The Physics
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Opus in profectus

# Electromagnetic Induction

## Problems

### practice

1. Write something.
2. Write something.
3. Write something.
4. Write something completely different.

### conceptual

1. The diagram below shows a segment of a wire as it moves through a region of uniform magnetic field B. Show the direction of the induced current flow through the wire. 2. In what direction should the wire be moved through the magnetic field so as to induce the current indicated in the diagram below? 3. The diagram below shows the instantaneous position of a rotating loop of wire between two bar magnets. The loop is rotating clockwise when viewed from P. The magnets and the loop all lie in the same plane. Indicate the direction of induced current flow in the loop. 4. Some roads have large wire loops embedded in them just below the surface. The loops are about the size of a car, are oriented horizontal, and lie just below the surface of the pavement.
1. Describe the probable effect that driving a car over the loop would have on the loop.
2. What additional equipment would be needed to detect this effect?
3. What practical application might such a device have?
5. A pair of related questions.
1. How are an electric motor and electric generator similar? How are they different?
2. How are a dynamic loudspeaker and dynamic microphone similar? How are they different?
6. Why is wearing headphones outside during a thunderstorm a bad idea? Note: The answer is not that the headphones "attract" lightning.

### numerical

1. The Earth's magnetic field in the New York City area has a magnitude of 52.5 μT. It points generally north, but is deflected down 64.5° below the horizontal. A Boeing 747-400 with a wingspan of 64.4 m and wing area of 560 m2 is flying in this area due north at 275 m/s.
1. Determine the induced emf across the plane's wings.
2. Which wing tip is at the higher potential, the one on the west side of the plane or the one one the east side of the plane?
2. Magnetic resonance imaging (MRI) is a medical imaging technique that uses strong magnetic fields. Sliding a patient into or out of an MRI machine will result in a small induced current. An electric field across the human body of 6.2 V/m has been suggested as the threshold for nerve stimulation at low frequencies. How quickly would a person have to be pushed into a 4 T, whole body MRI to generate the threshold electric field? (Assume a person lying on their back has a height of 1.6 m and a width of 0.30 m.)
3. A 1×3 cm rectangular coil with 20 loops is rotated at a contant frequency of 60 Hz in a uniform magnetic field of 0.24 T. Determine the average emf induced in the coil on any half turn that begins with the coil capturing the maximumum possible magnetic flux.