Key relationship
sin i = n sin r; lateral shift = t sin(i−r)/cos r.
Physics · Class 12
Glass slab refraction
Ray Optics & Optical Instruments
The ray bends toward the normal on entering glass and away on leaving. The parallel faces restore its original direction but shift its line sideways. Thickness changes shift while leaving the refraction angle fixed.
Open the interactive experiment →Glass slab refraction
கண்ணாடிக்குள் நுழையும்போது கதிர் செங்குத்தை நோக்கி வளையும். இணையான முகங்களால் வெளியேறும் கதிர் இணையாகப் பக்கவாட்டில் நகரும்.
Key notes, relationships and model limits
Remember
The ray bends toward the normal on entering glass and away on leaving. The parallel faces restore its original direction but shift its line sideways. Thickness changes shift while leaving the refraction angle fixed.
Common trap
A parallel slab does not generally change the final ray direction.
Model limits
Parallel slab in air; homogeneous refractive index; no absorption. The emergent direction equals the incident direction.
What you will learn
Apply Snell’s law and distinguish bending from lateral shift.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
For n=1.5 and i=45°, r≈28.13°; a 4 cm slab shifts about1.32 cm.
Why this matters
The model connects glass slab refraction with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
At normal incidence the slab lateral shift is?
- The thickness
- Zero
- Twice the thickness
Read the explanation
At i=r=0, sin(i−r)=0.
Course connection: Class XII Chapter 9. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.