Chapter 19 - CHAPTER 19 Quick Quizzes 1. (b). The force...

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C HAPTER 19 Quick Quizzes 1. (b). The force that a magnetic field exerts on a charged particle moving through it is given by sin Fq v B q v B θ == , where B is the component of the field perpendicular to the particle’s velocity. Since the particle moves in a straight line, the magnetic force (and hence B , since ) must be zero. 0 qv 2. (c). The magnetic force exerted by a magnetic field on a charge is proportional to the charge’s velocity relative to the field. If the charge is stationary, as in this situation, there is no magnetic force. 3. (a). The magnetic force acting on the particle is always perpendicular to the velocity of the particle, and hence to the displacement the particle is undergoing. Under these conditions, the force does no work on the particle and the particle’s kinetic energy remains constant. 4. (c). Anytime the velocity of a charged particle is perpendicular to the magnetic field, it will follow a circular path. The two particles will move in opposite directions around their circular paths if their charges have opposite signs, but their charges are unknown so (d) is not an acceptable answer. 5. (b). The two forces are an action-reaction pair. They act on different wires, and have equal magnitudes but opposite directions. 125
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CHAPTER 19 Problem Solutions 19.1 The direction in parts (a) through (d) is found by use of the right hand rule. You must remember that the electron is negatively charged, and thus experiences a force in the direction exactly opposite that predicted by the right hand rule for a positively charged particle. (a) horizontal and due east (b) horizontal and 30 N of E ° (c) (d) zero force , () si ns i n180 0 Fq v B q v B θ = = 19.2 (a) For a positively charged particle, the direction of the force is that predicted by the right hand rule. These are: (a’) in plane of page and to left (b’) into the page (c’) out of the page ( d ) in plane of page and tow ard the top (e’) (f’) (b) For a negatively charged particle, the direction of the force is exactly opposite what the right hand rule predicts for positive charges. Thus, the answers for part (b) are reversed from those given in part (a) . 19.3 Since the particle is positively charged, use the right hand rule. In this case, start with the thumb of the right hand in the direction of v and the palm facing the direction of F . The fingers will point in the direction of B . The results are (a) (b) tow ard the right (c) tow ard bottom of page 19.4 Hold the right hand with the thumb in the direction of v and the fingers in the direction of B . The palm will the face the direction of the force (and hence the deflection) if the particle has a positive charge. The results are (a) tow ard top of page (b) , since the charge is negative. (c) (d) 126
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CHAPTER 19 19.5 Gravitational force: ( ) ( ) 31 2 9.11 10 kg 9.80 m s g Fm g == × = 30 8.93 N downward × Electric force: ( ) ( ) 19 1.60 C 100 N C e Fq E == − × = 17 N upw ard × Magnetic force: ( ) ( )( ) ( ) 6 6 si n1 .
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This homework help was uploaded on 03/21/2008 for the course PY 211 / 212 taught by Professor Chilton during the Spring '08 term at N.C. State.

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Chapter 19 - CHAPTER 19 Quick Quizzes 1. (b). The force...

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