EXPERIMENT 45 · PHYSICS LABORATORY
Electric Fields: Equipotential Mapping, Electric Field Lines, and Potential Gradient
To investigate the electrostatic potential distribution in a two-dimensional conducting medium for uniform parallel-plate and non-uniform dipole electrode configurations, map equipotential contours, verify the strict spatial orthogonality between electric field lines and equipotential surfaces, measure the electric potential gradient (E = −dV/dx), and determine the uniform electric field strength using ordinary least-squares linear regression. Explore a virtual apparatus, collect readings and analyse a graph.
FOLLOW THE METHOD
A reason behind every step.
To investigate the electrostatic potential distribution in a two-dimensional conducting medium for uniform parallel-plate and non-uniform dipole electrode configurations, map equipotential contours, verify the strict spatial orthogonality between electric field lines and equipotential surfaces, measure the electric potential gradient (E = −dV/dx), and determine the uniform electric field strength using ordinary least-squares linear regression. Suggested independent settings: 1.5, 3.0, 4.5, 6.0, 7.5, 9.0 cm.
1Substrate Preparation and Parallel Electrode Mounting
Fasten a fresh sheet of Teledeltos conducting paper smoothly onto the mapping board. Place the two parallel brass bar electrodes exactly d = 10.00 cm apart along the calibrated grid lines. Apply a thin line of colloidal silver conductive paint beneath each electrode to ensure flawless, uniform ohmic contact with the graphite substrate, and clamp firmly.
Why this step matters
Colloidal silver eliminates contact resistance variations along the electrode edges, ensuring the brass bars act as strictly equipotential boundary surfaces.
2Circuit Wiring and DC Voltage Calibration
Connect the positive terminal of the regulated DC power supply to the right electrode (+10.00 V) and the negative terminal to the left electrode (0.00 V / Ground). Connect the common (COM) ground lead of the digital voltmeter directly to the left grounded electrode, and connect the positive voltmeter lead to the handheld tracking probe.
Why this step matters
Grounding the negative electrode establishes an unambiguous zero-potential reference datum for all subsequent probe measurements across the board.
3Equipotential Line Mapping across Quadrants
Set the voltmeter to DC millivolts/volts. Gently touch the tracking probe to the conducting paper and locate points having potentials of exactly 2.00 V, 4.00 V, 6.00 V, and 8.00 V. For each voltage level, locate at least 7 distinct (x, y) coordinates spanning across the board, and record their positions on the coordinate grid sheet.
Why this step matters
Finding multiple points of equal potential maps the full two-dimensional contour lines of the electrostatic field.
4Orthogonal Electric Field Line Construction
Connect the points of equal potential with smooth continuous curves to produce equipotential lines. Using a drafting square, construct a family of electric field lines that start at the +10 V electrode and terminate on the 0 V electrode, ensuring every field line intersects every equipotential line at an angle of strictly 90°.
Why this step matters
Because electrostatic force is conservative, the gradient vector E = −∇V is perpendicular to surfaces of constant potential at every spatial point.
5Axial Potential Gradient Measurement
Position the tracking probe along the central longitudinal axis of symmetry (y = 0) where edge fringing fields are negligible. Record the local potential V for six discrete displacements x from the grounded electrode (x = 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 cm). Verify that the voltmeter reading stabilizes before logging data.
Why this step matters
Sampling along the central axis isolates the uniform one-dimensional potential gradient dV/dx, minimizing two-dimensional edge distortions.
6Dipole and Non-Uniform Geometry Exploration
Replace the parallel plates with two cylindrical point electrodes (+q and −q separated by 10 cm). Trace the resulting curved equipotential ovals and observe the convergence of electric field lines near the point poles, verifying that electric field density is greatest where equipotentials are closest together.
Why this step matters
Comparing planar and dipole geometries reinforces the universal relationship between field intensity, surface curvature, and equipotential line spacing.