When light enters normally into turpentine oil from water, its speed ___.
When light enters normally into turpentine oil (μ=1.47)from water, its speed ________ .
When a ray of light travelling in glass enters into water obliquely : (a) it is refracted towards the normal (b) it is not refracted at all (c) it goes along the normal (d) it is refracted away from the normal