b
તીવ્રતા \(\,\,{\text{I}}\,\, = \,\,{\text{c}}\,\,{\varepsilon _0}{E_{r.m.s}}^2\,\, = \,\,\frac{P}{A}\,\,\,\therefore \,\,{E_{r.m.s}}^2\,\, - \,\,\frac{P}{{c{\varepsilon _0}\,\, \times \,\,4\pi {r^2}}}\,\,\therefore \,\,{E_0}\,\, = \,\,\left( {\frac{{2P}}{{c{\varepsilon _0}\,\, \times \,\,4\pi {r^2}}}} \right)\)

\( = \,\,{\left[ {\frac{{2\,\, \times \,\,1500}}{{3\,\, \times \,\,{{10}^8}\,\, \times \,\,8.85\,\, \times \,\,{{10}^{ - 12}}\,\, \times \,\,4\,\, \times \,\,3.14\,\, \times \,\,{{\left( 3 \right)}^2}}}} \right]^{\frac{1}{2}}}\,\, = \,\,100\,\,V\,\,{m^{ - 1}}\)