Potential and potential energy relationship and units. (For more on the units of V, J, and eV, see the text's discussion in section 22.1, just before example 22.1, or my video!) (a) A -50µC charge moves along a straight line a distance of 20 cm in a uniform electric field of 120 N/C. The charge is traveling at an angle of 30 degrees relative to the direction of the electric field. How much electrical energy (in Joules) did the charge gain or lose? And is it a gain or loss? Convert the energy to units of eV. (b) The potential difference between the two terminals of a AA battery is 1.5 V. An electron moving from the negative to the positive terminal will lose electric potential energy (and, presumably, gain some other energy or transfer it to elsewhere.) How do we know the electrical potential energy of the electron decreases in this case? How much potential energy energy does one electron lose when it moves from the negative terminal to the positive one of this battery? Answer first in eV and then in Joules. (c) An electron moves a distance of 20 cm. The start location is at a potential that is 120 V lower than the potential at the ending location. Find the change in the electron's potential energy in units of eV first and then convert the answer to units of Joules. (d) When is it easier to calculate the energy in eV and then convert to Joules if necessary? When is it easier to calculate the energy in Joules first and then convert to eV if necessary? (e) For E level work: If the electric potential energy of an electron moving to a higher potential is converted to light (a photon is emitted,) then the wavelength of the light is related to the change in the electron's energy U by the following relationship: X = (1240 nm eV)/U, where the energy is measured in eV. Use this relationship find the wavelength (in nm) of the light emitted by the electron crossing a 1.5 V potential difference. In what part of the spectrum (radio, IR, visible, and if so, what color UV, x ray, etc) is that? (you probably need to look it up! Feel free to search the internet.)