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Unformatted text preview: Ch. 29/30 Practice Test — Solution Multiple Choice 1. (b) Torques from the magnetic force on the top and bottom wire cancel and any force on the wire on the left contributes no torque, so we only need to consider the wire on the right. Since everything is nice and perpendicular, τ = rF = rIlB = (0 . 3m)(2A)(0 . 3m)(0 . 05T) = 0 . 009N · m . 2. (b) Amp` ere-Maxwell equation: H B · ds = μ 0 0 dE dt . 3. (b) F c = F B , so mv 2 r = qvB , which shows that B and v are inversely proportional. 4. (e) Magnetic field inside an ideal solenoid is uniform. 5. (e) The magnetic field does no work because the force is always perpendicular to the velocity. 6. (b) ~ F B = I ~ l × ~ B = (15A)(2 . ˆ i )m × (30 ˆ i- 40 ˆ j )mT = [30 ˆ i × (- 40 ˆ j )]mN = (- 1200 ˆ k )mN = (- 1 . 20 ˆ k )N Alternatively, by the right hand rule, ~ F B points down. Its magnitude equals the area of the parallelogram created by I ~ l and ~ B , which has base length | I ~ l | = (15A)(2 . 0m) and height 40mT (the...
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- Spring '10
- Force, Magnetic Field, fb, Right-hand rule