A solenoid of length 16 cm consists of closely spaced coils of wire wrapped tightly around a wooden core. The magnetic field strength is 2.5 mT inside the solenoid near its center when a certain current flows through the coils. If the coils of the solenoid are now pulled apart slightly, stretching it to 18 cm without appreciably changing the size of the coils, what does the magnetic field become near the center of the solenoid when the same current flows through the coils

B2 = 2.22mT

Explanation:

See attachment for the calculation.

Assuming the angle the magnetic field makes with the direction of current flow is the same in both cases and that the same current flows in both cases, then F1 = F2

See calculation below.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.

conservation of mass

mass before something happens = mass afterwards