A moving coil galvanometer has resistance 50$$\Omega $$ and it indicates full deflection at 4mA current. A voltmeter is made using this galvanometer and a 5 k$$\Omega $$ resistance. The maximum voltage, that can be measured using this voltmeter, will be close to :

A wire of resistance R is bent to form a square ABCD as shown in the figure. The effective resistance between E and C is : (E is mid-point of arm CD)

In the figure shown, what is the current (in Ampere) drawn from the battery ?
You are given: R₁ = 15$$\Omega $$, R₂ = 10 $$\Omega $$, R₃ = 20 $$\Omega $$, R₄ = 5$$\Omega $$, R₅ = 25$$\Omega $$, R₆ = 30 $$\Omega $$, E = 15 V

A cell of internal resistance r drives current through an external resistance R. The power delivered by the cell to the external resistance will be maximum when :-