Question

PO
29. A wire of resistance 422 is used to wind a coil of radius 7 cm. The wire has a diameter of 1.4 mm and
the specific resistance of its material is 2 x 10-Qm. The number of turns in the coil
(A) 70
(B) 50
(C) 30
(D) 20
(A)
(B)
Ο Ο Ο
(C)
(D)​

Answer 1

Answer:

Correct option is

A

70

Explanation:

Correct option is

70

Let n be the number of turns in the coil, Then total length of wire used,

l=2πr×n=2π×7×10−2×n

Total resistance, R=ρAl

or 4=π(0.7×10−3)22×10−7×2π×7×10−2×n

∴n=70.