Scalar Quantity - General Physics - Solved Past Paper, Exams of Physics

Download Scalar Quantity - General Physics - Solved Past Paper and more Exams Physics in PDF only on Docsity! 7. (25 pts) a) (5 pts) If there are a bunch of charges in some region of space and you want to compute the electric potential, do you need to use vector addition? Explain. Since electric potential is a scalar quantity, when summing the contributions to the total potential from each of the charges you do not need to use vector addition. b) (5 pts) Electric fields point in the direction of decreasing electric potential. Why then, when an electron is moved in the direction opposite the electric field, does its electric potential energy decrease? While the electric potential is increasing, the electron has a negative charge. Thus the electric potential energy decreases. c) (5 pts) Einstein demonstrated that the intensity of a beam of light is related to the number of photos in the beam rather than to the energy of the individual photons. What property of the photon is related to the amount of energy it is carrying? The property of the photon related to the amount of energy it is carrying is color. Blue photons carry more energy than red photons. The photoelectric effect shows this quite nicely in that electrons are kicked off of the metal immidiately even with the dimmest light but only for light that is “above” a certain color (i.e. has enough energy). d) (5 pts) Is it possible for an electrical circuit to induce an electric potential in itself? Explain your reasoning. This is possible and is called self-inductance. The circuit creates a magnetic field that passed through the circuit itself and, if changing (due to a changing current), induces a potential in the circuit. This “back-emf” is very important in many modern electrical devices such as electric motors. Without back- emf, an electric motor would almost appear to be a dead-short and would blow out the fuse or circuit breaker every time it was turned on. e) (5 pts) Relativity implies that photons have no mass. Is it then possible for photons, and hence light, to transfer momentum? Yes, photons can transfer momentum. This is the effect that allows light to exert force on objects.