A parallel beam of light is allowed to fall on a transparent spherical globe of diameter 30 cm and refractive index 1.5. The distance from the centre of the globe at which the beam of light can converge is _____________ mm.
A small bulb is placed at the bottom of a tank containing water to a depth of $$\sqrt7$$ m. The refractive index of water is $${4 \over 3}$$. The area of the surface of water through which light from the bulb can emerge out is x$$\pi$$ m2. The value of x is __________.
A light ray is incident, at an incident angle $$\theta$$1, on the system of tow plane mirrors M1 and M2 having an inclination angle 75$$^\circ$$ between them (as shown in figure). After reflecting from mirror M1 it gets reflected back by the mirror M2 with an angle of reflection 30$$^\circ$$. The total deviation of the ray will be _____________ degree.
A ray of light is incident at an angle of incidence 60$$^\circ$$ on the glass slab of refractive index $$\sqrt3$$. After refraction, the light ray emerges out from other parallel faces and lateral shift between incident ray and emergent ray is 4$$\sqrt3$$ cm. The thickness of the glass slab is __________ cm.