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Unformatted text preview: johnson (rj6247) hw 9 Opyrchal (121014) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An electron in a vacuum is first accelerated by a voltage of 54300 V and then enters a region in which there is a uniform magnetic field of . 556 T at right angles to the direction of the electrons motion. What is the force on the electron due to the magnetic field? Correct answer: 1 . 23115 10 11 N. Explanation: Let : V = 1 . 38206 10 8 m / s and B = 0 . 556 T . The kinetic energy gained after acceleration is KE = 1 2 m e v 2 = q e V , so the velocity is v = radicalbigg 2 q e V m = radicalBigg 2(1 . 60218 10 19 C)(54300 V) 9 . 10939 10 31 kg = 1 . 38206 10 8 m / s . Then the force on it is f = qvB = (1 . 60218 10 19 C) (1 . 38206 10 8 m / s)(0 . 556 T) = 1 . 23115 10 11 N . 002 10.0 points A negatively charged particle moving paral- lel to the x-axis enters a magnetic field (point- ing into of the page), as shown in the figure below. x y v z vector B vector B q Figure: is in the x-direction, is in the y-direction, and k is in the z-direction. What is the initial direction of deflection? 1. hatwide F = + 2. hatwide F = + k 3. hatwide F = k 4. vector F = 0 ; no deflection 5. hatwide F = + 6. hatwide F = 7. hatwide F = correct Explanation: Basic Concepts: Magnetic Force on a Charged Particle: vector F = qvectorv vector B Right-hand rule for cross-products. hatwide F vector F bardbl vector F bardbl ; i.e. , a unit vector in the F direc- tion. Solution: The force is vector F = qvectorv vector B . vector B = B parenleftBig k parenrightBig , vectorv = v (+ ) , and q < , therefore , vector F = | q | vectorv vector B = | q | v B bracketleftBig (+ ) parenleftBig k parenrightBigbracketrightBig = | q | v B ( ) hatwide F = . johnson (rj6247) hw 9 Opyrchal (121014) 2 This is the third of eight versions of the problem. 003 10.0 points A positively charged particle moving paral- lel to the z-axis enters a magnetic field (point- ing toward the right-hand side of the page), as shown in the figure below. z x v y vector B vector B + q Figure: is in the x-direction, is in the y-direction, and k is in the z-direction. What is the initial direction of deflection? 1. hatwide F = + 2. vector F = 0 ; no deflection correct 3. hatwide F = + 4. hatwide F = 5. hatwide F = k 6....
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- Spring '08