No visual, use rest of rubric) \"Smart\" traffic lights are controlled by loops

Question

No visual, use rest of rubric) "Smart" traffic lights are controlled by loops of wire embedded in the road. These "loop detectors detect the change in the Earth's magnetic field as a large metal object such as a car or truck - moves over the loop. Suppose a loop detector is circular with a diameter of 3.0 feet (convert to m) As a car passes over the detector, the downward magnetic field within the loop increases from 1.5 x 10-5 T to 2.4 x 10-5 T in 0.52 seconds As viewed from above, what is the direction of the induced current in the loop? Explain. If the loop has 120 turns, what is the induced emf in the loop? No rubric) Consider the situation in the picture to the right. A ring falls from a region of zero field into a region of uniform field (1), then 2. o continues to fall until it exits the region of uniform field (3). In what direction does the current flow in: a. Position 1 Position 2 b. c. Position3 Explain your answers in each case.

Explanation / Answer

1.

as viewed from above, field is into the plane.

and fllux is increasing, so field due to induced current wil be out of page.

Current -> COunter clock wise

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e = N A dB/dt

e = (120) (pi (3 x 0.3048 / 2)^2) (2.4 - 1.5)(10^-5)/(0.52)

e = 1.52 x 10^-3 Volt Or 1.52 mV  

2. position 1: field is out of page and flux is increasing. So induced field will be into the page.

direction -> clockwise

position 2: no change in flux

so no current induced.

position 3: flux decrasing so induced field will be out of page

direction: counter clock wise

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