# Does a light pulse get amplified when it goes to a less dense medium?

1. Jan 16, 2010

### quantum123

Since a string pulse get amplified when it enters a less dense medium such as from the thick heavy rope to a lighter string, why does not light do the same?

2. Jan 16, 2010

### jety

3. Jan 16, 2010

### quantum123

Come to think of it, there is a medium and the medium is the electromagnetic field.

4. Jan 16, 2010

### jety

It never goes to a "different medium".

5. Jan 16, 2010

### Bob S

When light goes from a medium such as glass (index of refraction n=1.5) to air, about 4% of the energy is reflected, and 96% of the energy is transmitted. The ratio of the transverse E (electric) vector to the transverse H (magnetic) vector in light is proportional to 1/n, so the ratio E/H increases when the light goes from glass to air. But the transmitted energy decreases by 4%. So the amplitude E increases, but the transmitted energy, which is proportional to E times H (Poynting vector), decreases.
Bob S

6. Jan 16, 2010

Thanks, Bob!