Find the distance of the image from object O, formed by the combination of lenses in the figure :

In Millikan's oil drop experiment, what is viscous force acting on an uncharged drop of radius 2.0 $$\times$$ 10^$$-$$5 m and density 1.2 $$\times$$ 10³ kgm^$$-$$3 ? Take viscosity of liquid = 1.8 $$\times$$ 10^$$-$$5 Nsm^$$-$$2. (Neglect buoyancy due to air).

Electric field in a plane electromagnetic wave is given by E = 50 sin(500x $$-$$ 10 $$\times$$ 10¹⁰ t) V/m The velocity of electromagnetic wave in this medium is :

(Given C = speed of light in vacuum)

Five identical cells each of internal resistance 1$$\Omega$$ and emf 5V are connected in series and in parallel with an external resistance 'R'. For what value of 'R', current in series and parallel combination will remain the same?