PHYS 221L Midterm, Fall 2011

Physics 221L – Mid-term December 2011 1.   You wish to design an instrument to measure magnetic fields using the circular path of electrons in the field; the device is to have dimensions no greater than 5 cm - using accelerating potentials from 20 to 200V. Please explain how you would build it. What is the smallest field you can measure? Assuming you use a travelling microscope to measure the diameter of the path with an uncertainty of 0.05 mm, what is the uncertainty of your instrument? 2.   In your spectroscopy experiment, you use a grating with 500 lines per mm; the source is a hydrogen lamp. You obtain the following data in degrees with an uncertainty of 0.3 degrees on all values: Color                         Right left Red                           350.2                           312.3 Cyan                         345.2 317.4 Blue                          343.7 318.6 Red                           12.4                          290.8 Cyan                         0.7                            303.0 Blue                          356.2                         306.1 Use your data to find the Rydberg constant