# NCERT Physics Class 12 Exemplar Ch 4 Moving Charges and Magnetism Part 7

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Q.28 A multirange current meter can be constructed by using a galvanometer circuit as shown in Fig. We want a current meter that can measure , and using a galvanometer of resistance and that produces maximum deflection for current of . Find that have to be used

Solution:

For

For

And for

Gives

Q.29 Five long wires , each carrying current are arranged to form edges of a pentagonal prism as shown in Fig. Each carries current out of the plane of paper.

(a) What will be magnetic induction at a point on the axis? Axis is at a distance from each wire.

(b) What will be the field if current in one of the wires (say) is switched off?

(c) What if current in one of the wire (say) is reversed?

Solution:

Zero

Perpendicular to towards left.

Perpendicular to towards left.