Question

An electromagnetic wave from a wire antenna travels (from the reader) toward the plane of the paper. At time t = 0.0 s it strikes the paper at normal incidence. At point O and t = 0.0 s, the magnetic field vector has its maximum value, 3.78×10-8 T, pointing in the negative y-direction. The frequency of this wave is 1.03×106 Hz.

What is the x-component of the associated electric field E at time t = 0.0 s? (Use the right-hand rule to determine the direction of E, and hence the sign of the x-component.)

The B-field and the E-field magnitudes are related via the speed of light. The directions of E, B, and the wave propagation direction are related by the right-hand rule.

Incorrect. Tries 1/12 Previous Tries

What is the magnitude of the Poynting vector of the wave at time t = 0.0 s?

Tries 0/12

What is the y component of the magnetic field at point O at time 4.85×10-7 s?

Answer 1

Let positive x axis be along East and positive y axis be along North. Then, positive z axis is outwards (out of the plane of paper).

The direction of the propagation of field is then in the negative z direction (this is the direction of the Poynting vector). The magnetic field is given to be in the negative y direction.

Since the direction of the Poynting vector can be determined from cross product of Electric and Magnetic field direction,

the Electric field must be in the positive x direction.

Magnitude of maximum Electric field value is: E_o = B_oc = 11.34 V/m

so,

ii] Choose O such that z = 0. Since the wave has a maximum value at t=0, use cosine function for expressing the magnetic field at O.

use t = 4.85 x 10^-7 s

so, the magnetic field is now pointing in the positive y direction at this time and its magnitude is +3.7799 x 10^-8 T.