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PY208N-Lecture-21

# PY208N-Lecture-21 - Physics 208N-004 Lecture#21 4 March...

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1 Physics 208N-004 Lecture #21 – 4 March 2011 Chapter 29: 3-7 – Motion EMF andTransformers This image shows another way the magnetic flux can change: The induced current is in a direction that tends to slow the moving bar – it will take an external force to keep it moving. 29-3 EMF Induced in a Moving Conductor

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2 The induced emf has magnitude 29-3 EMF Induced in a Moving Conductor This equation is valid as long as B , l , and v are mutually perpendicular (if not, it is true for their perpendicular components). Example 29-6: Does a moving airplane develop a large emf? An airplane travels 1000 km/h in a region where the Earth’s magnetic field is about 5 x 10 -5 T and is nearly vertical. What is the potential difference induced between the wing tips that are 70 m apart? 29-3 EMF Induced in a Moving Conductor Example 29-7: Electromagnetic blood-flow measurement. The rate of blood flow in our body’s vessels can be measured using the apparatus shown, since blood contains charged ions. Suppose that the blood vessel is 2.0 mm in diameter, the magnetic field is 0.080 T, and the measured emf is 0.10 mV. What is the flow velocity of the blood?
3 29-3 EMF Induced in a Moving Conductor Example 29-8: Force on the rod. To make the rod move to the right at speed v , you need to apply an external force on the rod to the right. (a) Explain and determine the magnitude of the required force. (b) What external power is needed to move the rod? A generator is the opposite of a motor – it transforms mechanical energy into electrical energy. This is an ac generator: The axle is rotated by an external force such as falling water or steam. The brushes are in constant electrical contact with the slip rings. 29-4 Electric Generators

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4 29-4 Electric Generators If the loop is rotating with constant angular velocity ω , the induced emf is sinusoidal: For a coil of N loops, Example 29-9: An ac generator.
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PY208N-Lecture-21 - Physics 208N-004 Lecture#21 4 March...

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