Physics (5th Edition)
Physics (5th Edition)
5th Edition
ISBN: 9780321976444
Author: James S. Walker
Publisher: PEARSON
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Chapter 23, Problem 96PP

Loop Detectors on Roadways

“Smart” traffic lights are controlled by loops of wire embedded in the road (Figure 23). These “loop detectors” sense the change in magnetic field as a large metal object—such as a car or a truck—moves over the loop. Once the object is detected, electric circuits in the controller check for cross traffic, and then turn the light from red to green.

Chapter 23, Problem 96PP, Loop Detectors on Roadways Smart traffic lights are controlled by loops of wire embedded in the road

A typical loop detector consists of three or four loops of 14-gauge wire buried 3 in. below the pavement. You can see the marks on the road where the pavement has been cut to allow for installation of the wires. There may be more than one loop detector at a given intersection; this allows the system to recognize that an object is moving as it activates first one detector and then another over a short period of time. If the system determines that a car has entered the intersection while the light is red, It can activate one camera to take a picture of the car from the front—to see the driver’s face—and then a second camera to take a picture of the car and its license plate from behind This red-light camera system was used to good effect during an exciting chase scene through the streets of London in the movie National Treasure Book of Secrets.

Motorcycles are small enough that they often fail to activate the detectors, leaving the cyclist waiting and waiting for a green light. Some companies have begun selling powerful neodymium magnets to mount on the bottom of a motorcycle to ensure that they are “seen” by the detectors.

• Suppose the downward vertical component of the magnetic field increases as a car drives over a loop detector. As viewed from above, is the induced current in the loop clockwise, counterclockwise, or zero?

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Chapter 23 Solutions

Physics (5th Edition)

