• summary_type: application
• word_count: 170

EM waves carry energy with density u = epsilon_0E^2 = B^2/mu_0 (electric and magnetic contributions are always equal). The Poynting vector S = (1/mu_0)(E x B) gives instantaneous energy flow per unit area. Average intensity: I = (1/2)cepsilon_0E_0^2 = E_0B_0/(2mu_0). For a point source of power P: I = P/(4pir^2). EM waves carry momentum: p = U/c (absorbed) or 2U/c (reflected). Radiation pressure: P_rad = I/c (absorbing surface) or 2I/c (reflecting surface). Force = P_radA. Numerical scale: sunlight intensity ~1400 W/m^2 gives radiation pressure ~5 x 10^-6 Pa on an absorbing surface — negligible on Earth but significant in space (solar sails) and stellar interiors. JEE calculations: (1) Given E_0 or B_0, find intensity using I = (1/2)cepsilon_0*E_0^2. (2) Given power and area, find E_0. (3) Pressure and force from intensity.