päättyjännitteellä

Päättyjännitteellä, often translated as "terminal voltage" in English, refers to the electrical potential difference measured across the terminals of a device, such as a battery or a generator, when it is either supplying or receiving current. This voltage is distinct from the open-circuit voltage, which is the voltage measured when no current is flowing. The difference between the open-circuit voltage and the terminal voltage is due to internal losses within the device.

For a source like a battery, the terminal voltage is typically lower than the open-circuit voltage when current is being drawn. This reduction is caused by the internal resistance of the battery. The current flowing through this internal resistance creates a voltage drop, which subtracts from the electromotive force (EMF) of the battery. Mathematically, for a source, the terminal voltage (V_t) can be expressed as V_t = EMF - I * R_int, where EMF is the electromotive force, I is the current, and R_int is the internal resistance.

Conversely, when a device like a battery is being charged, its terminal voltage will be higher than its EMF. This is because the charging current flows in the opposite direction through the internal resistance, causing a voltage rise across it. In this case, V_t = EMF + I * R_int. Understanding terminal voltage is crucial in analyzing the performance and efficiency of electrical power sources and loads.

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