How to calculate the work done by the external force overcoming

1. UAB = - 1000V
the work done by the electric field force is the positive work done by the electric field force, and the work done by overcoming the electric field force is the negative work done by the electric field force
in fact, it is very simple to substitute u, W and Q with positive and negative signs into the calculation
for example, WAB = - 1000j, q = + 1C
UAB = WAB / Q = - 1000j / 1C = - 1000V
note that ab cannot be replaced by ba
if the charge is negative, replace Q with - 1C, If the calculated potential is positive, then a is higher than B. if it is negative, then B is higher than a

2. Just remember the conservation of energy. When the external force works in the magnetic field, part of it generates electric current and heat. Part of it becomes kinetic energy, if any

3. If your answer is quoted from other places, please indicate the source

4. If the external force overcomes the electric field force, it means that the external force does positive work and the electric field force does negative work, then the electric potential energy increases. Since the electric potential energy has increased, it is moving from the place with small electric potential energy to the place with large electric potential energy

5. A. The electric field force of positive charge is the same as the direction of electric field strength. If it moves along the direction of electric field line, the electric field force must do positive work, so a is wrong.
B. if the external force overcomes the electric field force to do work, it only means that the electric field force does negative work, but the work of the electric field force is only related to the initial and final position of the charge, and has nothing to do with the path, so the positive charge does not necessarily move against the direction of electric field line If the electric field force does negative work, the electric potential energy of the charge will certainly increase, so C is correct and D is wrong.
select C

6. This kind of problem can be compared with the work done by gravity
when an object moves from low to high, the direction of motion is upward and the gravity is downward. At this time, we say that gravity does negative work and the potential energy of gravity increases. The reason why we say that we do negative work is because the direction of force and the direction of motion are opposite. There is another way to say that external force overcomes gravity to do work. This is because to raise an object, it is necessary to have an external force to overcome downward gravity
from high to low, the object moves in the same direction as gravity, gravity does positive work, and the gravitational potential energy decreases
look at this question
1
2. The electric potential energy increases
3. If the potential at infinity is zero, then the potential energy of the positive charge at infinity is zero. From infinity to point a, the increase of electric potential energy is equal to the work done by the external force to overcome the electric field force. 0 + W = WA, so the potential energy Wa of the positive charge at point a is 2x10 ^ (- 2) J
potential φ A=WA/q=2X10^(-2)/2X10^(-4)=100V

7. Let me tell you an algorithm of using electric field force to move charge to do work:
if charge q is from a to B, electric field force does work on charge WAB, AB potential difference is UAB, then WAB = Q * UAB,
back to the problem, In the whole process (a to c), the total work done by the electric field force is WAB + WBC = (+ x) + (- x1)
so x-x1 = Q * UAC
the electric potential difference of AC is UAC = (x-x1) / Q
note: in the above algorithm, each quantity contains sign calculation. When the external force overcomes the electric field force to do work x1, it means that the electric field force does negative work X1 to the charge.

8. A. The electric field force of positive charge is the same as the direction of electric field strength. If it moves along the direction of electric field line, the electric field force must do positive work, so a is wrong. < br > B. if the external force overcomes the electric field force to do work, it only means that the electric field force does negative work, but the work of the electric field force is only related to the initial and final position of the charge, and has nothing to do with the path, so the positive charge does not necessarily move against the direction of electric field line If the electric field force does negative work, the electric potential energy of the charge will certainly increase, so C is correct and D is wrong. < br > select C

9. If the external force overcomes the electric field force, it means that if the external force does positive work and the electric field force does negative work, then the electric potential energy will increase. Since the electric potential energy increases, then it will move from the place where the electric potential energy is small to the place where the electric potential energy is large

10. AB, the work done by the external force to overcome the electric field force only means that the electric field force does negative work, and the change of kinetic energy is related to the work done by the external force. Only knowing the negative work done by the electric field force can not determine the work done by other forces on the charge, so it is impossible to judge whether the kinetic energy increases or decreases, so AB is wrong< When the electric field force does negative work, the electric potential energy of the charge increases, so the electric potential energy of the initial position of the charge is less than that of the end position. Because the electric field force does work independent of the path, it can only indicate that the charge may move from the point where the electric potential energy is less than to the point where the electric potential energy is greater (or it may pass through the point where the electric potential energy is greater in the midway), so C is wrong and D is correct. < br > select D