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The electroscope leaves can also be charged without touching a charged object to the terminal, by electrostatic induction. As the charged object is brought near the electroscope terminal, the leaves spread apart, because the electric field from the object induces a charge in the conductive electroscope rod and leaves, and the charged leaves ...
The needle turns to point at a nearby charged object due to charges induced in the ends of the needle by the external charge, through electrostatic induction.For example, if a positively charged object is brought near, the mobile negative charges in the metal will be attracted to it, and move to the end of the needle nearest the object.
A charged object outside any container also induces an equal charge on its surroundings. [12] [21] The field lines extending from it end on charges induced in the walls or other objects in the room. This illustrates the general principle that for every positive charge, there must be a corresponding negative charge somewhere in the universe.
[4]: p.711–713 If, while it is close to the positive charge, the above object is momentarily connected through a conductive path to electrical ground, which is a large reservoir of both positive and negative charges, some of the negative charges in the ground will flow into the object, under the attraction of the nearby positive charge. When ...
English: Diagram showing how a pith-ball electroscope works. The molecules (yellow ovals) that make up the pith ball (A) consist of positive charges (atomic nuclei) and negative charges (electrons) close together. Bringing a charged object (B) near the pith ball causes these charges to separate
Crookes X-ray tube from around 1910 Another Crookes x-ray tube. The device attached to the neck of the tube (right) is an "osmotic softener". When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, [16] it can accelerate the electrons to a high enough velocity to create X-rays when they hit the anode or the glass wall of the tube.
The terms anode and cathode are not defined by the voltage polarity of electrodes, but are usually defined by the direction of current through the electrode. An anode usually is the electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode usually is the electrode through which conventional current flows out of ...
The positive ions were accelerated by the electric field toward the cathode, and when they collided with it they knocked electrons out of its surface; these were the cathode rays. Modern vacuum tubes use thermionic emission , in which the cathode is made of a thin wire filament which is heated by a separate electric current passing through it.