In the circuit shown, the current $${\rm I}$$ flowing through the $$50\,\Omega $$ resistor will be zero if the value of capacitor C (in $$\mu F$$) is ________ .

For the circuit shown in the figure, the Thevenin equivalent voltage (in Volts) across terminals a-b is _____.

In the circuit shown, the voltage V_x (in Volts) is ______.

The value of $$\sum\limits_{n = 0}^\infty n {\left( {{1 \over 2}} \right)^n}$$ is ________________.