The primary source of X-ray photons from an X-ray tube is characteristic radiation.

A thin radiolucent line which follows the root outline on X-rays is the periodontal ligament.

Which of the following is useful for studying the movements of the tongue: Fluoroscopy.

The wavelength of X-ray photon depends upon kilo voltage.

The wavelength of X-rays is inversely proportional to their energy, and the energy of X-ray photons is determined by the kilo voltage (kV) used in the X-ray tube. Higher kV results in higher energy and shorter wavelength photons, which are more penetrating and are used for imaging denser tissues, while lower kV results in lower energy and longer wavelength photons, which are less penetrating and are used for imaging softer tissues. The other factors mentioned (milli amperage, distance between source and object, and quantity of electrons in the cathodic stream) affect the intensity of the X-ray beam but not the wavelength of the photons.

In cephalometric radiography, the distance between the subject and the source of X-ray is 5 feet.