Two wires of same length are shaped into a square and a circle. If they carry same current, ratio of the magnetic moment is (a) \(2: \pi\) (b) \(\pi: 2\) (c) \(\pi: 4\) (d) \(4: \pi\)

Short Answer

Expert verified
The ratio of the magnetic moment of the square to the circle is \(\pi: 2\), which corresponds to option (b).

Step by step solution

01

Calculate the magnetic moment of the square wire

Let's denote the length of the wire as L. Since the wire is shaped into a square, each side of the square will have a length of L/4. The area A_s of the square can be calculated as: \[A_s = (\frac{L}{4})^2\] Now, let's denote the current passing through the wire as I. The magnetic moment M_s of the square can be calculated as: \[M_s = I \cdot A_s\] By substituting the area of the square, we get: \[M_s = I \cdot (\frac{L}{4})^2\]
02

Calculate the magnetic moment of the circle wire

To find the magnetic moment of the circle wire, we first need to determine its radius. Since the circumference of the circle is equal to the length of the wire, we have: \[2\pi r = L\] Solving for the radius r, we get: \[r = \frac{L}{2\pi}\] Now, we can calculate the area A_c of the circle as: \[A_c = \pi r^2\] Substituting the radius, we get: \[A_c = \pi (\frac{L}{2\pi})^2\] The magnetic moment M_c of the circle can be calculated as: \[M_c = I \cdot A_c\] By substituting the area of the circle, we get: \[M_c = I \cdot \pi (\frac{L}{2\pi})^2\]
03

Calculate the ratio of the magnetic moments

We need to find the ratio of the magnetic moments of the square and the circle: \[\frac{M_s}{M_c} = \frac{I \cdot (\frac{L}{4})^2}{I \cdot \pi (\frac{L}{2\pi})^2}\] We can see that the current I and the length L will cancel out, so the ratio of the magnetic moments simplifies to: \[\frac{M_s}{M_c} = \frac{(\frac{1}{4})^2}{\pi (\frac{1}{2\pi})^2}\] After calculating the ratio, we arrive at the following: \[\frac{M_s}{M_c} = \frac{1}{16} \cdot \frac{4\pi^2}{\pi}\] This further simplifies to: \[\frac{M_s}{M_c} = \frac{\pi}{2}\] So the ratio of the magnetic moment of the square to the circle is \(\pi: 2\), which corresponds to option (b).

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