Physics · Electrostatic Potential And Capacitance · NEET
No. Electric potential (V) is a single value AT one point, found by bringing a unit charge from infinity to that point. Potential difference is V_B − V_A, comparing TWO points. Potential needs a reference (infinity = 0); potential difference is a subtraction, so the reference cancels out. For NEET, most numericals actually use potential difference because it is what does measurable work.
When you move charge q slowly from A to B, you do work W_AB against the electric force. This work depends on q. To get a quantity that describes the two points only (not the size of the test charge), divide by q. So V_B − V_A = W_AB / q. That is why the unit is joule per coulomb, called the volt.
It is a scalar. It has magnitude and a sign (+ or −) but no direction in space. You cannot add potential differences as vectors; you add them algebraically. This is why potential is easier than electric field in many NEET problems — no components, just plus and minus.
No. The electrostatic force is conservative, so the work done in moving a charge from A to B is the same for every path. Therefore V_B − V_A depends only on the two end points, not on the route. Over any closed loop the total work is zero, so the potential difference around a closed path is zero.
EMF is the work done per unit charge by a source (like a battery) to push charge through the whole circuit, including inside the source. Potential difference is measured across two points in the circuit. When current flows, terminal potential difference is less than EMF because of internal resistance. For pure electrostatics (no current), the terms are often used loosely, but EMF belongs to sources.
A thin spherical shell is charged by some source. The potential difference (in V) between a point C and a point P, both lying inside the shell, is (Take 1/4πε₀ = 9 × 10⁹ SI units).
A unit positive point charge is taken slowly through a thin tube inside a uniformly charged dielectric sphere of radius R and charge density ρ. The initial and final positions A and B are at distances 2R and 3R from the centre. The magnitude of total work done is ρR²/(nε₀). Find n.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The volt (V). One volt = one joule per coulomb (1 V = 1 J/C). It means 1 joule of work is done to move 1 coulomb of charge between the two points.
V_B − V_A = W_AB / q, where W_AB is the work done by an external agent to move charge q slowly from A to B. In a uniform field, V = E·d (magnitude), where d is the distance along the field.
Yes. If you move a unit positive charge from a high-potential point to a low-potential point, the external work is negative, so V_B − V_A is negative. The sign simply tells you which point is at higher potential.
Only differences do measurable work and drive current. Absolute potential needs a reference (infinity), which is not practical in a circuit, so we compare two points instead. Voltmeters always read a difference.
The potential difference between any two points ON the same equipotential surface is zero. That is the definition of an equipotential surface, so no work is done moving a charge along it.
