Week Five Textbook Exercises
December 9, 2014
Mr. Craig Spencer
Week Five Textbook Exercises
Chapter 22: Electrostatics
When combing your hair, you scuff electrons from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?
-The hair becomes positively charged and the comb becomes negatively charged; since, the electrons went from your hair to the comb and the more electrons there is makes an object more negative. 18)
It is relatively easy to strip the outer electrons from a heavy atom like that of uranium (which then becomes a uranium ion), but it is very difficult to remove the inner electrons. Why do you suppose this is so?
-Outer electrons are loosely bound with the nucleus because of their larger distance from the nucleus, so they can be easily stripped off. In the case of the inner electrons, the opposite is true. They are more tightly bound because their closer to the nucleus, so they are more difficult to remove them. 52)
You are not harmed by contact with a charged metal ball, even though its voltage may be very high. Is the reason similar to why you are not harmed by the greater than 1000ºC sparks from a Fourth of July sparkler? Defend your answer in terms of the energies that are involved.
-Yes. The reason is similar, because the amount of energies involved in both cases is very small.
Chapter 23: Electric Current
In the circuit shown, how do the brightnesses of the identical lightbulbs compare? Which bulb draws the most current? What will happen if Bulb A is unscrewed? If Bulb C is unscrewed?
-The brightness of Bulb A and Bulb B will be the same, while Bulb C will be twice as Bulbs A or B. Bulb C draws the most current. When Bulb A is unscrewed, Bulb C will glow as it had and Bulb B will not glow. If Bulb C is unscrewed, Bulb A and Bulb B will glow at the same brightness.
Chapter 24: Magnetism
One way to make a compass is to stick a magnetized needle into a piece of cork and float it in a glass bowl full of water. The needle will align itself with the horizontal component of Earth’s magnetic field. Since the north pole of this compass is attracted northward, will the needle float toward the north side of the bowl? Defend your answer.
-The needle will point toward the northward direction; however, it will not move towards the northward side since the forces acting on the needle balances each other out, remaining at rest. 43)
In a mass spectrometer, ions are directed into a magnetic field, where they curve and strike a detector. If a variety of singly ionized atoms travel at the same speed through the magnetic field, would you expect them all to be deflected by the same amount, or would different ions be bent different amounts? Defend your answers.
-Deflection of ions by magnetic fields solely depends upon their charge/mass ratio. This is different for different ions.
Chapter 25: Electromagnetic Induction
A certain simple earthquake detector consists of a little box firmly anchored to Earth. Suspended inside the box is a massive magnet that is surrounded by stationary coils of wire fastened to the bod. Explain how this device works, applying two important principles of physics—one studied in Chapter 2 and the other in this chapter.
-When an earthquake occurs, stationary coils inside the detector begin to vibrate and a relative motion between the coils and magnets is generated. The motion of the coils induces voltage into the coils. As a result, the intensity of the earthquake is recorded. 22)
A length of wire is bent into a closed loop and a magnet is plunged into it, inducing a voltage and, consequently, a current in the wire. A second length of wire, twice as long, is bent into two loops of wire, and a magnet is similarly plunged into it. Twice the voltage is induced, but the current is the same as that produced in the single loop. Why?
-The voltage induced is...
References: Hewitt, P.G. (2010). Conceptual Physics (11th ed.). St. Petersburg, FL: Pearson.
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