The terminal voltage of the battery in the open circuit state is called the open circuit voltage.The open circuit voltage of the battery is equal to the difference between the positive electrode potential and the negative electrode potential of the battery when the battery is open circuit (i.e. when no current passes through the two poles).
The open circuit voltage of the battery is expressed as V open, i.e. V open=Ф+-Ф-，amongФ+、Ф-They are respectively the positive and negative electrode potentials of the battery.The open circuit voltage of the battery is generally less than its electromotive force.This is because the electrode potential established by the two poles of the battery in the electrolyte solution is usually not the equilibrium electrode potential, but the stable electrode potential.Generally, it can be approximated that the open circuit voltage of the battery is the electromotive force of the battery.
Difference between open circuit voltage and potential
The essence of potential is the interface behavior between two contacting phases. The electromotive force of the battery is qualitatively different from the open circuit voltage. The electromotive force is the difference between the balance potential of the two poles, and the open circuit voltage is the difference between the stable potential of the positive and negative poles[1]。
essence
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The open circuit voltage refers to the potential difference between the positive and negative poles when no current passes through the battery. In the actual battery system, the potential established by the two poles of the battery is mostly stable potential, so the open circuit voltage is actually the difference between the stable potential of the two poles.The open circuit voltage is a measured value, which is usually less than the value of the electromotive force of the battery. Generally, the higher the reversibility of the battery system, the closer the open circuit voltage is to the value of the electromotive force. Only when the battery system is in the thermodynamic reversible state, the two values are equal[1]。
Causes
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For a basic circuit with power supply, connecting conductor and load, if there is an open circuit somewhere, the voltage between the two disconnection points is the open circuit voltage.When the circuit is open, we can understand that an infinite resistance is connected to the open circuit. There is no doubt that the infinite resistance is connected in series with the circuit. According to the voltage division formula of the resistance in the series circuit, the voltage division at both ends of the infinite resistance will be the highest voltage in the circuit, that is, the power supply voltage.Therefore, when the line is open, the open circuit voltage is generally expressed as the supply voltage.
actual measurement
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In actual calculation, it can be considered that there is aVoltmeter, the voltmeter reading is the open circuit voltage.However, when measuring the open circuit voltage of dry battery, the data read out by magnetoelectric instrument and digital voltmeter are often different, sometimes the difference is about 30 mV[2]Therefore, the following steps should be followed when measuring:
Open circuit voltage
1. When reading the pointer voltmeter, the eyes should face up, and the needle should coincide with the mirror needle and the dial scale[2]。
2. The range shall be between 1/3-r2/3 of the dial[2]。
3. The measuring wire should have a good contact end[2]。
4. Then correct the phenotypes listed in the picture with reference to the resistance parameters of various specifications and the measured actual values[2]。
When the internal resistance of the battery is fixed, if the internal resistance of the voltmeter is large, the indicated value will be closer to the actual value. If the internal resistance of the voltmeter is small, the error of the indicated value will be large. "When the battery capacity is large, its internal resistance is small, and the error of open circuit voltage measured by different types of voltmeters is small. The internal resistance of digital voltmeters is much larger than that of magnetoelectric voltmeters. The open circuit voltage measured by digital voltmeters is closer to the actual open circuit voltage of batteries, and the measured data is more reliable[2]。
influence factor
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The main factors affecting the open circuit voltage include the nature of the battery bipolar system, the nature of the material, the composition and concentration of the solution, temperature, and the state of the electrode boundary[1]。If the positive and negative materials of the battery are identical, the open circuit voltage is the same no matter how large the battery volume is and how the geometric structure changes.
