Magnetic Field and Cathode Ray Tube
Experiment 4 Measurement of e by Thomson's bar magnet method. m
Apparatus: Cathode ray tube (CRT) with power supply unit, one pair of bar magnets, high resistance voltmeter, magnetometer, stopwatch. Purpose of experiment: e To measure the specific charge, i.e. charge to mass ratio , of an electron using m Thomson's bar magnet method. Basic methodology: Electrons in a CRT are deflected in the vertical direction by applying a potential between the vertical deflection plates of the CRT. A magnetic field perpendicular to the deflecting electric field is produced using a pair of bar magnets. The position of the magnets is adjusted so as to cancel the deflection of the electrons. The knowledge of the deflecting potential and the magnet field of the bar magnets leads to a calculation of the specific charge. I. Introduction We have learnt that the electron has a negative charge whose magnitude e equals 1.6 × 10−19 Coulomb and mass (m) equal to 9.1 × 10 −31 Kg. Millikan's Oil Drop method enables us to measure the electron charge but the mass of the electron can not be measured directly. It is calculated by measuring the value of e/m. The aim of this experiment is to determine value of e/m by Thomson's method. This involves the motion of an electron in a cathode ray tube (CRT). A simplified form of a cathode ray tube is shown in Fig.1. The electrons are emitted from the cathode and accelerated towards the anode by an electric field. A hole in the accelerating anode allows the electrons to pass out of the electron gun and between the two sets of deflection plates. The metallic coating inside the tube shields the right end free of external electric fields and conducts away the electrons after they strike the fluorescent screen where they form a luminous spot. Plates for Plates for vertical Focusing Anode horizontal deflection Accelerating deflection Anode Control Grid Electron Beam Metallic Coating Fluorescent Screen
Heater Cathode Electron Gun Fig. 1
I.2
Apparatus: Cathode ray tube (CRT) with power supply unit, one pair of bar magnets, high resistance voltmeter, magnetometer, stopwatch. Purpose of experiment: e To measure the specific charge, i.e. charge to mass ratio , of an electron using m Thomson's bar magnet method. Basic methodology: Electrons in a CRT are deflected in the vertical direction by applying a potential between the vertical deflection plates of the CRT. A magnetic field perpendicular to the deflecting electric field is produced using a pair of bar magnets. The position of the magnets is adjusted so as to cancel the deflection of the electrons. The knowledge of the deflecting potential and the magnet field of the bar magnets leads to a calculation of the specific charge. I. Introduction We have learnt that the electron has a negative charge whose magnitude e equals 1.6 × 10−19 Coulomb and mass (m) equal to 9.1 × 10 −31 Kg. Millikan's Oil Drop method enables us to measure the electron charge but the mass of the electron can not be measured directly. It is calculated by measuring the value of e/m. The aim of this experiment is to determine value of e/m by Thomson's method. This involves the motion of an electron in a cathode ray tube (CRT). A simplified form of a cathode ray tube is shown in Fig.1. The electrons are emitted from the cathode and accelerated towards the anode by an electric field. A hole in the accelerating anode allows the electrons to pass out of the electron gun and between the two sets of deflection plates. The metallic coating inside the tube shields the right end free of external electric fields and conducts away the electrons after they strike the fluorescent screen where they form a luminous spot. Plates for Plates for vertical Focusing Anode horizontal deflection Accelerating deflection Anode Control Grid Electron Beam Metallic Coating Fluorescent Screen
Heater Cathode Electron Gun Fig. 1
I.2