Need help in solving this.
The fixed outer legs of a lens measure calibrated for spectacle crown glass, n=1.523, are separated by 18mm when the instrument is new, but in wear, become separated by 20mm. What readings will this instrument give when placed upon a spectacle crown glass surface of power +5.00D?
The instrument will give correct readings when placed on glass of a certain refractive index. Find this index.
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