To convert a galvanometer into a voltmeter one should connect a

A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is

The magnetic flux through a circuit of resistance R changes by an amount $$\Delta $$$$\phi $$ in a time $$\Delta $$t. Then the total quantity of electric charge Q that passes any point in the circuit during the time $$\Delta $$t is represented by

A telescope has an objective lens of 10 cm diameter and is situated at a distance of one kilometer from two objects. The minimum distance between these two objects, which can be resolved by the telescope, when the mean wavelength of light is 5000 $$\mathop A\limits^ \circ $$, is of the order of