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Magnetism-and-Thermo-KEY

# Magnetism-and-Thermo-KEY - Version PREVIEW Magnetism and...

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Version PREVIEW – Magnetism and Thermo – Tubman – (3141) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. AP B 1998 MC 21 001 10.0 points An electron is in a uniform magnetic field B that is directed out of 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 left 4. toward the bottom of the page. correct 5. out of the page. 6. toward the top of the page. Explanation: The force on the electron is F = q v × B = - e v × B. The direction of the force is thus F = - v × B , pointing toward the bottom of the page , us- ing right hand rule for v × B , and reversing the direction due to the negative charge on the electron. Charged Particle in a Field 02 002 10.0 points A charged particle is projected with its initial velocity parallel to a uniform magnetic field. What is the resulting path? 1. straight line perpendicular to the field. 2. straight line parallel to the field. correct 3. parabolic arc. 4. spiral. 5. circular arc. Explanation: The force on a moving charge due to a magnetic field is given by F = q v × B . If v and B are parallel, then v × B = 0 . Hence the force on the particle is zero, and the particle continues to move in a straight line parallel to the field. Conceptual 17 02 003 (part 1 of 4) 10.0 points The strength of Earth’s magnetic field B at the equator is approximately equal to 5 × 10 - 5 T (tesla, the unit of a magnetic field). The force on a charge q moving 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 8 × 10 - 9 C. If you are at the equator and driving west at a speed of 30 m / s, what is the strength of the magnetic force on your head due to Earth’s magnetic field? Correct answer: 1 . 2 × 10 - 11 N. Explanation: Let : q = 8 × 10 - 9 C , v = 30 m / s , and B = 5 × 10 - 5 T .

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Version PREVIEW – Magnetism and Thermo – Tubman – (3141) 2 F = q v B = (8 × 10 - 9 C) (30 m / s) (5 × 10 - 5 T) = 1 . 2 × 10 - 11 N . 004 (part 2 of 4) 10.0 points What is the direction of that magnetic force? 1. downward 2. west 3. south 4. east 5. upward correct 6. north Explanation: Applying the right-hand rule, the direction of the magnetic force is upward. 005 (part 3 of 4) 10.0 points If you are at the equator and driving north at a speed of 30 m / s, what is direction of the magnetic force on your head? 1. There is no force. correct 2. north 3. upward 4. south 5. east 6. west 7. downward Explanation: The force is zero when your velocity is par- allel to the magnetic field.
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Magnetism-and-Thermo-KEY - Version PREVIEW Magnetism and...

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