Exams › JEE Advanced › Physics

An infinitely long straight wire lying along the x-axis (in the xy-plane) carries a current i = i0*t/T directed along +x, where i0 and T are positive constants and t is time. Consider a field point on the +y-axis at the origin's neighbourhood (just off the wire, on the +y side). Which statement is correct?

1. The displacement current near the point is in the +y direction.
2. The induced electric field at the point is in the -x direction.
3. The Poynting vector (E x B)/mu0 points toward the wire (in the -y direction).
4. The magnetic field at the point is in the +z direction.

Correct answer: The Poynting vector (E x B)/mu0 points toward the wire (in the -y direction).

Solution

B from a wire along +x, at a point on the +y side, is along -z (right-hand rule). The increasing current produces an induced electric field that opposes the increase, i.e. antiparallel to the current, so E is along -x. Then S = (E x B)/mu0 = ((-x) x (-z))/mu0-direction = (x x z)/mu0-direction = -y (since x x z = -y). So the Poynting vector points in -y, toward the wire, consistent with magnetic energy flowing into the growing field region.

Related JEE Advanced Physics questions

• What is the final velocity attained by the loop?
• A long coaxial cable is made up of two cylindrical conductors with radii a and b. The inner conductor carries a constant current i, while the outer conductor acts as the return path for the current. What is the self-inductance of a segment of the cable of length l?
• Determine the inductance per unit length for a loop created by connecting the ends of two infinitely long parallel wires, each with radius r, and separated by a distance d between their centers. Ignore the magnetic flux inside the wires and the effects at the ends.
• If the electromotive force is 10 V and the rate of change of current is calculated as 2.5 A/s, what is the self-inductance of the coil, given by L = e / (dl/dt)?
• The magnitude of the induced electric field in the orbit at any instant of time during the time interval of the magnetic field change is
• A semicircular loop of radius r is positioned on the axis of a large current-carrying circular ring of radius R (with R >> r). The loop is placed at an axial distance of R*sqrt(3) from the center of the ring, and the plane of the semicircular loop makes an angle of 53 deg with the plane of the ring. Find the mutual inductance M between the two coils.

⚔️ Practice JEE Advanced Physics free + battle 1v1 →