15. A long straight wire of radius R carries a uniformly distributed current i. What is the magnetic field at a distance r<R from the center of the wire?(A)0(B)\( \frac{\mu_0 i}{2\pi r} \)(C)\( \frac{\mu_0 i}{2\pi R} \)(D)\( \frac{\mu_0 ir}{2\pi R^2} \)(E)\( \frac{\mu_0 iR}{2\pi r^2} \)

1. Four particles are moving on a plane under the same constant acceleration \( \vec{a} = \hat{y} \), each having its initial velocity vector as follows: (a)\( 10\hat{x}+10\hat{y} \), (b)\( 10\hat{x}+8\hat{y} \), (c)\( 8\hat{x}+10\hat{y} \), (d)\( 12\hat{x}+12\hat{y} \). If the respective displacements are \( R_a \), \( R_b \), \( R_c \), \( R_d \), which of the following is correct?(A)\( R_a ＞ R_b ＞ R_c ＞ R_d \)(B)\( R_c ＞ R_b ＞ R_d ＞ R_a \)(C)\( R_d ＞ R_a ＞ R_b ＞ R_c \)(D)\( R_d ＞ R_a ＞ R_c ＞ R_b \)(E)\( R_a ＞ R_c ＞ R_b ＞ R_d \)

15. A long straight wire of radius R carries a uniformly distributed current i. What is the magnetic field at a distance r<R from the center of the wire?
(A)0
(B)\( \frac{\mu_0 i}{2\pi r} \)
(C)\( \frac{\mu_0 i}{2\pi R} \)
(D)\( \frac{\mu_0 ir}{2\pi R^2} \)

(E)\( \frac{\mu_0 iR}{2\pi r^2} \)

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