LECTURE DEMONSTRATION MANUAL | Instructional Research Lab : ucla physics | |
main page | Simple Measurement of B |
table of contents | |
search |
E.3.5 Simple Measurement of B An undamped compass needle vibrates about equilibrium in a B-field; the vibration frequency can be used as a measure of B. Let the (unknown) moment of inertia of the compass needle be I, and its (unknown) magnetic moment μ. Then the restoring torque τ=Bµsinθ. Using the analogy to linear harmonic motion the angular frequency of vibration is ω = √ (k/m) = √ (Bµ/I) Thus, the frequency of vibration of the needle is proportional to √B. Measure the frequency of vibration of the compass needle in the Earth's field of 0.5 gauss, and obtain the strength of other B-fields from these results. Gauss Meter Accurate and detailed measurements of B-field can be made with a Gaussmeter and Hall probe. You can illustrate the size of the gauss unit and the strength of various magnets, or make measurements of B-fields for electron deflection, etc. |