AAMC Qpack C/P #25

[663697]

The question asked how the final kinetic energy compares to the initial potential energy of the electron immediately before being ejected. By conservation of energy I said that PE(initial) = KE(final) and this was the answer. However, it also states there is 50 V of potential difference between the cathode and anode which will cause the electron to gain 50 eV of energy. Would this be in the form of potential energy? I'm not understanding how this fits into the conservation of energy principle since it states this 50 eV will be on top of the kinetic energy it gains.

---

Members don't see this ad.

 

[aldol16]

That 50 V of potential difference between the electrodes is what gives rise to the initial potential energy of the electron. To more concretely visualize this, we might use an analogy. A ball at the top of a hill has potential energy. That potential energy arises from the height difference between the top of the hill and the ground. Once you roll the ball down the hill, all that potential energy will have been converted to kinetic energy. In this analogy, the potential energy of the ball is like the potential energy of the electron. The height of the hill is like the potential difference across the electrodes.

 

[LnSin]

Yeah so the 50 eV is initially a potential. It's like if you have a hose and you don't turn the water on. Then you pinch one end and turn on the Water. When it builds up you get potential energy--that's just what voltage is. Finally, when you release that block, the water shoots out and the energy is converted to kinetic.

The water analogies really help by the way. E.g. Current is flow rate, pressure is voltage, resistance is like a sponge etc.


Sent from my iPhone using Tapatalk