Ch. 23 - Explain the difference between a magnetic field...Ch. 23 - A metal ring with a break in its perimeter is...Ch. 23 - Many equal-arm balances have a small metal plate...Ch. 23 - Figure 23-29 shows a vertical iron rod with a wire...Ch. 23 - A metal rod of resistance R can slide without...Ch. 23 - Recently, NASA tested a power generation system...Ch. 23 - Explain what happens when the angular speed of the...Ch. 23 - A 0 085-T magnetic field passes through a circular...Ch. 23 - A uniform magnetic field of 0.0250 T points...Ch. 23 - A magnetic field is oriented at an angle of 67 to...Ch. 23 - MRI Solenoid The magnetic field produced by an MRI...Ch. 23 - Find the magnitude of the magnetic flux through...Ch. 23 - At a certain location, the Earths magnetic field...Ch. 23 - A solenoid with 385 turns per meter and a diameter...Ch. 23 - A single-turn square loop of side L is centered on...Ch. 23 - A bar magnet is inside a closed cubical box...Ch. 23 - A 0.65-T magnetic field is perpendicular to a...Ch. 23 - Prob. 11PCECh. 23 - Figure 23-33 shows the magnetic flux through a...Ch. 23 - One type of antenna for receiving AM radio signals...Ch. 23 - A wire loop is placed in a magnetic field that is...Ch. 23 - Figure 23-35 shows four different situations in...Ch. 23 - Predict/Calculate The magnetic flux through a...Ch. 23 - Prob. 17PCECh. 23 - A single conducting loop of wire has an area of...Ch. 23 - The area of a 120-turn coil oriented with its...Ch. 23 - An emf is induced in a conducting loop of wire...Ch. 23 - A magnetic field increases from 0 to 0.55 T in 16...Ch. 23 - Predict/Explain A metal ring is dropped into a...Ch. 23 - Predict/Explain A metal ring is dropped into a...Ch. 23 - Predict/Explain Figure 23-37 shows two metal disks...Ch. 23 - Predict/Explain (a) As the solid metal disk in...Ch. 23 - A bar magnet with its north pole pointing downward...Ch. 23 - A Wire Loop and a Magnet A loop of wire is dropped...Ch. 23 - Suppose we change the situation shown in Figure...Ch. 23 - Figure 23-39 shows a current-carrying wire and a...Ch. 23 - Consider the physical system shown in Figure...Ch. 23 - Prob. 31PCECh. 23 - Prob. 32PCECh. 23 - Prob. 33PCECh. 23 - A conducting rod slides on two wires in a region...Ch. 23 - A metal rod 0.95 m long moves with a speed of 2.4...Ch. 23 - Airplane emf A Boeing KC-135A airplane has a...Ch. 23 - Predict/Calculate Figure 23-42 shows a...Ch. 23 - Referring to part (a) of Problem 37, (a) find the...Ch. 23 - (a) Find the current that flows in the circuit...Ch. 23 - Suppose the mechanical power delivered to the rod...Ch. 23 - Prob. 41PCECh. 23 - A rectangular coil 25 cm by 45 cm has 150 turns....Ch. 23 - A 1 6-m wire is wound into a coil with a radius of...Ch. 23 - Shake Flashlight A shake flashlight uses the...Ch. 23 - Predict/Calculate A circular coil with a diameter...Ch. 23 - A generator is designed to produce a maximum emf...Ch. 23 - Prob. 47PCECh. 23 - Prob. 48PCECh. 23 - Prob. 49PCECh. 23 - Prob. 50PCECh. 23 - Prob. 51PCECh. 23 - Prob. 52PCECh. 23 - Prob. 53PCECh. 23 - A simple RL circuit includes a 0.125-H inductor....Ch. 23 - Prob. 55PCECh. 23 - Prob. 56PCECh. 23 - Prob. 57PCECh. 23 - Prob. 58PCECh. 23 - Prob. 59PCECh. 23 - Prob. 60PCECh. 23 - Prob. 61PCECh. 23 - Alcator Fusion Experiment In the Alcator fusion...Ch. 23 - Superconductor Energy Storage An engineer proposes...Ch. 23 - Prob. 64PCECh. 23 - Prob. 65PCECh. 23 - Prob. 66PCECh. 23 - Transformer 1 has a primary voltage Vp and a...Ch. 23 - The electric motor in a toy train requires a...Ch. 23 - Predict/Calculate A disk drive plugged into a...Ch. 23 - A transformer with a turns ratio...Ch. 23 - A neon sign that requires a voltage of 11,000 V is...Ch. 23 - A step-down transformer produces a voltage of 6.0...Ch. 23 - A step-up transformer has 30 turns on the primary...Ch. 23 - CE Predict/Explain An airplane flies level to the...Ch. 23 - CE You hold a circular loop of wire at the north...Ch. 23 - Prob. 76GPCh. 23 - Interstellar Magnetic Field The Voyager I...Ch. 23 - Prob. 78GPCh. 23 - BIO Electrognathography Computerized jaw tracking,...Ch. 23 - A rectangular loop of wire 24 cm by 72 cm is bent...Ch. 23 - Consider a rectangular loop of wire 6.8 cm by 9.2...Ch. 23 - Predict/Calculate A car with a vertical radio...Ch. 23 - The rectangular coils in a 355-tum generator are...Ch. 23 - A cubical box 22 cm on a side is placed in a...Ch. 23 - BIO MRI Scanner An MRI scanner is based on a...Ch. 23 - BIO Transcranial Magnetic Stimulation Transcranial...Ch. 23 - A magnetic field with the time dependence shown in...Ch. 23 - Prob. 88GPCh. 23 - Prob. 89GPCh. 23 - Prob. 90GPCh. 23 - BIO Blowfly Maneuvers Suppose the fly described in...Ch. 23 - Prob. 92GPCh. 23 - Predict/Calculate A single-turn rectangular loop...Ch. 23 - Prob. 94GPCh. 23 - Prob. 95GPCh. 23 - Loop Detectors on Roadways Smart traffic lights...Ch. 23 - A car drives onto a loop detector and increases...Ch. 23 - A truck drives onto a loop detector and increases...Ch. 23 - Loop Detectors on Roadways Smart traffic lights...Ch. 23 - Referring to Conceptual Example 23-6 Suppose the...Ch. 23 - Referring to Conceptual Example 23-6 Suppose the...Ch. 23 - Referring to Example 23-8 (a) What external force...Ch. 23 - Predict/Calculate Referring to Example 23-8...
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Magnets and Magnetic Fields; Author: Professor Dave explains;https://www.youtube.com/watch?v=IgtIdttfGVw;License: Standard YouTube License, CC-BY