Optics & Waves · GCSE Physics Topic 6
Plane Mirror Reflection & Periscope Simulator
Key exam takeaway: Walking closer to a plane mirror does NOT make the image larger! The physical image remains equal in size; only the visual perspective angle increases.
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Parameter Controls
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Live Derivations & Metrics
Image Distance s'
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Image Height H'
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Min Full View Mirror Length
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Image Symmetry & Nature
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: A 1.6m person stands 2m before a plane mirror. What is image height, distance between person and image, and effect of stepping 1m back?
Step-by-Step Derivation:
- Image height is 1.6m. Distance to image is 2+2=4m. Stepping 1m back leaves image height strictly unchanged at 1.6m.
Worked Problem
Problem: Why use a transparent glass plate instead of an opaque mirror in plane mirror experiments? Why identical candles?
Step-by-Step Derivation:
- Glass allows seeing reflection while viewing through to locate image position. Identical candles test size equality via equivalent substitution.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: If the glass plate is tilted instead of vertical, what happens to the second candle?
Answer Key: The second candle cannot align with the image on the tabletop because tilting raises or depresses the image plane.
Q2. Variant 2: A clock reflected in a plane mirror shows 9:25. What is the actual time?
Answer Key: Plane mirror reflection reverses left-right. Symmetrical time calculation: 12:00 - 9:25 = 2:35.
Q3. Variant 3: Walking with your back to the moon after rain, is the brighter puddle or dry ground?
Answer Key: Both follow reflection laws. With back to moon, water reflects light away (looks dark); rough ground scatters light back into eyes (looks bright).
Frequently Asked Questions & Misconceptions
Why can't a plane mirror virtual image be captured on a screen?
Virtual images are cognitive extrapolations of diverging reflected rays; no real photons focus behind the mirror.
Why do car side mirrors use convex mirrors instead of plane mirrors?
Convex mirrors diminish image size but substantially expand the field of view, minimizing blind spots.
In a corner reflector with two 90° perpendicular mirrors, is your image flipped or normal?
It shows your true unflipped perspective! Two successive reflections flip left-right twice, preserving true handedness.
Why does full-body viewing require at least half your height regardless of distance?
Reflected sightlines to head and feet form similar triangles with the mirror; the required aperture is a midline exactly 1/2 your height.