C- PHYS102 - LAB 3 - eOver-M-Final

At x 0 eq7 can be reduced to bx x o ni 4 r

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Unformatted text preview: ssed as: Bx ( x ) = # µo NIR 2 ! 1 1 ' & + 2 & !( x + R / 2)2 + R 2 # 3/2 !( x % R / 2)2 + R 2 # 3/2 ' $ " $$ "" [7] where µo = 4π x 10 ­7 Tm/A is the permeability of free space, N is the number of turns in each of the pair of coils (N = 130 in this apparatus), I is the coil current and R is the radius of the coil. At x = 0, eq.[7] can be reduced to: Bx ( x ) = µo NI ! 4 $ R #5& "% 3/2 = 1.168 ' 10 (4 I / R [8] 3. Experimental 3.1 The e/m Apparatus Figure 3.On the left, the e/m apparatus consisting of a pair of Helmholtz coils, vacuum tube and control box containing power supplies for the tube heater, coils and accelerating voltage. On the right, shown schematically, the electron gun consisting of a heated cathode, protective metal grid, anode and power source to the accelerating voltage. The e/m apparatus, depicted in Figure 3, consists of a partially evacuated glass bulb placed between the Helmholtz coils. Inside the glass bulb, electrons are emitted from a heated cathode connected to the negative terminal of a high ­voltage power supply. The cathode is partially shielded by a surrounding grid that allows electrons to pass through. The electrons are then attracted to an anode mounted below the grid and connected to the positive terminal of the high ­voltage power supply. The electrons escaping through the grid are accelerated downwards towards the anode by an adjustable potential, V. The accelerated electrons emerge from the electron gun with a velocity v and enter a region of uniform magnetic field B. Because the electrons’ velocity is transverse to the B ­field direction, the beam is deflected by the Lorentz force F = ev x B r...
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