WebAssign HW23-F15(CH23) (Homework)

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1 WebAssign HW23-F15(CH23) (Homework) Current Score : 29 / 29 Due : Friday, December :59 PM EST Jessica Avina PHYS272-FALL15, Fall 2015 Instructor: Virendra Saxena The due date for this assignment is past. Your work can be viewed below, but no changes can be made. Important! Before you view the answer key, decide whether or not you plan to request an extension. Your Instructor may not grant you an extension if you have viewed the answer key. Automatic extensions are not granted if you have viewed the answer key. View Key 1. 1/1 points Previous AnswersMI4 23.Q.001. Match each task below with the law that would be useful in analyzing the situation. (a) Find the magnetic field inside a current-carrying coaxial cable. Ampere-Maxwell law (b) Predict what an AC voltmeter reads whose leads encircle a coil. Faraday's law (c) Find the amount of charge inside a box. Gauss's law for electricity (d) Relate the magnetic flux on one face of a cube to the magnetic flux on the other faces. Gauss's law for magnetism Section 23.1 Page 1 of 10

2 2. 1/1 points Previous AnswersMI4 23.Q.002. At a time t 0 an electric field is detected in the region shown on the left diagram. The electric field is zero at all other locations. At a later time t 1 an electric field is detected in the region shown on the right diagram; the electric field is zero elsewhere. You conclude that an electromagnetic wave is passing through the region. (a) What is the direction of propagation of the electromagnetic wave? -y (b) If you were to measure the magnetic field in the region where the electric field is nonzero, what would be the direction of the magnetic field? -z (into page) Section /1 points Previous AnswersMI A pulse of electromagnetic radiation is propagating in the -y direction. You have two devices that can detect electric and magnetic fields. You place detector #1 at location < 0, 4, 0> m and detector #2 at location < 0, -4, 0> m. (a) At time t = 0, detector #1 detects an electric field in the -x direction. At that instant, what is the direction of the magnetic field at the location of detector #1? -z (b) At what time will detector #2 detect electric and magnetic fields? t = 2.67e-8 s Section 23.2 Page 2 of 10

3 4. 1/1 points Previous AnswersMI If the magnetic field in a particular pulse has a magnitude of tesla (comparable to the Earth's magnetic field), what is the magnitude of the associated electric field? 9000 V/m Section /1 points Previous AnswersMI A pulse of radiation propagates with velocity = < 0, 0, c >. The electric field in the pulse is = < , 0, 0 > N/C. What is the magnetic field in the pulse? = $$ 0, 0.031, 0 T Section /1 points Previous AnswersMI Electromagnetic radiation is moving to the right, and at this time and place the electric field is horizontal and points out of the page (see the figure). The magnitude of the electric field is E = 3000 N/C. What is the magnitude of the associated magnetic field at this time and place? B = 1e-5 T What is the direction of the associated magnetic field at this time and place? e Section 23.2 Page 3 of 10

4 7. 1/1 points Previous AnswersMI An electric field of 10 6 N/C acts on an electron, resulting in an acceleration of m/s 2 for a short time. What is the magnitude of the radiative electric field observed at a location a distance of 1 cm away along a line perpendicular to the direction of the acceleration? 2.24e-7 N/C Page 4 of 10

5 8. 1/1 points Previous AnswersMI A proton is accelerated in the direction shown by the arrow labeled. You want to calculate the magnitude and direction of the radiative electric field which will be observed at the location shown by the vector. In which of the following diagrams is the vector correctly shown by the red arrow? C A B C D E F 9. 5/5 points Previous AnswersMI A proton is briefly accelerated in the direction of the arrow labeled a in the figure below. The vector r indicates the location of an observation location relative to the initial position of the proton. The vector a for this observation location is indicated on the diagram. Page 5 of 10

6 (a) If θ is 38, and the magnitude of the acceleration is m/s 2, what is the magnitude of a?? 1.847e17 m/s 2 (b) What is the magnitude of the radiative electric field at the indicated observation location, if the magnitude of r is m? 1.97e-7 N/C (c) At the observation location, what is the direction of the radiative electric field? the same as the direction aof opposite to the direction aof the same as the direction aof opposite to the direction aof the same as the direction rof opposite to the direction rof into the page out of the page (d) At the observation location, what is the direction of the ordinary Coulomb electric field due to the proton? Page 6 of 10

7 the same as the direction aof opposite to the direction aof the same as the direction aof opposite to the direction aof the same as the direction rof opposite to the direction rof into the page out of the page (e) At the observation location, what is the direction of the radiative magnetic field? the same as the direction aof opposite to the direction aof the same as the direction aof opposite to the direction aof the same as the direction rof opposite to the direction rof into the page out of the page Page 7 of 10

8 10.3/3 points Previous AnswersMI A proton located at the origin is accelerated in the -y direction for a brief time. (a) How much time passes before a detector located at <0.25, 0, 0> m detects a radiative electric field? 8.3e-10 s (b) What is the direction of the radiative electric field observed at this location? +y (c) If the accelerated particle had been an electron instead of a proton, what would have been the direction of the radiative electric field at this location? -y 11.6/6 points Previous AnswersMI An accelerated electron An electron is initially at rest. At time t 1 = 0 it is accelerated upward with an acceleration of a = m/s 2 for a very short time (this large acceleration is possible because the electron has a very small mass). We make observations at location A, x = 18 meters from the electron (see the figure). (a) At time t 2 = 1 ns (10-9 s), what is the magnitude and direction of the electric field at location A due to the electron? magnitude: 4.4e-12 direction: N/C to the left upwards to the right zero field downwards (b) At what time t 3 does the electric field at location A change? 6e-8 seconds Page 8 of 10

9 (c) What is the direction of the electric field at location A at time t 3? downward zero field to the right to the left upward (d) What is the magnitude of this electric field? 8.89e-11 N/C (e) A positively charged particle was initially at rest at location A. It is released from rest just after time t 3. Which of the following are true just after time t 3? (Select all that apply.) The positive charge will never be affected by the radiative magnetic field, since the positive charge is always at rest. The radiative magnetic field at location A is out of the page. There is a magnetic force to the right on the positive charge. The positive charge begins to move because there is a force on it due to the radiative electric field. The electric force on the positive charge due to the radiative electric field is upward. The electric force on the positive charge is toward the electron. Page 9 of 10

10 12.7/7 points Previous AnswersMI (a) If the electric field inside a capacitor exceeds about V/m, the few free electrons in the air are accelerated enough to trigger an avalanche and make a spark. In the spark shown in the diagram, electrons are accelerated upward and positive ions are accelerated downward. Which arrow best indicates the direction of propagation of electromagnetic radiation reaching location B? c Which arrow best indicates the direction of propagation of electromagnetic radiation reaching location C? d What is the direction of the radiative electric field observed at location B? a What is the direction of the radiative electric field observed at location C? b What is the direction of the radiative magnetic field observed at location B? j What is the direction of the radiative magnetic field observed at location C? j If you are at location A, d = 7 meters to the left of the capacitor, how long after the initiation of the spark could you first detect a magnetic field? 2.33e-8 seconds Page 10 of 10