current balance

# current balance - Laboratory Report PHYS 122L The Current...

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Laboratory Report PHYS 122L The Current Balance: A Measurement of μ o Purpose of the Experiment: To use a current balance to measure the permeability of free space, μ o . To compute the expected speed of light in a vacuum, using the measured value of μ o and the known value of the permittivity of free space, ε o . To determine the direction of the component of Earth’s magnetic field through the classroom. Experimental Procedure: The power supply is connected to the current balance using the double-pole-double-throw switch so that the polarity can easily be switched. The base of the current balance is leveled and the two wire bars are aligned to make them as parallel as possible, when viewed from the top and the side. The counterweight on the balance is adjusted until the separation between the wires is about 1 mm. The laser and screen are set up so that the laser reflects off of the mirror and hits the screen. The value at which the laser hits the screen is recorded at X d,o . Mass is placed on the pan so that the wires touch. The new position of the laser beam on the screen is recorded as X contact . This is repeated four more times so that we have five values of X d,o and X contact . The distance from the mirror to the screen, D screen , from the mirror to the wires, D wires , and the length of the wire bars, L, are measured along with their uncertainties. The mass is removed from the pan and the laser beam is allowed to return to its original, X d,o , position. The 10 mg mass is placed on the pan and the power supply is turned on. The current is adjusted until the laser returns to X d,o . The value of the current and the mass used are recorded. The switch is then flipped and the current is adjusted until the spot again returns to X d,o and record the value. This is repeated in 10 mg increments until the

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current balance - Laboratory Report PHYS 122L The Current...

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