Problem: Calculate the value of Flux density in an iron ring with mean length of 60cm uniformly wound with 250 turns of wire. A current of 2A flows through a wire and assume relative permeability 500 for iron.

Solution:
The flux density in the ring can be found using the formula:

B = μ*N*I / L

Where B is the flux density, μ is the relative permeability, N is the number of turns, I is the current and L is the mean length of the ring.

Given that:
- Mean length of the ring (L) = 60cm
- Number of turns (N) = 250
- Current (I) = 2A
- Relative permeability (μ) = 500

Substituting the values in the formula, we get:

B = 500 * 250 * 2 / 60
B = 20,833.33 A/m

Therefore, the flux density in the iron ring is 20,833.33 A/m.

Explanation:
The given problem can be solved using the formula for calculating flux density in a magnetic circuit. The formula relates the flux density to the number of turns, current, relative permeability and mean length of the ring. By substituting the given values in the formula, we get the required flux density in the iron ring.

It is important to note that the units of the variables in the formula should be consistent. In this case, the mean length is given in centimeters, so we need to convert it to meters before using it in the formula. Also, the units of flux density are in amperes per meter (A/m) which is the SI unit for magnetic field strength.

Assuming a relative permeability of 500 for iron is a reasonable assumption as it is a common value for iron. However, the actual value of relative permeability may vary depending on the type of iron and the magnetic field conditions.

Overall, this problem demonstrates the application of basic principles of magnetic circuits and provides an opportunity to practice using the formula for calculating flux density.