A solenoid passing by a current of 5.0 A generates a magnetic field at its diameter of 50 μT. Thus the number of spirals per length scale is: A. 5.0 / π Spear / m

B. 10 / π Spear / m

C. 20 / π Spear / m

D. 25 / π Spear / m

D. 25 / π Spiral / m

Explanation:

Given;

current, I = 5 A

magnetic field strength, B = 50 μT = 50 x 10⁻⁶ T

The magnetic field strength is given as;

Therefore, the correct option is D. 25 / π Spiral / m

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form