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Unformatted text preview: Solution for Practice Test 8 for Test 3 Solution to Practice Test Problem 8.1(Field of Stationary Charge) Problem: A positive charge is fixed at the origin. What is the direction of the magnetic field at a point P at +1cmˆy ? Select One of the Following: (a) + x (b) x (c) + y (d) y (e) + z (f) z (gAnswer) Zero. Solution Zero. Only moving charge produces field. Total Points for Problem: 2 Points Solution to Practice Test Problem 8.2(Current Induced in Conducting Ring) Problem: The figure to the right shows a magnetic field whose strength is increasing with time and whose direction is into the page. What is the direction of the induced current in the con ducting ring (shown as a dark circle)? Select One of the Following: (a) Clockwise (b) Out of the page. (c) Into the page. (dAnswer) Counterclockwise. (e) There is no induced current. Magnetic Field Increasing in Strength Solution To oppose the increasing flux into the page, a magnetic field out of the page will be created by the induced current. Using the right hand rule for a wire, this gives the direction of induced current flow as counterclockwise. Total Points for Problem: 2 Points 1 Solution to Practice Test Problem 8.3(Force on Telephone Wire) Problem: The telephone poles through my backyard are about 25m apart. Assume the power wires carry about 1000A and that they run EastWest. In Arkansas the magnitude of the Earth’s magnetic field is 4 × 10 5 T . What is the total magnetic force on the power line between two telephone poles? Select One of the Following: (a) 25N . (b) . 04N . (c) 10N . (dAnswer) 1N . (e) There is no magnetic force. Solution The force on a current carrying wire is vector F = I vector ℓ × vector B = IℓB since the wire is perpendicular to the field, therefore F = IℓB = (1000A)(25m)(4 × 10 5 T) = 1N Total Points for Problem: 2 Points Solution to Practice Test Problem 8.4(Why Does Wire Deflect?) Problem: If lab, you performed an experiment on something I called a “magnetic pith ball” where an aluminum rod was suspended by copper wire so it hung in one of the big lab magnets. When a current was run through the circuit, the rod deflected. This happened because of which of the following physical laws? Select One of the Following: (a) Gauss’ Law. (b) Ampere’s Law. (c) Faraday’s Law. (dAnswer) The Lorentz force. (e) Heisenburg Uncertainty Principle. Solution The Lorentz Force. Total Points for Problem: 2 Points Solution to Practice Test Problem 8.5(Radius of Electron Orbit) Problem: The electrons in cosmic rays enter the atmosphere at about the speed of light, 3 × 10 8 m s . The Earth’s magnetic field is 4 × 10 5 T . An electron has charge 1 . 6 × 10 19 C and mass 9 . 11 × 10 31 kg . Neglecting relativistic corrections, what is the radius of the orbit of the electrons?...
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This note was uploaded on 05/04/2008 for the course PHYS 2074 taught by Professor Stewart during the Spring '08 term at Arkansas.
 Spring '08
 Stewart
 Physics, Charge

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