3B SCIENTIFIC PHYSICS 1 2 3 4 5

3B SCIENTIFIC PHYSICSElectron-Beam Deflection Tube D 1000651Instruction sheet10/15 ALF71 Fluorescent screen2 Lower deflection plate3 Boss with 4-mm plug forconnecting deflection plates4 Electron gun5 4-mm sockets for connectingheater supply and cathode6 4-mm plug for connectinganode7 Upper deflection plate62110 9 8 7 6 5 4 3 2123-1 2451. Safety instructions2. DescriptionHot cathode tubes are thin-walled, highly evacuated glass tubes. Treat them carefully as thereis a risk of implosion. Do not subject the tube to mechanical stresses. Do not subject the connection leads to anytension. The tube may only be used with tube holderD (1008507).If voltage or current is too high or the cathode isat the wrong temperature, it can lead to the tubebecoming destroyed. Do not exceed the stated operating parameters. Only change circuit with power supplyequipment switched off. Only exchange tubes with power supplyequipment switched off.When the tube is in operation, the stock of thetube may get hot. If necessary, allow the tube to cool beforedismantling.The compliance with the EC directive on electromagnetic compatibility is only guaranteedwhen using the recommended power supplies.The electron-beam deflection tube is intendedfor investigating the deflection of electron beamsin electrical and magnetic fields. It can be usedto estimate the specific charge of an electrone/m and to determine the electron velocity v.The electron-beam deflection tube comprises anelectron gun which emits a narrow, focussedribbon of cathode rays within an evacuated,clear glass bulb. A tungsten 'hairpin' filament hotcathode is heated directly and the anode takesthe form of a cylinder. The deflection of rays canbe achieved electrostatically by means of a builtin plate capacitor formed by the pair of deflection plates or magnetically with the help of theHelmholtz coils D (1000644) magnetically. Thecathode rays are intercepted by a flat micasheet, one side of which is coated with a fluorescent screen and the other side of which isprinted with a centimetre graticule so that thepath of the electrons can be easily traced. Themica sheet is held at 15 to the axis of the tubeby the two deflecting plates.1

Insert the Helmholtz tubes into the holes ofthe tube holder. Turn on the high-tension power supply. Energise the Helmholtz coils and observethe path of the beam.The path of the luminous beam is circular, thedeflection being in a plane perpendicular to theelectromagnetic field.At fixed anode voltage the radius decreases withincreasing coil current.With a fixed coil current the radius increaseswith increasing anode potential, indicating ahigher velocity.An electron of mass m and charge e movingperpendicular to a uniform magnetic field B atvelocity v is deflected by the Lorentz force Bevonto a circular path of radius r.3. Technical dataFilament voltage:Anode voltage:Anode current:Deflector platevoltage:Distance betweenplates:Fluorescent screen:Glass bulb:Total length: 7,5 V AC/DC1000 V – 5000 V DC0.1 mA approx. at 4000 V5000 V max.54 mm approx.90 mm x 60 mm130 mm Ø approx.260 mm approx.4. OperationTo perform experiments using the electronbeam deflection tube, the following equipment isalso required:1 Tube holder D10085072 High voltage power supply 5 kV (115 V, 50/60 Hz)1003309or2 High voltage power supply 5 kV (230 V, 50/60 Hz)10033101 Helmholtz pair of coils D10006441 DC power supply 20 V (115 V, 50/60 Hz)1003311or1 DC power supply 20 V (230 V, 50/60 Hz)10033121 Analogue multimeter AM511003074Additionally recommended:Protective Adapter, 2-PoleB e v m v2r(1)5.2 Electric deflection Set up the tube as in fig 3. Connect the minus-pole of the anode voltage to the 4-mmsocket marked with a minus. Turn on the high-tension power supply. Switch on the deflector plate voltage andobserve the path of the beam.An electron with velocity v passing through theelectric field E produced by a plate capacitorheld at a voltage UP with a plate spacing d isdeflected into the curved path of a parabolagoverned by the equation:1 e E 2(2) x2 m v2where y is the linear deflection achieved over alinear distance x.y 10099614.1 Setting up the tube in the tube holder The tube should not be mounted or removedunless all power supplies are disconnected. Push the jaw clamp sliders on the stanchionof the tube holder right back so that the jawsopen. Push the bosses of the tube into the jaws. Push the jaw clamps forward on the stanchions to secure the tube within the jaws. If necessary plug the protective adapter ontothe connector sockets for the tube.5.3 Calculating e/m und v5.3.1 By means of magnetic deflection Set up the experiment as in Fig 2.The velocity is dependent on the anode voltageUA such that:e UA(3)mSolving equations 1 and 3 simultaneous givesthe following expression for the specific chargee/m:v 2 4.2 Removing the tube from the tube holder To remove the tube, push the jaw clampsright back again and take the tube out of thejaws.e2 UA m B r 2(4)UA can be measured directly, B and r can bedetermined experimentally.5. Example experiments5.1 Magnetic deflection Set up the tube as in Fig. 2. Connect theminus-pole of the anode voltage to the 4mm socket marked with a minus.5.3.1.1 Determining rThe radius of curvature r is obtained geometrically as in Fig. 1:2

r 2 x 2 r y 25.3.3 By means of field compensation Set up the experiment as in Fig 4. Turn on the high-tension power supply unitsand deflect the beam electrically. Energise the Helmholtz coils and adjust thevoltage in such a way that the magnetic fieldcompensates the electric field and the beamis no longer deflected.The magnetic field compensates the deflectionof the electron beam caused by the electric field:so that:r x2 y 22 y(5)5.3.1.2 Calculating BThe magnetic flux B of a magnetic field generated by the Helmholtz coils in Helmholtz geometryand the coil current I can be calculated:e E e v BThe velocity v can be calculated:3 4 2 μ n(6)B 0 I k IR 5 where k in good approximation 4,2 mT/Awith n 320 (windings) and R 68 mm (coilradius).v (8)UP. For the calculation of B refer todpoint 5.3.1.2.The specific charge e/m can be calculated:where E 5.3.2 By means of electric deflection Set up the experiment as in Fig 3.e/m can be calculated from equation 2:e 2y v 2 m E x2EB2e1 E m 2 UA B (7UPdwith UP deflector plate voltage and d platespacing.where E MryPxFig. 1 Determining r3(9)

DC POWER SUPPLY 0 . 5 kVUH1IA23450AKV0 . 5 kVZUPUF2110 9 8 7 6 5 4 3 212-AZFig. 2 Magnetic deflectionDC POWER SUPPLY 0 . 5 kV123DC POWER SUPPLY 0 . 5 kV415023450KVKV0 . 5 kV0 . 5 kVUPUPFig.3 Electric deflection4UF-2110 9 8 7 6 5 4 3 212

IAUHADC POWER SUPPLY 0 . 5 kV123450KVZ0 . 5 kVDC POWER SUPPLY 0 . 5 kV123UA450KV0 . 5 kV2110 9 8 7 6 5 4 3 212UF-UPAZFig. 4 Calculating e/m by means of field compensation3B Scientific GmbH Rudorffweg 8 21031 Hamburg Germany www.3bscientific.comTechnical amendments are possible Copyright 2015 3B Scientific GmbH

The electron-beam deflection tube is intended for investigating the deflection of electron beams in electrical and magnetic fields. It can be used to estimate the specific charge of an electron e/m and to determine the electron velocity v. The electron-beam deflection tube comprises an