Question:
The current densities in human bodies lie in the proximity of the transmission line are:
The current densities in human bodies lie in the proximity of the transmission line are:
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The human body acts as a shield against ELF electric fields, concentrating them on the surface and causing high internal current induction. Conversely, it is virtually transparent to ELF magnetic fields, resulting in minimal internal eddy current induction.
Updated On: Jun 25, 2026
- induced by electric fields are much lower than those induced by magnetic fields
- induced by electric fields only
- induced by electric fields are much higher than those induced by magnetic fields
- induced by magnetic field only
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The Correct Option is C
Solution and Explanation
Concept:
Extremely Low Frequency (ELF) electromagnetic fields are produced by high-voltage overhead transmission lines (typically operating at $50\text{ Hz}$ or $60\text{ Hz}$). When a human body is positioned on the ground beneath a transmission line, it is exposed to both an electric field (due to line voltage) and a magnetic field (due to line current). These external fields interact with the conducting tissues of the body to induce internal electric currents and charge distributions:
* Electric Field Coupling: Occurs via capacitive displacement coupling. The human body is an excellent conductor relative to air, which causes distortion in the local electric field and induces a significant surface charge density, leading to internal current flow down to the ground.
* {Magnetic Field Coupling: Occurs via Faraday electromagnetic induction. The time-varying magnetic field induces internal circulating eddy currents inside body tissue loops.
Step 1: Quantify the capacitive coupling from electric fields.
The external electric field ($E$) lines terminate perpendicularly on the human skin. The total current $I_e$ induced in a human body standing on the ground in an electric field is proportional to the frequency ($f$) and the field strength: \[ I_e \propto f \cdot E \] At high voltages (e.g., $400\text{ kV}$ or $765\text{ kV}$ lines), the electric field at ground level can reach several kilovolts per meter ($\text{kV/m}$). This high field strength induces internal current densities on the order of several microamperes per square meter ($\mu\text{A/m}^2$).
Step 2: Quantify the inductive coupling from magnetic fields.
The current density $J_m$ induced inside a circular tissue loop of radius $r$ by a time-varying magnetic flux density $B$ is given by Faraday's Law: \[ J_m = \sigma \cdot E_{\text{induced}} = \sigma \cdot \pi \cdot f \cdot r \cdot B \] where $\sigma$ is the electrical conductivity of human tissue. Since the magnetic flux density directly beneath standard transmission lines at ground level is relatively low (often in the microtesla range, $\mu\text{T}$), the resulting induced internal current density is very small.
Step 3: Compare the two values.
Comparing the physiological induction mechanisms shows that the internal current densities induced by the intense static capacitive electric fields are higher than those induced by the magnetic fields under standard operating conditions. Therefore, Option (C) is the accurate choice.
Step 1: Quantify the capacitive coupling from electric fields.
The external electric field ($E$) lines terminate perpendicularly on the human skin. The total current $I_e$ induced in a human body standing on the ground in an electric field is proportional to the frequency ($f$) and the field strength: \[ I_e \propto f \cdot E \] At high voltages (e.g., $400\text{ kV}$ or $765\text{ kV}$ lines), the electric field at ground level can reach several kilovolts per meter ($\text{kV/m}$). This high field strength induces internal current densities on the order of several microamperes per square meter ($\mu\text{A/m}^2$).
Step 2: Quantify the inductive coupling from magnetic fields.
The current density $J_m$ induced inside a circular tissue loop of radius $r$ by a time-varying magnetic flux density $B$ is given by Faraday's Law: \[ J_m = \sigma \cdot E_{\text{induced}} = \sigma \cdot \pi \cdot f \cdot r \cdot B \] where $\sigma$ is the electrical conductivity of human tissue. Since the magnetic flux density directly beneath standard transmission lines at ground level is relatively low (often in the microtesla range, $\mu\text{T}$), the resulting induced internal current density is very small.
Step 3: Compare the two values.
Comparing the physiological induction mechanisms shows that the internal current densities induced by the intense static capacitive electric fields are higher than those induced by the magnetic fields under standard operating conditions. Therefore, Option (C) is the accurate choice.
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