AAMC 4 Question 42

[kabtq9s]

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Guys I'm having trouble understanding the logic behind this question, any comments are appreciated

http://mysowar.files.wordpress.com/2011/05/42.png

someone already asked about it but no one answered him

 

[Rabolisk]

An electron is negatively charged, so it will accelerate from the negatively charged cathode to the positively charged anode. From energy standpoint, this is equivalent to the electron's potential energy being converted to the kinetic energy. If the energy of the photon that is used to eject the electron is only slightly larger than the electron's work function, then the electron has very little kinetic energy. In other words, its initial kinetic energy is approximately 0. When the electron reaches the anode, approximately all of its final kinetic energy is from the initial potential energy. Hence they are equal.

 

[Amrazzz]

Guys I'm having trouble understanding the logic behind this question, any comments are appreciated

http://mysowar.files.wordpress.com/2011/05/42.png

someone already asked about it but no one answered him

You can use conservation of energy find that. So lets say the capacitor has 2 different plates, one has a negative charge and the other has an equal positive charge. When an electron is near the negative plate, it's potential energy is the greatest - since both are negative, they will tend to repel each other towards the positive plate. As the electron reaches the positive plate, it will lose its potential energy, while gaining an equal amount of kinetic energy. Since + and - charges attract, theres only a force of attraction between them.

You can also think about it this way: think of a negative charge as a balloon, it likes to "Float" towards greater potential (+) and a positive charge as a rock since it wants to "drop" to lower potential (-)

 

[kabtq9s]

thanks guys, this was actually an easy question but the question wording made it unclear for me at first