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Electron Beam Deflection

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Electron Beam Deflection


1. **State the problem:** We have an electron beam with velocity $v = 7.15 \times 10^7$ m/s passing through an electric field created by a voltage $U = 1440$ volts across a distance $D = 100$ cm (1 m). The beam is deflected by $y_0 = 0.62$ cm after traveling a length $L = 10$ cm in the field. We want to analyze the forces and trajectory of the electron beam. 2. **Convert units:** - $D = 100$ cm = 1 m - $L = 10$ cm = 0.1 m - $y_0 = 0.62$ cm = 0.0062 m 3. **Calculate the electric field $E$ between the plates:** $$E = \frac{U}{D} = \frac{1440}{1} = 1440 \text{ V/m}$$ 4. **Calculate the force $F$ on the electron due to the electric field:** The electron charge is $e = 1.6 \times 10^{-19}$ C. $$F = eE = 1.6 \times 10^{-19} \times 1440 = 2.304 \times 10^{-16} \text{ N}$$ 5. **Calculate the acceleration $a$ of the electron in the direction of the electric field:** Electron mass $m = 9.11 \times 10^{-31}$ kg. $$a = \frac{F}{m} = \frac{2.304 \times 10^{-16}}{9.11 \times 10^{-31}} = 2.53 \times 10^{14} \text{ m/s}^2$$ 6. **Calculate the time $t$ the electron spends in the electric field region:** $$t = \frac{L}{v} = \frac{0.1}{7.15 \times 10^7} = 1.4 \times 10^{-9} \text{ s}$$ 7. **Calculate the vertical velocity component $v_y$ gained due to acceleration:** $$v_y = a t = 2.53 \times 10^{14} \times 1.4 \times 10^{-9} = 3.54 \times 10^5 \text{ m/s}$$ 8. **Calculate the vertical displacement $y$ inside the plates:** Using $y = \frac{1}{2} a t^2$, $$y = 0.5 \times 2.53 \times 10^{14} \times (1.4 \times 10^{-9})^2 = 0.025 \text{ m} = 2.5 \text{ cm}$$ 9. **Calculate the total deflection $y_0$ after the plates:** After leaving the plates, the electron travels with vertical velocity $v_y$ for a distance $d = 4$ cm = 0.04 m. Time to travel this distance: $$t_2 = \frac{d}{v} = \frac{0.04}{7.15 \times 10^7} = 5.6 \times 10^{-10} \text{ s}$$ Vertical displacement after plates: $$y_2 = v_y t_2 = 3.54 \times 10^5 \times 5.6 \times 10^{-10} = 0.0002 \text{ m} = 0.02 \text{ cm}$$ 10. **Total vertical deflection:** $$y_\text{total} = y + y_2 = 2.5 + 0.02 = 2.52 \text{ cm}$$ **Note:** The given $y_0 = 0.62$ cm is smaller than calculated, which may indicate experimental conditions or approximations. **Final answer:** The electron beam experiences a vertical deflection of approximately $2.52$ cm due to the electric field.