Physics 262 Spring 2018 Exam 1 16) If the electric potential at a point in space
ID: 1874953 • Letter: P
Question
Physics 262 Spring 2018 Exam 1 16) If the electric potential at a point in space is zero, then the electric field at that point must also be Version: E zero. A) True B) False 17) A charge Q is uniformly spread over one surface of a very large nonconducting square elastic sheet having sides of length d. At a point P that is 1.25 cm outside the sheet, the magnitude of the electric field due to the sheet is E. If the sheet is now stretched so that its sides have length 2d, what is the magnitude of the electric field at P? A) E/2 B) E/4 9 E D) 2E E) 4E 18) Suppose a region of space has a uniform electric field, directed towards the right, as shown in the figure. Which statement about the electric potential is true? A) The potential at points A and B are equal, and the potential at point C is higher than the potential at point A. B) The potential at points A and B are equal, and the potential at point C is lower than the potential at point A. C) The potential at all three locations (A, B, C) is the same because the field is uniform. D) The potential at point A is the highest, the potential at point B is the second highest, and the potential at point C is the lowest 19) Suppose you have two point charges of opposite sign. As you move them farther and farther apart, the potential energy of this system relative to infinity A) stays the same. B) increases. Q) decreases. 20) A positive point charge O is fixed on a very large horizontal frictionless tabletop. A second positive point charge q is released from rest near the stationary charge and is free to move. Which statement best describes the motion ofq after it is released? A) Its acceleration is zero just after it is released B) Its speed will be greatest just after it is released. CAs it moves farther and farther from Q, its speed will decreas. D) As it moves farther and farther from Q, its acceleration will keep increasing. E) As it moves farther and farther from Q, its speed will keep increasing.Explanation / Answer
(16)
Electric field is the gradient of the potential at a point. So, you can't determine the field from the potential at a point. Even though zero potential exist, there may be non zero electric field.
Given statement is Flase
(17) As it is square plate, the area has increased from L² to (2L)² = 4L², implies that area is 4 times bigger. The surface charge density is therefore 1/4 times. As the electric field is proportional to the surface charge density, the field becomes E/4.
correct option ( B).
(18) If you placed positive charges anywhere in the diagram, they will move to the right. Potential is work done to move the charge in the direction of field. In this case,meaning that the voltage is lower to the right. The potential at points A and B are equal and the potential at point C is lower than the potential at point A.
correct option ( B).
(19) The potential energy Increases. As they have same sign of charge, they attract each other, In order to move farther, we have to do more work, implies that the potential energy increases.
correct option ( B).
(20)
As they move farther due to repulsion, the force decreases and hence the acceleration changes at greater scale. So, the speed of the charge greater as they move far apart. As it moves farther and farther from +Q, its speed will keep increasing.
correct option ( E ).