In the crown glass code 523-589, what does the second part (589) indicate?

• A. Abbe value 58.9
• B. Refractive index 1.589
• C. Abbe value 52.3
• D. Refractive index 1.523

Answer: (A)

The second part shows the material’s dispersion, expressed as the Abbe value. In crown glass code 523-589, 589 points to an Abbe number of about 58.9. The Abbe number measures how much the glass spreads different wavelengths (chromatic dispersion); a higher value means less dispersion and less chromatic aberration in lenses. The first part of the code relates to the refractive index (about 1.523), while the second part specifically conveys how the glass handles dispersion rather than speed of light alone.