Assertion (A) : When radius of a current carrying loop is doubled, its magnetic moment becomes four times.

Reason (R) : The magnetic moment of a current carrying loop is directly proportional to the area of the loop.

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 -