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Unformatted text preview: honea (cth632) H5Magnetism avram (1956) 1 This print-out should have 33 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An electron is in a uniform magnetic field B that is directed into the plane of the page, as shown. v e B B B B When the electron is moving in the plane of the page in the direction indicated by the arrow, the force on the electron is directed 1. into the page. 2. toward the right 3. toward the top of the page. 4. toward the bottom of the page. correct 5. toward the left 6. out of the page. Explanation: The force on the electron is vector F = q vectorv vector B = e vectorv vector B. The direction of the force is thus hatwide F = hatwide v hatwide B , pointing toward the bottom of the page , us- ing right hand rule for hatwide v hatwide B , and reversing the direction due to the negative charge on the electron. 002 (part 1 of 4) 10.0 points The strength of Earths magnetic field B at the equator is approximately equal to 5 10 5 T. The force on a charge q mov- ing in a direction perpendicular to a magnetic field is given by F = q v B , where v is the speed of the particle. The direction of the force is given by the right-hand rule. Suppose you rub a balloon in your hair and your head acquires a static charge of 1 10 9 C. If you are at the equator and driving west at a speed of 50 m / s, what is the strength of the magnetic force on your head due to Earths magnetic field? Correct answer: 2 . 5 10 12 N. Explanation: Let : q = 1 10 9 C , v = 50 m / s , and B = 5 10 5 T . F = q v B = (1 10 9 C) (50 m / s) (5 10 5 T) = 2 . 5 10 12 N . 003 (part 2 of 4) 10.0 points What is the direction of that magnetic force? 1. downward correct 2. upward 3. west 4. north 5. east 6. south Explanation: Applying the right-hand rule, the direction of the magnetic force is downward, since the Earths magnetic field points toward magnetic North, and the velocity is Westward. 004 (part 3 of 4) 10.0 points honea (cth632) H5Magnetism avram (1956) 2 If you are at the equator and driving north at a speed of 50 m / s, what is direction of the magnetic force on your head? 1. There is no force. correct 2. north 3. upward 4. east 5. west 6. south 7. downward Explanation: The force is zero when your velocity is par- allel to the magnetic field. 005 (part 4 of 4) 10.0 points If you are driving east, how fast would you have to drive in order for the magnetic force on your head to equal 190 N (probably enough to knock you over)? Correct answer: 3 . 8 10 15 m / s. Explanation: Let : F = 190 N , q = 1 10 9 C , and B = 5 10 5 T ....
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