1. At some automobile toll-collecting stations, a thin metal wire sticks up from the road and makes contact with cars before they reach the toll collector. What is the purpose of this wire?
2. The leaves of a charged electroscope collapse in time. At higher altitudes they collapse more rapidly. Why is this true? (Hint: The existence of cosmic rays was first indicated by this observation.)
3. In a crystal of salt are electrons and positive ions. How does the net charge of the electrons compare with the net charge of the ions? Explain.
4. It is relatively easy to strip the outer electrons from a heavy atom like that of uranium (which then becomes a uranium ion) but very difficult to remove the inner electrons. Why do you suppose this is so?
The electric force is stronger when the electron is closer to the nucleus
1. The purpose of the thin metal wire sticking up from the road at automobile toll-collecting stations is to detect the presence of a vehicle and trigger the toll collection process. When a car drives over the wire, it completes an electrical circuit, and this action is sensed by the toll system, signaling the collection of the toll.
2. The leaves of a charged electroscope collapse over time due to a process called ionization. The presence of charged particles, such as cosmic rays, in the atmosphere can cause ionization. At higher altitudes, the density of cosmic rays is usually higher, leading to more ionization events. This increased ionization accelerates the discharge of the electroscope's leaves, causing them to collapse more rapidly.
3. In a crystal of salt, the net charge of the electrons is equal to the net charge of the positive ions. This is because in an electrically neutral crystal, the positive charge of the ions balances out the negative charge of the electrons. Each sodium ion in a salt crystal has a positive charge, while each chlorine ion has a negative charge. The total number of positive charges from the ions is precisely balanced by the total number of negative charges from the electrons, resulting in a net charge of zero.
4. It is relatively easy to strip the outer electrons from a heavy atom like uranium because the outermost electrons, also known as valence electrons, are farther from the nucleus and therefore experience weaker attractive forces. These valence electrons are held less tightly by the positively charged nucleus, making it easier to remove them and form a uranium ion.
On the other hand, the inner electrons are closer to the nucleus and are shielded by the outer electrons. This means they experience stronger attractive forces from the positively charged nucleus. As a result, it is more difficult to remove these inner electrons because they are held more firmly by the nuclear charge. Additionally, the inner electrons play a crucial role in stabilizing the atom, so removing them would significantly disrupt the atom's structure.