Physics ISU


(a) Cathode Rays are invisible particles that are emitted from the cathode (negative end) and travel to the anode (positive end). These rays are called cathode rays because they originated from the cathode. They travel in a straight lines, possess kinetic energy (which means that they mush have some mass) they are high speed, negatively charged electrons.
(b) An "Electron Gun" is something that 'boils' out electrons at a high temperature from the cathode and they are accelerated towards the anode. The intensity of the electrons can be controlled. There is an electron lens, which focuses the highly accelerated electrons into a small spot. A deflation system can be used to move the focused spot across the phosphorescent screen.
(c) Electron guns are used in following way in a color television set. Electrons that are emitted out of the cathode travel at very high speeds towards the anode. Many of these electrons pass through an opening in the anode to form an electron beam. The electron beam passes between two sets of deflection plates before it hits the phosphorescent screen. By applying voltage, to the deflection plates, the electron beam can sweep up and down and side to side. A color television set uses three separate electron guns. Different phosphorescent compounds are applied that emit three different colors.

2(a) X-rays are short wavelength electromagnetic radiations. Cathode rays can produce x-rays when they strike an object. X-rays can cause some materials to glow. X-rays have a shorter wavelength than light, have a higher frequency than light and travel in waves. They are streams of high energy protons.

(b) How X-rays differ from :
(i)Cathode rays are high speed electrons, they travel in straight lines and X-rays travel in waves. Cathode rays are negatively charged particles, they have mass and can penetrate opaque objects.
(ii)Light cannot travel through black paper. Light has longer wavelengths and lower frequency than X-rays.
(c) An electromagnetic Spectrum is the distribution of frequencies of electromagnetic radiation such as radio waves, microwaves, infrared, visible, ultraviolet, X-rays and Gamma rays.








3 (a) Radioactivity is the spontaneous disintegration of a nucleus with the emission of particles or electromagnetic radiations.
(b) The Curie's two Nobel prizes:
1) In 1899, the Curries isolated a substance whose radioactivity was several hundred times that of hydrogen. It was named Polonium, after their country Poland. Later they found a substance that was even more radioactive which was called radium. It was produced in very small quantities that it was only detected as an impurity. In 1902, the Curies extracted a visible quantity of radium. In 1903, the Curies shared a Nobel prize with Henery Becuerel.
2) The second Nobel prize was in 1911, for Chemistry for the discovery on new elements and for isolating radium and studying its chemical properties.
(c) Cathode Rays were discovered by Heinrich Geisseir. He found a way to partially evacuate a glass chamber. The apparatus was a gas discharge tube, with an opening to remover the gases. There was a negative electrode and a positive electrode and a source of high electric potential difference. When with electric current flows the positive end glows. This led to the discovery of cathode rays.

X-rays were discovered by a German physicist whose name was Wilhelm Roentgen. While studying crystals that glowed when placed near a glass discharge tube it was noticed that a screen glowed that was sensitive to electromagnetic radiation. It only glowed when the tube was operating. Some form of electromagnetic radiation was though to be produced from the cathode rays striking the anode. Since he was unsure of the nature of this radiation, he called them X-rays.

In 1896 a French physicist, Antoine Henry Becquerel discovered radioactivity when searching for a relationship between X-rays and visible florescence. He wrapped an photographic plate in black paper and placed a thin crystal of uranium potassium sulphate on the paper. He put this in a drawer knowing that sunlight was needed for making the uranium compound fluorescence. When this was later examined it was found that radiation from the uranium compound had exposed the photographic plate through the black paper. These were called Becquerel rays.

d)Alpha radiation: Has a helium nuclei, it has radioactive and charges of all forms of radiation. They have a positive charge with 2 protons and 2 neutrons. They have the slowest