NESA Physics Electromagnetic Spectrum

Incorrect. A stationary electron produces a static electric field but no magnetic field, meaning it cannot generate an electromagnetic wave.

Incorrect. According to quantum mechanics, an electron in a stable atomic orbit does not emit radiation; if it did, it would continuously lose energy and spiral into the nucleus.

Incorrect. An electron moving at a constant velocity has zero acceleration, and electromagnetic waves are only produced by accelerating charges.

Correct. An electron moving in a circular path is constantly changing direction, meaning it experiences centripetal acceleration. According to classical electromagnetism, any accelerating charge emits electromagnetic waves.

Incorrect. The explanation of atomic emission spectra was developed later by Niels Bohr and other quantum physicists using quantum mechanics, not by Maxwell.

Correct. Maxwell formulated a set of equations that predicted the existence of electromagnetic waves traveling at the speed of light ($c$), establishing that light itself is an electromagnetic wave.

Incorrect. Maxwell's work firmly established the wave model of light; experimental support for the particle model came later from Einstein's explanation of the photoelectric effect.

Incorrect. Maxwell provided the theoretical framework for electromagnetic waves, but experimental confirmation of invisible light like infrared and radio waves was achieved by scientists like Herschel and Hertz.

This describes gamma rays specifically, which are just one type of high-energy electromagnetic radiation, rather than the general definition for all electromagnetic radiation.

This defines ionizing radiation, which includes high-energy particles (like alpha and beta particles) in addition to waves, and excludes non-ionizing electromagnetic radiation like radio waves and visible light.

While this correctly describes the mechanism of generation and the geometry of an electromagnetic wave, Option D provides the more complete and formal definition of the radiant energy itself and its propagation characteristics.

This is the comprehensive definition of electromagnetic radiation, characterizing it as radiant energy composed of synchronized oscillating electric and magnetic fields that propagate at the speed of light ($c$) in a vacuum.

The electric and magnetic fields in an electromagnetic wave are always perpendicular ($90^\circ$) to each other and to the direction of wave propagation.

Since the electric and magnetic fields are coupled components of the same wave, they always share the same wavelength and frequency.

The electric and magnetic fields oscillate in phase, meaning they reach their maximum amplitudes and zero crossings at the exact same time and position.

This description is inaccurate; because the fields are in phase, they cross the axis of propagation at the same time (the nodes), not at the peaks of their amplitudes.