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HW01-solutions

# HW01-solutions - Munoz(gm7794 HW01 TSOI(92515 y This...

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Munoz (gm7794) – HW01 – TSOI – (92515) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points In a crystal of salt there are electrons and positive ions. How does the net charge of the electrons compare with the net charge of the ions? 1. The net charge of the negative electrons is greater than the net charge of the ions. 2. The net charge of the negative electrons has the same magnitude as the net charge of the ions. correct 3. Unable to determine 4. The net charge of the negative electrons is less than the net charge of the ions. 5. Sometimes the net charge of the negative electrons is greater than the net charge of the ions and sometimes it is less. Explanation: The crystal as a whole has a zero net charge, so any negative charge in one part is countered with the same amount of positive charge in another part. Therefore the net charge of the negative electrons has the same magnitude as the net charge of the ions. 002 10.0 points A circular ring made of an insulating material is cut in half. One half is given a charge - q uniformly distributed along its arc. The other half is given a charge + q also uniformly distributed along its arc. The two halves are then rejoined with insulation at the junctions J , as shown. x y - q + q J J - - - - - - - - - - - - - - - - - - + + + + + + + + ++ + + + + + + + + q e If there is no change in the charge distri- butions, what is the direction of the net elec- trostatic force on an electron located at the center of the circle? 1. To the left 2. Into the page 3. Toward the top of the page 4. Toward the bottom of the page correct 5. To the right Explanation: The rejoined system is symmetrical about the diameter perpendicular to the line con- necting two junctions. The electrostatic force is along the direction connecting the two charges (repulsive for charges of the same sign and attractive for charges of the oppo- site sign), so the force on the electron is paral- lel to the symmetrical axis and points toward the positive charge; i.e. , toward the bottom of the page. 003 10.0 points A strong lightning bolt transfers about 27 C to Earth. How many electrons are transferred? The charge on an electron is - 1 . 60218 × 10 - 19 C. Correct answer: 1 . 68521 × 10 20 . Explanation: Let : q = 27 C and

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Munoz (gm7794) – HW01 – TSOI – (92515) 2 q e = - 1 . 60218 × 10 - 19 C . The charge is proportional to the number of electrons, so q = n | q e | n = q | q e | = 27 C | - 1 . 60218 × 10 - 19 C | = 1 . 68521 × 10 20 . 004 10.0 points A charge of +1 Coulomb is place at the 0- cm mark of a meter stick. A charge of - 1 Coulomb is placed at the 100-cm mark of the same meter stick. Is it possible to place a proton somewhere on the meter stick so that the net force on it due to the two charges is 0? 1. Yes; to the left of the 50-cm mark 2. Yes; to the right of the 50-cm mark 3. No correct Explanation: The proton is repelled from the +1 Coulomb charge and attracted to the - 1 Coulomb charge. Both forces act in the same direction so they cannot cancel out.
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