Magnetic Force on a Moving Charge
Lab V, Problem 8: Magnetic Force on a Moving Charge
John Greavu
Partners: Hannah Eshenaur and David Sturg
August 15, 2013
Physics 1302W, Professor: John Capriotti, TA: Barun Dhar
Objective In order to improve the design of an electron microscope, we attempted to use a magnetic field to control the electron beam. Utilizing a cathode cay tube (CRT), we oriented a magnetic field perpendicular to the axis of the CRT’s electron beam. From previous experience, we decided on using Helmholtz coils to produce a reasonably uniform magnetic field. We measured the deflection of an electron, (our dependent, “response”, variable), as a function of the magnitude of the magnetic field, , and the electron’s velocity, (our independent, “control”, variables).
Prediction and Procedure
For this experiment, we used the CRT, a digital multimeter (DMM), compass, meter stick, 200-turn (each) Helmholtz coils, a Hall probe to measure the magnetic field (and accompanying computer data acquisition system), and banana cables to make the appropriate connections.
Figure 1, the experimental set up:
To create a uniform magnetic field, the Helmholtz coils were positioned as shown above in Figure 1 and their electrical currents were tested to be equal in addition to flowing in the same direction.
The Hall probe was then used to measure the magnetic field. It was placed in the approximate center of the coils (with no current flowing through them yet) perpendicular to the planes of the coils (and in the same direction in which the electron beam was to be shot) and calibrated. The ambient magnetic field reading (due to Earth’s magnetic field/the field due to nearby electronics) given by the probe/data-acquiring software was noted at 0.54 gauss. The probe/software was then zeroed.
The CRT was properly connected to a power supply and turned on. The voltage of the accelerating plates was set to 500 volts. Test deflections were done to align the y-axis with the vertical
John Greavu
Partners: Hannah Eshenaur and David Sturg
August 15, 2013
Physics 1302W, Professor: John Capriotti, TA: Barun Dhar
Objective In order to improve the design of an electron microscope, we attempted to use a magnetic field to control the electron beam. Utilizing a cathode cay tube (CRT), we oriented a magnetic field perpendicular to the axis of the CRT’s electron beam. From previous experience, we decided on using Helmholtz coils to produce a reasonably uniform magnetic field. We measured the deflection of an electron, (our dependent, “response”, variable), as a function of the magnitude of the magnetic field, , and the electron’s velocity, (our independent, “control”, variables).
Prediction and Procedure
For this experiment, we used the CRT, a digital multimeter (DMM), compass, meter stick, 200-turn (each) Helmholtz coils, a Hall probe to measure the magnetic field (and accompanying computer data acquisition system), and banana cables to make the appropriate connections.
Figure 1, the experimental set up:
To create a uniform magnetic field, the Helmholtz coils were positioned as shown above in Figure 1 and their electrical currents were tested to be equal in addition to flowing in the same direction.
The Hall probe was then used to measure the magnetic field. It was placed in the approximate center of the coils (with no current flowing through them yet) perpendicular to the planes of the coils (and in the same direction in which the electron beam was to be shot) and calibrated. The ambient magnetic field reading (due to Earth’s magnetic field/the field due to nearby electronics) given by the probe/data-acquiring software was noted at 0.54 gauss. The probe/software was then zeroed.
The CRT was properly connected to a power supply and turned on. The voltage of the accelerating plates was set to 500 volts. Test deflections were done to align the y-axis with the vertical