was inspected but the whole film was not watched and no transcript/timestamp claim is made. It is a recap, not the sole Year7 teaching. No protected figure, build directions, source worksheet or extended quotation is reproduced.

Department for Education: KS3 Science, Light waves, with editorial Year7 allocation. OpenStax Physics: Reflection, consulted for angle/local-normal and virtual-image concepts; the normal is perpendicular to the local surface, not necessarily vertical on a page. Curved-mirror equations, laboratory laser procedures and source figures are not copied. Australian National University: Make a pinhole camera, consulted for the straight-path/inversion explanation and aperture trade-off; its cutting/build/outdoor directions are not part of this course. Diffraction qualifies the too-small-aperture limit. Reviewed 13 November 2026.

Reflection angles.svg, No machine-readable author provided. Arvelius assumed (based on copyright claims)., CC BY-SA 3.0. Unchanged original; caption and learning activities are original.