Introduction:
When light travels from one medium to another, it changes its direction. This phenomenon is known as refraction. The angle between the incident ray and the emergent ray is known as the angle of refraction.

Explanation:
When light travels from air to glass slab, it bends towards the normal because the speed of light is slower in glass than in air. The angle of refraction depends on the angle of incidence and the refractive index of the medium. The refractive index of glass is 1.5.

Formula:
The formula for the angle of refraction is given by Snell's law, which is:

n1sinθ1 = n2sinθ2

Where,
n1 = refractive index of the first medium (air)
n2 = refractive index of the second medium (glass)
θ1 = angle of incidence
θ2 = angle of refraction

Calculation:
Let us assume that the angle of incidence is 30 degrees.

n1sinθ1 = n2sinθ2
1sin30 = 1.5sinθ2
sinθ2 = 0.5
θ2 = sin^-1(0.5)
θ2 = 30 degrees

Therefore, the angle between the incident ray and the emergent ray when the light goes from air to glass slab is 30 degrees.

Conclusion:
In conclusion, the angle between the incident ray and the emergent ray depends on the angle of incidence and the refractive index of the medium. When light travels from air to glass slab, it bends towards the normal because the speed of light is slower in glass than in air. The angle of refraction can be calculated using Snell's law.