A solenoid is a series of loops of wire, one after another, to make a long tube. A long solenoid wound with fine wire carrying a current would generate a nearly uniform magnetic field inside the solenoid, and these devices are widely used for that purpose. They are also a basis of relays and actuators that can create mechanical motion from the interaction of this field with a material. You'll find a simple formula for the field inside a solenoid on the class website where it is derived from Ampere's law. Suppose we want to create a field inside the solenoid that is the same as Earth's magnetic field, typically arouns 50×10-6 T or 50 micro-tesla. We might do this to cancel Earth's field in a sensitive experiment for example. We build a solenoid with fine wire wrapped on a tube, and there are 1000 turns per meter of this wire. That is each loop of wire takes 1 mm along the coil. We connect the ends of the wire to a voltage source we can control such that current flows through the wire. Which of these is closest to the current you calculate that would create a magnetic field equal to Earth's field inside the solenoid? 40 amperes less than a microampere more than 100 amperes 40 milliamperes 40 microamperes
A solenoid is a series of loops of wire, one after another, to make a long tube. A long solenoid wound with fine wire carrying a current would generate a nearly uniform magnetic field inside the solenoid, and these devices are widely used for that purpose. They are also a basis of relays and actuators that can create mechanical motion from the interaction of this field with a material. You'll find a simple formula for the field inside a solenoid on the class website where it is derived from Ampere's law.
Suppose we want to create a field inside the solenoid that is the same as Earth's magnetic field, typically arouns 50×10-6 T or 50 micro-tesla. We might do this to cancel Earth's field in a sensitive experiment for example. We build a solenoid with fine wire wrapped on a tube, and there are 1000 turns per meter of this wire. That is each loop of wire takes 1 mm along the coil. We connect the ends of the wire to a voltage source we can control such that current flows through the wire.
Which of these is closest to the current you calculate that would create a magnetic field equal to Earth's field inside the solenoid?
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40 amperes |
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less than a microampere |
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more than 100 amperes |
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40 milliamperes |
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40 microamperes |
The magnetic field produced by a solenoid is given by the equation
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