Assertion (A) : Higher the range, lower is the resistance of an ammeter.

Reason (R) : To increase the range of an ammeter additional shunt is added in series to it.

Assertion (A) : A step-up transformer cannot be used as a step-down transformer.

Reason (R) : A transformer works only in one direction.

Equipotentials at a large distance from a collection of charges whose total sum is not zero are -

Four charges $$-$$q, $$-$$q, +q and +q are placed at the corners of a square of side 2 L is shown in figure. The electric potential at point A midway between the two charges +q and +q is -