The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 $$\Omega $$ is

The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the celll will be

A cell having an emf $$\varepsilon $$ and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by

The power dissipated in the circuit shown in the figure is 30 watts. The value of R is