Key relationship
n=sin[(A+δmin)/2]/sin(A/2); measured deviation=δ+zero offset.
Physics · Practical apparatus
Prism minimum-deviation reading
Sweep incidence and identify the lowest deviation before using the prism-index formula. An angular zero error shifts the readings. An arbitrary deviation substituted for the minimum overestimates the index.
Open the interactive experiment →Prism minimum-deviation reading
விலகலின் குறைந்த மதிப்பைத் தேடி பூஜ்யப் பிழையைத் திருத்திய பின்னரே ஒளிவிலகல் எண்ணைக் கணக்கிடவும்.
Key notes, relationships and model limits
Practical tip
Sweep incidence and identify the lowest deviation before using the prism-index formula. An angular zero error shifts the readings. An arbitrary deviation substituted for the minimum overestimates the index.
Common trap
A smooth curve minimum must be identified; a single incidence reading does not establish it.
Model limits
Ideal monochromatic prism; offset models vernier zero error. Index estimate is only justified at the actual minimum after correcting the zero.
What you will learn
Locate minimum deviation and account for angular zero error.
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
A60°,δmin37.18° gives n1.5.
Why this matters
The model connects prism minimum-deviation reading with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Which deviation should be used in the index formula?
- Any observed value
- Corrected minimum deviation
- Maximum deviation
Read the explanation
The formula assumes symmetric internal passage.
Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.