• anonymous
Find the potential difference ΔVe required to stop an electron (called a "stopping potential") moving with an initial speed of 1.96 107 m/s.
  • Stacey Warren - Expert
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  • katieb
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  • anonymous
We need to know the charge and mass of an electron. I'll assume you have these values handy (let me know otherwise and I can look them up). Volts have units of \[\rm joules \over coulombs\]If work also have units of joules. We can use the work-energy theorem, which states\[W = \Delta KE + \Delta PE\] we will assume there is no change in potential energy, therefore\[W = \Delta KE = {1 \over 2} m (v_f-v_i)\] This being said, let's observe that\[V = {(1/2) m (v_f-v_i) \over q}\]where q is the charge of an electron (in coulombs).

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