Terminal Voltage Discharge — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Terminal Voltage During Discharge This formula applies when a battery or electrochemical cell is discharging current (I) through an external load resistance, accounting for internal energy losses. Define the Electromotive Force (EMF), , as the maximum voltage generated by the cell. Apply Ohm's law to the entire circuit, recognizing that the total voltage drop is the terminal voltage V. The terminal voltage is given by V = - Ir, where Ir is the voltage drop across the internal resistance r. Power delivered to the load is P load = I V = I( - Ir). Efficiency is defined as the ratio of useful power output to the chemical power input: = P load / P chem . Current (I) must be non-negative. Internal resistance (r) must be non-negative. The terminal voltage V = - Ir must be non-negative for the battery to function. Assuming the terminal voltage (V) is always equal to the EMF ( ), ignoring the voltage drop across internal resistance. Confusing the internal resistance (r) with the external load resistance (R). Treating the power equations as additive when they represent energy conversion paths (e.g., P load P chem - P int ).