varnished-glass tube – покрита лаком скляна трубка
charge of like sign – одноіменний заряд
to attract - притягувати
sensitive instrument – чуттєвий інструмент
glass-jar – скляна
fit – кріпити, з’єднувати
rod – прут, палиця
to suspend – вішати, призупиняти
to repel – відштовхувати
II. Read and translate the text.
An electroscope is a sensitive instrument for detecting small electric charges. It consists of a glass-jar closed with a stopper of insulating material in which is fitted a varnished glass-tube. A rod passes through the tube. of At the top of the rod there is a metal ball or disc and at the bottom the rod two pieces of gold leaf are suspended. When a charge is brought near the electroscope, a charge of opposite sign is induced on the metal ball, and a charge of the same sign appears on the two of the gold leaves. Since the two pieces of gold leaf now have charges of like sign, they repel each other.
As an example a negatively charges glass rod is brought to the electroscope. A positive charge is induced on the ball and a negative charge appears on the two pieces of gold leaf.
The polarity of a charge may be determined by means of an electroscope. We charge the electroscope negatively by touching the ball with a rod of hard rubber which is rubbed with flannel or silk. If the unknown charge is brought to the electroscope it will induce on the ball a charge of opposite polarity, and on the gold leaves a charge of the same polarity as that of the unknown charge. Therefore, if the unknown charge is negative, the gold leaves will repel each other; if it is positive, the will attract.
III. Answer the following questions.
1. What is an electroscope?2. What does it consist of?
3. Where does the rod pass?
4. Where is a metal ball?
5. Where are two pieces of gold leaf suspended?
6. By what may be determined the polarity of a charge?
7. What will do the gold leaves if the unknown charge is negative?
IV. Read and translate the following word-combinations.
The gold leaves, the unknown charge, a charge of opposite polarity, the electroscope, flannel or silk, glass rod, a negative charge, a sensitive instrument, small electric charges, insulating material, a varnished glass-tube, the tube, a metal ball or disc, to repel, hard rubber, at the bottom of the rod.V. Continue the sentences.
1. An electroscope is a sensitive instrument for detecting ……………………………….2. At the top of the rod there is a metal ball or disc and at the bottom ……………………………………………
3. Since the two pieces of gold leaf now have charges of like sign ………………………
4. A positive charge is induced on the ball and …………………………………………….
5. The polarity of a charge may be determined by …………………………………….
6. If the unknown charge is brought to the electroscope it will …………………………….
7. If the unknown charge is negative, ……………………………………………………….