In an electric trolley or bus system, the vehicle’s motor draws current from an overhead wire by means of a long arm with an attachment at the end that slides along the overhead wire. A brilliant electric spark is often seen when the attachment crosses a junction in the wires where contact is momentarily lost. Explain this phenomenon.
the phenomenon used in electric trolley system.
Explanation of Solution
The key terms explaining the electric trolley system is generation of standing waves and the back emf of the trolley motor.
In the above mentioned electric bus system the vehicle’s motor draws current from a single wire connection. The return current runs through the steel rails of the track.
As the train moves, the contact shoes (long arm) slides along the wire and this leads to generation of standing waves in the over head wires.
The standing waves occur because the medium (bus) is moving in the opposite direction to the wave. It can also rise due to interference between two waves travelling in opposite directions. These waves are reflected back and forth in the electric line.
With respect to Sparking, it occurs when there is loss of contact or improper contact between the long arm of the bus and the contact wire of the system. The under-lying mechanism is that it is due to the "back EMF" (reverse voltage) from the trolley motor, when contact is interrupted. That is this emf opposes the change in current which had earlier induced it. This concept is resourced from Lenz law.
Conclusion:
Thus, the mechanism of electric trolley system is explained.
Want to see more full solutions like this?
Chapter 30 Solutions
University Physics with Modern Physics, Volume 2 (Chs. 21-37); Mastering Physics with Pearson eText -- ValuePack Access Card (14th Edition)
Additional Science Textbook Solutions
Essential University Physics: Volume 1 (3rd Edition)
Cosmic Perspective Fundamentals
Conceptual Physics (12th Edition)
Physics for Scientists and Engineers with Modern Physics
- Using an electromagnetic flowmeter (Fig. P19.69), a heart surgeon monitors the flow rate of blood through an artery. Electrodes A and B make contact with the outer surface of the blood vessel, which has interior diameter 3.00 mm. (a) For a magnetic field magnitude of 0.040 0 T, a potential difference of 160 V appears between the electrodes. Calculate the speed of the blood. (b) Verify that electrode A is positive, as shown. Does the sign of the emf depend on whether the mobile ions in the blood are predominantly positively or negatively charged? Explain. Figure P19.69arrow_forwardReview. The use of superconductors has been proposed for power transmission lines. A single coaxial cable (Fig. P31.47) could carry a power of 1.00 103 MW (the output of a large power plant) at 200 kV, DC, over a distance of 1.00 103 km without loss. An inner wire of radius a = 2.00 cm, made from the superconductor Nb3Sn, carries the current I in one direction. A surrounding superconducting cylinder of radius b = 5.00 cm would carry the return current I. In such a system, what is the magnetic field (a) at the surface of the inner conductor and (b) at the inner surface of the outer conductor? (c) How much energy would he stored in the magnetic field in the space between the conductors in a 1.00 103 km superconducting line? (d) What is the pressure exerted on the outer conductor due to the current in the inner conductor? Figure P31.47arrow_forwardA thin wire = 30.0 cm long is held parallel to and d = 80.0 cm above a long, thin wire carrying I = 200 A and fixed in position (Fig. P30.47). The 30.0-cm wire is released at the instant t = 0 and falls, remaining parallel to the current-carrying wire as it falls. Assume the falling wire accelerates at 9.80 m/s2. (a) Derive an equation for the emf induced in it as a function of time. (b) What is the minimum value of the emf? (c) What is the maximum value? (d) What is the induced emf 0.300 s after the wire is released? Figure P30.47arrow_forward
- A straight wire of mass 10.0 g and length 5.0 cm is suspended from two identical springs that, in turn, form a closed circuit (Fig. P19.74). The springs stretch a distance of 0.50 cm under the weight of the wire. The circuit has a total resistance of 12 . When a magnetic field directed out of the page (indicated by the dots in the Figure) is turned on, the springs are observed to stretch an additional 0.30 cm. What is the strength of the magnetic field? (The upper portion of the circuit is fixed.) Figure P19.74arrow_forwardA metal bar of mass 500 g slides outward at a constant speed of 1.5 cm/s over two parallel rails separated by a distance of 30 cm which are pail of a U-shaped conductor. There is a uniform magnetic field of magnitude 2 T pointing out of the page over the entire area. The railing and metal bar have an equivalent resistance of 150 . (a) Determine the induced current, both magnitude and direction, (b) Find the direction of tire induced current if the magnetic field is pointing into the page, (c) Find the direction of the induced