Refractive Index: All You Need to Know – Mettler Toledo

Refractive Index: All You Need to Know

refractive index device
refraction phenomenon explained
Snell's Law: The Law of Refraction
Total Internal Reflection and the Critical Angle
Refractometer Principle Based on Snell's Law
Measuring Refractive Index
Influence of Temperature on Refractive Index Determination
Refractive Index Measurement Influences
Refractive Index Measurement
refractive index measurement guide
Improve Your Refractive Index Measurements

Glossary

  • Wavelength: The length of a single wave measured from one wave peak to the next.
  • Vacuum: An enclosed space from which matter and air has been partially removed.
  • Frequency: The number of waves produced each second. The unit of frequency is hertz (Hz).
  • Refractive index: An index that describes how fast a light beam travels through a particular medium in relation to the speed at which is passes through a second medium. The relationship is described by the formula n = c/v, where c is the speed of light in a vacuum and v is the phase velocity of light in the sample medium.
  • Angle of incidence: Angle between the normal and the incident ray.
  • Angle of reflection: The angle between the reflected ray / wave and an imaginary line drawn at 90 degrees to the reflecting surface.
  • Incident light: Light ray moving towards a surface or boundary.
  • Reflected light: Light ray leaving a surface or boundary.
  • Refraction: Process by which a wave changes speed and sometimes direction upon entering a more dense or less dense medium, e.g. a light ray changing direction when refracted by a lens.

Samples

Substance

Refractive Index

Vacuum

1.0000

Air

1.0002

Liquids at 20 °C, wave length of 589.3 nm

1-propanol

1.3848

2,4-Dichlorotoluene

1.5463

Acetone

1.3588

Aloe extract

1.334

Beer

1.346

Bromonaphtalene

1.6578

Butter

1.450

Coconut oil

1.440

Coffee

1.345

Cow milk

1.359

Dodecane

1.4218

Ethanol

1.3338

Glycerol

1.477

Honey

1.520

Ketchup

1.385

Natural rubber

1.540

Peanut oil

1.469

Plain youghurt

1.345

Propylene glycol

1.432

Sodium Chloride

1.334

Sodium hydroxide

1.333

Soy milk

1.350

Sulfuric acid

1.335

Sunflower oil

1.474

Virgin olive oil

1.469

Water (deionized)

1.333

Solids at room temperature

Diamond

2.417

Glass

1.517

 

What Does High Refractive Index Mean?

A high refractive index means that a light beam travelling through medium media moves slowly. In practice the more concentraded a binary substance is, the higher it's refractive index.
 

How Do Impurities Affect Refractive Index?

There are 2 scenarios of how impurities can affect refractive index:

  1. Considering liquid Impurities with a higher refractive index than your liquid sample: the velocity of light in the medium will decrease, and therefore increase the refractive index value.
  2. Considering liquid Impurities with a lower refractive index than your liquid sample: the velocity of light in the medium will increase, and therefore decrease the refractive index value.
     

How Do Solid Particles Affect Refractive Index?

If your liquid sample contains solid suspenses, it is recommended to pour the sample into the refractometer sample stage and wait for a fixed period of time (e.g. 10 sec), before starting the measurement.
 

Is It Possible to Measure the Refractive Index of Black or Colored Samples with a Refractometer?

Yes, black, dark and colored samples can be measured within seconds with a digital refractometer.
 

Why Can Refractive Index Measurement Be Used to Identify a Sample?

Refractive index can easily be used to identify a pure sample because each element has a unique refractive index. After a measurement, the index of refraction of the sample in question can be looked up to see what it corresponds to. In addition, when using an automatic refractometer refractive index can be automatically converted into other scales (e.g. Brix, %weight/weight, % volume/volume, and more).
 

Applications

Refractive Index Applications – Free PDFs

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