The electric field strength at a point may be defined as?

Question

A. the force exerted on unit positive charge placed at that point.
B. the force per unit positive charge on a small test charge placed at that point.
C. the work done on unit positive charge to move the charge to that point from infinity.
D. the work done per unit positive charge to move a small test charge to that point from infinity.

Answer 1

B.

Evidence:
In physics, the space surrounding an electric charge has a property called an electric field. This electric field exerts a force on other charged objects. The concept of electric field was introduced by Michael Faraday.

The electric field is a vector with SI units of newtons per coulomb (N C-1) or, equivalently, volts per meter (V m-1). The direction of the field at a point is defined by the direction of the electric force exerted on a positive test charge placed at that point. The strength of the field is defined by the ratio of the electric force on a charge at a point to the magnitude of the charge placed at that point. Electric fields contain electrical energy with energy density proportional to the square of the field intensity. The electric field is to charge as acceleration is to mass and force density is to volume.

A moving charge has not just an electric field but also a magnetic field, and in general the electric and magnetic fields are not completely separate phenomena; what one observer perceives as an electric field, another observer in a different frame of reference perceives as a mixture of electric and magnetic fields. For this reason, one speaks of "electromagnetism" or "electromagnetic fields." In quantum mechanics, disturbances in the electromagnetic fields are called photons, and the energy of photons is quantized.

Answer 2

Both A and B refer to the same thing. But I agree with the arguement that a large charge will disturb the field itself and so, B appears more correct.

C and D define the electric potential at a point and not the field strength.

Answer 3

As far as I can tell, both answers A and B are saying the same thing; both are almost correct definitions of the electric field strength.

To be absolutely correct, they should both say "the MAGNITUDE of the force...", because the question is asking about the field strength. Force is a vector quantity, whereas the electric field strength is a scalar. One can't define a scalar in terms of a vector. The magnitude of the force, however, is also a scalar, so this is how one should define the field strength.

Answer 4

Science is concerned with things we can observe or measure in some way or another. Therefore, "nothing" is outside of the scope of science. In physics, the word nothing is not used in any technical sense. A region of space is called a vacuum if it does not contain any matter, though it can contain physical fields. In fact, it is practically impossible to construct a region of space that contains no matter or fields, since gravity cannot be blocked and all objects at a non-zero temperature radiate electromagnetically. However, even if such a region existed, it could still not be referred to as "nothing", since it has properties and a measurable existence as part of the quantum-mechanical vacuum.

Answer 5

B. the charge must be small enough so that it does not modify the field itself.

Answer 6

A and B are ontologically equivalent, and so are both entirely correct definitions. This is a very badly set question.