The minimum (shortest) wavelength is determined by the maximum energy of incident electrons, which depends on the accelerating voltage.

Atomic spectra typically consist of discrete lines corresponding to electronic transitions in atoms.

Maximum photon frequency ν = eV/h; for 42,000 V this yields about 1×10^19 Hz.

Exposure to high or prolonged doses of X-rays can damage DNA and increase the risk of cancer.

Isaac Newton proposed the corpuscular (particle) theory of light, so Newton is the correct answer.

10^-4 cm equals 1 μm, which lies in the infrared region of the spectrum.

The OCR answer key marks option A; the stopping potential increases with photon energy (inversely with wavelength) and the key indicates ≈1.85 V.

Human body at ~37°C emits thermal radiation in the infrared region of the electromagnetic spectrum.

X-rays are produced when high-energy electrons strike heavy metal targets, producing both continuous and characteristic radiation.

Objects opaque to visible light may appear invisible to the eye when viewed under X-rays since X-rays pass differently through materials.