EMF和电位差之间的差异

在现实生活中使用电池和电池时，我们会遇到电池端子之间的两种不同的电位差。这些电位差是由于电池的非理想性质导致的，这会增加电池内部的电阻。电位器用于测量这种差异。这些不同的值称为电动势和电池的电位差。要了解为什么会出现这种现象，我们需要查看电路和电池提供的电阻。让我们详细看看这些概念。

电池的电动势 (EMF)

由电池传递给单位电荷的能量称为电动势 EMF。电池有多种形式和尺寸可供选择。有许多不同类型的发电机由各种来源供电。所有这些设备，无论其能源是什么，都会在其端子之间产生电位差，并且如果将电阻连接到它们，则可以提供电流。众所周知，电位差会产生电场，使电荷移动，进而产生电流。因此，这种电位差有时也称为电动势 (emf)。

与它的名字相反，电动势根本不是一种力量。这是一个潜在的差异。如果准确地说，

E.M.F is a potential difference which is created when no current is flowing in the system. 

它的单位被认为是伏特（V）。尽管 EMF 与电压源产生的电位差直接相关，但仍与反映在电池端子上的实际电位差不同。电池周围的端电压通常小于电池的电动势。

电池的电位差

电池的电压输出是通过其端子测量的，这就是为什么它被称为端子电压。在下图中，显示了电池及其内部电阻。电池串联到另一个外部电阻，用 R _load表示。电池两端产生的净电压由下面的公式给出，

V = 电动势 – Ir

这里，“I”是在电路中流动的电流，“r”是内部电阻。

如果“I”的流动方向是从电池的负极到正极，则“I”被认为是正极。该等式表明，电流越大，电池的端电压越低。也可以得出，内阻越小，端电压越大。当考虑负载电阻时，电流计算变得有点不同。

The equivalent resistance of the circuit becomes, 

R = r + R_load

The current is given by Ohm’s law, 

$I = \dfrac{\text{emf}}{R_{\text{load}} + r}$

EMF和电位差之间的差异

Electromotive Force (E.M.F)	Potential Difference
The difference in the potential of two electrodes of a battery.	Difference of potential between any two points on the circuit.
E.M.F is always greater than the potential difference between any points in the circuit.	This is always less than the E.M.F
Formula: E = I(R + r)	Formula: V = IR
This is caused by the electric, gravitational and magnetic fields.	This difference is only produced by the electric field.
The electromotive force is the amount of energy given to each coulomb of charge.	The potential difference is the amount of energy utilized by one coulomb of charge.
The electromotive force is independent of the circuit’s internal resistance.	The potential difference is proportional to the circuit’s resistance.
The electromotive force is responsible for transferring energy across the circuit.	The potential difference between any two places on the circuit is a measure of energy.
When the circuit is unchanged, the magnitude of the electromotive force is always larger than the potential difference.	When the circuit is completely charged, the size of the potential difference is equal to the circuit’s emf.
The electromotive force is measured using an emf meter.	The potential difference is measured with a voltmeter.

示例问题

问题 1：找出将在 2 伏特和 0.02 欧姆内阻的电池内部流动的电流，以防其端子相互连接。

解决方案：

The current in that case will be given by simple application of ohm’s law. 

V = 2V 

r = 0.02 ohms. 

V = IR 

Plugging the values in the equation, 

I = V/R 

I = 2/0.02 

   = 100 A 

问题 2：找出将在 10 伏特和 5 欧姆内阻的电池内部流动的电流，以防其端子相互连接。

解决方案：

The current in that case will be given by simple application of ohm’s law. 

V = 10 V 

R = 5 ohms. 

V = IR 

Plugging the values in the equation, 

I = V/R 

I = 10/5 

 = 2 A 

问题 3：找出将在 10 伏特和 10 欧姆内阻的电池内部流动的电流，以防其端子相互连接。求电池的端电压。

解决方案：

The current in that case will be given by simple application of ohm’s law. 

V = 10 V 

R= 10 ohms. 

V = IR 

Plugging the values in the equation, 

I = V/R 

 I = 10/10

  = 1 A

The terminal voltage of the battery is given by, 

V = emf – Ir

Given , emf = 10 V, I = 1A and r = 10

V = emf – Ir

  = 10 – (1)(10) 

  = 0 V 

问题 4：找出将在 10 伏和 5 欧姆内阻和 5 欧姆负载电阻串联的电池内部流动的电流。求电池的端电压。

解决方案：

The current in that case will be given by simple application of ohm’s law. 

I = $\frac{\text{emf}}{R_{\text{load}} + r}$

emf = 10 V 

R_load= 5 ohms. 

r = 5

Plugging the values in the equation, 

I = $\frac{\text{emf}}{R_{\text{load}} + r}$

I = 10 / (5 + 5)

 = 1 A 

The terminal voltage of the battery is given by, 

V = emf – Ir

Given , emf = 10 V, I = 1 A and r = 5

V = emf – Ir

  = 10 – (1)(5) 

 = 10 – 5 

 = 5 V

问题 5：找出将在 10 伏特和 2 欧姆内阻和 3 欧姆负载电阻串联的电池内部流动的电流。求电池的端电压。

解决方案：

The current in that case will be given by simple application of ohm’s law. 

I = $\frac{\text{emf}}{R_{\text{load}} + r}$

emf = 10 V 

R_load= 3 ohms. 

r = 2

plugging the values in the equation, 

I = $\frac{\text{emf}}{R_{\text{load}} + r}$

⇒ I = $\frac{10}{2 + 3}$

⇒ I = 2 A 

The terminal voltage of the battery is given by, 

 V = emf – Ir

Given , emf = 10 V, I =2 A and r = 2

 V = emf – Ir

   = 10 – (2)(2) 

   = 10 – 6

  = 4V