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.
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 (14th Edition)
Additional Science Textbook Solutions
Cosmic Perspective Fundamentals
Physics (5th Edition)
Essential University Physics: Volume 2 (3rd Edition)
Life in the Universe (4th Edition)
An Introduction to Thermal Physics
- Is Ampere’s law valid for all closed paths? Why isn’t it normally useful for calculating a magnetic field?arrow_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 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_forward
- 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_forwardUsing 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_forwardExplain why B=0 inside a long, hollow copper pipe that is carrying an electric current parallel to the axis. Is B=0 outside the pipe?arrow_forward
- A 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_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_forwardIn a region of space, a magnetic field is uniform over space but increases at a constant rate. This changing magnetic field induces an electric field that (a) increases in time, (b) is conservative, (c) is in the direction of the magnetic field, or (d) has a constant magnitude.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 rectangular conducting loop is placed near a long wire carrying a current I as shown in Figure OQ23.5. If I decreases in time, what can be said of the current induced in the loop? (a) The direction of the current depends on the size of the loop. (b) The current is clockwise. (c) The current is counterclockwise. (d) The current is zero. (e) Nothing can be said about the current in the loop without more information.arrow_forwardDesign a current loop that, when rotated in a uniform magnetic field of strength 0.10 T, will produce an emf =0 sin t. where 0=110V and 0=110V .arrow_forward
- Principles of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781285737027Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning
- Glencoe Physics: Principles and Problems, Student...PhysicsISBN:9780078807213Author:Paul W. ZitzewitzPublisher:Glencoe/McGraw-HillPhysics for Scientists and Engineers with Modern ...PhysicsISBN:9781337553292Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning