IV. Match (21-30) with their definitions (A-L). There are two definitions that you do not need to use.

21.	line	A.	an electrode through which electric current flows out of a polarized electrical device
22.	ray	B.	a way of doing an activity which needs skill
23.	mass	C.	a connection between two points
24.	cathode	D.	the measure of the ability of a material to conduct either electricity or heat.
25.	theory	E.	a list of the substances that something is made of
26.	technique	F.	the amount of material in an object that stays the same no matter what force is acting on the object
27.	conductivity	G.	a small localized object to which can be ascribed several physical properties such as volume or mass
28.	discharge	H.	finding something or someone for the first time
29.	particle	I.	a formal statement of the rules on which a subject of study is based
30.	discovery	J.	a homogeneous mixture composed of only one phase
		K.	the release of an electric charge, or the equalization of an electric potential difference.
		L.	a narrow beam of light, heat, or energy

Supplementary Tasks :

I. For statements (1-10) choose the best alternative (A, B or C) to replace the expressions in italics:

1. ... which led him, in 1897, to the inference that all matter ... (line 2)

A.reasoningB.contributionC.discovery

2. ... although he originally called them corpuscles... (line 5)

A.initially B. finally C.lately

3. ... was the result of an attempt to solve a long-standing controversy (line 7)

A.initiativeB.ideaC.effort

4. Nearly all German physicists of the time held that these visible rays ... (line 11)

A.verifiedB.provedC.admitted

5. By applying an improved vacuum technique ... (line 16)

A.purified B. amended C.sophisticated

6. ... that these rays were composed of particles (line 17).

A. produced B. made C. made up

7. Thomson’s conclusion that the corpuscles were present in all kinds of matter ...(line 20)

A.inferenceB.confidenceC.saying

8. Although some atoms contain many electrons ... (line 32)

A.includeB.controlC.supervise

9. ...the scientific world had fully accepted Thomson’s far-reaching discovery (line 28).

A.disagreed B. supposed C. acknowledged

10. ... his hypothesis foreshadowed Einstein’s later theory of photons (line 32).

A. developed B. supported C.heralded

II. Determine the key message of the text. Choose the best alternative (A, B, C, D or E):

A. An attempt to discover the nature of cathode rays proved that they consisted of the same particles that were later called electrons.

B. The discovery of corpuscles was proved by many scientists in the field of physics.

C. The smallest particles of matter are electrons, their mass can’t achieve much than 1/1000 of the mass of atoms.

D. Electrons have the same size and properties in matter.

E. Thompson’s discovery made a great contribution to physics.

TEXT 12

CLASSICAL CYCLOTRONS

(1)The key to the operation of a cyclotron is the fact that the orbits of ions in a uniform magnetic field are isochronous; that is, the time taken by a particle of a given mass to make one complete circuit is the same at any speed or energy as long as the speed is much less than that of light. (As the speed of a particle approaches that of light, its mass increases). This isochronicity makes it possible for a high voltage, reversing in polarity at a constant frequency, to accelerate a particle many times. (2)An ion source is located at the centre of an evacuated chamber that has the shape of a short cylinder, like a pillbox, between the poles of an electromagnet that creates a uniform field perpendicular to the flat faces. The accelerating voltage is applied by electrodes, called dees from their shape: each is a D-shaped half of a pillbox. (3)The source of the voltage is an oscillator that operates at a frequency equal to the frequency of revolution of the particles in the magnetic field. The electric fields caused by this accelerating voltage are concentrated in the gap between the dees; there is no electric field inside the dees. The path of the particle inside the dees is therefore circular. Each time the particle crosses the gap, it is accelerated, because in the time between these crossings the direction of the field reverses. The path of the particle is thus a spiral-like series of semicircles of continually increasing radius. (4)Some means of focusing is required; otherwise, a particle that starts out in a direction making a small angle with the orbital plane will spiral into the dees and be lost. While the energy of the particle is still low, this focusing is supplied by the accelerating electric fields; after the particle has gained significant energy, focusing is a consequence of a slight weakening of the magnetic field toward the peripheries of the dees. (5)The energy gained by a particle in a classical cyclotron is limited by the relativistic increase in the mass of the particle, a phenomenon that causes the orbital frequency to decrease and the particles to get out of phase with the alternating voltage. This effect can be reduced by applying higher accelerating voltages to shorten the overall acceleration time. The highest energy imparted to protons in a classical cyclotron is less than 25 MeV, and this achievement requires the imposition of hundreds of kilovolts to the dees. The beam current in a classical cyclotron operated at high voltages can be as high as five milliamperes.