# Light enters from air to glass having a refractive index of 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 x 108 m/s.

By BYJU'S Exam Prep

Updated on: September 25th, 2023

If light enters glass from the air with a refractive index 1.50, the speed of light is 2 x 108 m/s while the speed of light in a vacuum is 3 x 108 m/s. Steps to calculate the speed of light in a vacuum:

Step 1: It is given that

Speed of light in any medium = speed of light in a vacuum.

Speed of light in vacuum (c) = 3 x 108 m/s

Therefore, the speed of light in the air (c) is 3 x 108 m/s

Refractive index of glass (ng) = 1.5

Step 2: We can use the formula

Speed of light in a glass (v) = Speed of light in the air (c)/ Refractive index of glass (ng)

Step 3: Substituting the values

We know that,

Speed of light in a glass (v) = Speed of light in the air (c)/ Refractive index of glass (ng)

v = c/ng

v = 3 x 108/ 1.5

v = 2 x 108 m/s

### Speed of Light in Vacuum

Units of speed include:

• the SI derived unit; metres per second (symbol m s−1 or m/s),
• knots (nautical miles per hour, symbol kn or kt);
• kilometers per hour (symbol km/h);
• Mach number (dimensionless), speed divided by the speed of sound;
• miles per hour (symbol mi/h or mph);
• in natural units (dimensionless), speed is divided by the speed of light in a vacuum
• feet per second (symbol fps or ft/s);

Therefore, the speed of light in the glass is 2 x 108 m/s

Summary:

## Light enters from air to glass having a refractive index of 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 x 108 m/s.

Light enters from air to glass having a refractive index of 1.50. The speed of light in the glass is 2 x 108 m/s. The speed of light in a vacuum is 3 x 108 m/s. The refractive index of a medium is how the light travels via that medium.

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