current if the magnetic field is pointed into the page and the bar moves inwards.arrow_forwardA flip coil is a relatively simple device used to measure a magnetic field, It consists of a circular coil of N turns wound with fine conducting wire. The coil is attached to a ballistic galvanometer, a device that measures the total charge that passes through it. The coil is placed in a magnetic field B such that its face is perpendicular to the field. It is then flipped through 180°, and tire total charge Q that flows through the galvanometer is measured. (a) If the total resistance of tire coil and galvanometer Is R, what is the relationship between B and Q? Because the coil is very small, you can assume that Bis uniform over it. (b) How can you determine whether or not tire magnetic field is perpendicular to the face of the coil?arrow_forward
- Review. Rail guns have been suggested for launching projectiles into space without chemical rockets. A tabletop model rail gun (Fig. P22.76) consists of two long, parallel, horizontal rails = 3.50 cm apart, bridged by a bar of mass m = 3.00 g that is free to slide without friction. The rails and bar have low electric resistance, and the current is limited to a constant I = 24.0 A by a power supply that is far to the left of the figure, so it has no magnetic effect on the bar. Figure P22.76 shows the bar at rest at the midpoint of the rails at the moment the current is established. We wish to find the speed with which the bar leaves the rails after being released from the midpoint of the rails. (a) Find the magnitude of the magnetic field at a distance of 1.75 cm from a single long wire carrying a current of 2.40 A. (b) For purposes of evaluating the magnetic field, model the rails as infinitely long. Using the result of part (a), find the magnitude and direction of the magnetic field at the midpoint of the bar. (c) Argue that this value of the field will be the same at all positions of the bar to the right of the midpoint of the rails. At other points along the bar, the field is in the same direction as at the midpoint, but is larger in magnitude. Assume the average effective magnetic field along the bar is five times larger than the field at the midpoint. With this assumption, find (d) the magnitude and (e) the direction of the force on the bar. (f) Is the bar properly modeled as a particle under constant acceleration? (g) Find the velocity of the bar after it has traveled a distance d = 130 cm to the end of the rails. Figure P22.76arrow_forwardA circuit consists of a conducting movable bar and a lightbulb connected to two conducting rails as shown in Figure OQ31.10. An external magnetic field is directed perpendicular to the plane of the circuit. Which of the following actions will make the bulb light up? More than one statement may be correct, (a) The bar is moved to the left, (b) The bar is moved to the right. (c) The magnitude of the magnetic field is increased. (d) The magnitude of the magnetic field is decreased. (e) The bar is lifted off the rails.arrow_forwardConsider the system pictured in Figure P28.26. A 15.0-cm horizontal wire of mass 15.0 g is placed between two thin, vertical conductors, and a uniform magnetic field acts perpendicular to the page. The wire is free to move vertically without friction on the two vertical conductors. When a 5.00-A current is directed as shown in the figure, the horizontal wire moves upward at constant velocity in the presence of gravity. (a) What forces act on the horizontal wire, and (b) under what condition is the wire able to move upward at constant velocity? (c) Find the magnitude and direction of the minimum magnetic Field required to move the wire at constant speed. (d) What happens if the magnetic field exceeds this minimum value? Figure P28.26arrow_forward
- How can you decide if a wire is infinite?arrow_forward(a) What is the speed of a supersonic aircraft with a 17.0-m wingspan, if it experiences a 1.60V Hall voltage between its wing lips when in level flight over the north magnetic pole, where the Earth's field strength is 8.00105T ? (b) Explain why very little current flows as a result of this Hall voltage.arrow_forwardSuppose you have a long, skinny conductor that is oriented with its long axis parallel to a uniform magnetic field. Suppose also that the conductor is moving along its long axis in a straight line at constant velocity v. Despite the motion of the conductor, no motional emf is induced. Why? The magnetic field is too uniform The velocity has no component normal to the magnetic field The velocity is too low The conductor is so long and so thin that its electrical resistance is too higharrow_forward
- College PhysicsPhysicsISBN:9781285737027Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning
- Principles of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningGlencoe Physics: Principles and Problems, Student...PhysicsISBN:9780078807213Author:Paul W. ZitzewitzPublisher:Glencoe/McGraw-HillPhysics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning