Microwave oven acts on the principle of :

To find the focal length of a convex mirror, a student records the following data :

Object Pin	Convex Lens	Convex Mirror	Image Pin
22.2 cm	32.2 cm	45.8 cm	71.2 cm

The focal length of the convex lens is f₁ and that of mirror is f₂. Then taking index correction to be negligibly small, f₁ and f₂ are close to :

Three capacitors each of 4 $$\mu $$F are to be connected in such a way that the effective capacitance is 6 $$\mu $$F. This can be done by connecting them :

A series LR circuit is connected to a voltage source with
V(t) = V₀ sin$$\Omega $$t. After very large time, current I(t) behaves as
(t₀ >> $${L \over R}$$) :