64. Optical density of 1 means:
Optical density (OD) of 1 means 90% absorbance, so only 10% of incident light transmits through the sample.
Option Analysis
A. 1% of the incident light is absorbed
Incorrect. OD=1 means log10(1/T)=1, so T=0.1 (90% absorbed), not 1%.
B. 10% of the incident light is transmitted
Incorrect. OD=1 = -log10(T), so T=10-1=0.1=10% transmitted. But option D correctly states the standard definition.
C. 10% of the incident light is absorbed
Incorrect. OD=1 means 90% absorbed (T=10%).
D. 90% of the incident light is transmitted (Correct)
OD = log10(I0/I) = 1 → I/I0 = 10-1 = 0.1 → 10% transmitted = 90% absorbed. Standard spectrophotometry definition.
Optical density of 1 means 90% of incident light transmitted
Optical density of 1 means 90% of incident light transmitted through sample—essential Beer-Lambert law concept for GATE Life Sciences biochemistry and microbiology.
OD Calculation
OD = log10(I0/I) = 1
I/I0 = 10-1 = 0.1 = 10% transmitted
90% absorbed by chromophores/cells
Transmittance Table
| OD | % Transmitted | % Absorbed |
|---|---|---|
| 0 | 100% | 0% |
| 1 | 10% | 90% |
| 2 | 1% | 99% |
GATE Applications
- OD600 measures bacterial growth (0.1-1.0 range)
- Protein assays (Bradford, BCA) use OD280/OD562
- Enzyme kinetics track substrate depletion via absorbance changes
1 Comment
Kanica Sunwalka
June 26, 2026OD = 1 means 90 % absorbed and 10 % transmitted