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By the end of the section, you will be able to:
Describe the electromotive force (emf) and the internal resistance of a battery
Explain the basic operation of a battery
If you forget to turn off your car lights, they slowly dim as the battery runs down. Why don't they suddenly blink off when the battery's energy is gone? Their gradual dimming implies that the battery output voltage decreases as the battery is depleted. The reason for the decrease in output voltage for depleted batteries is that all voltage sources have two fundamental parts—a source of electrical energy and an internal resistance. In this section, we examine the energy source and the internal resistance.

Introduction to Electromotive Force
Voltage has many sources, a few of which are shown in Figure 6.1.1. All such devices create a potential difference and can supply current if connected to a circuit. A special type of potential difference is known as electromotive force (emf). The emf is not a force at all, but the term ‘electromotive force’ is used for historical reasons. It was coined by Alessandro Volta in the 1800s, when he invented the first battery, also known as the voltaic pile. Because the electromotive force is not a force, it is common to refer to these sources simply as sources of emf (pronounced as the letters “ee-em-eff”), instead of sources of electromotive force.

(Figure 6.1.1) \begin{gather*}.\end{gather*}

The four parts of the figure show photos, part a shows a wind farm, part b shows a dam, part c shows a solar farm and part d shows three batteries.

By the end of the section, you will be able to:
Describe the electromotive force (emf) and the internal resistance of a battery
Explain the basic operation of a battery
If you forget to turn off your car lights, they slowly dim as the battery runs down. Why don't they suddenly blink off when the battery's energy is gone? Their gradual dimming implies that the battery output voltage decreases as the battery is depleted. The reason for the decrease in output voltage for depleted batteries is that all voltage sources have two fundamental parts—a source of electrical energy and an internal resistance. In this section, we examine the energy source and the internal resistance.

Introduction to Electromotive Force
Voltage has many sources, a few of which are shown in Figure 6.1.1. All such devices create a potential difference and can supply current if connected to a circuit. A special type of potential difference is known as electromotive force (emf). The emf is not a force at all, but the term ‘electromotive force’ is used for historical reasons. It was coined by Alessandro Volta in the 1800s, when he invented the first battery, also known as the voltaic pile. Because the electromotive force is not a force, it is common to refer to these sources simply as sources of emf (pronounced as the letters “ee-em-eff”), instead of sources of electromotive force.

(Figure 6.1.1) \begin{gather*}.\end{gather*}

The four parts of the figure show photos, part a shows a wind farm, part b shows a dam, part c shows a solar farm and part d shows three batteries.

By the end of the section, you will be able to:
Describe the electromotive force (emf) and the internal resistance of a battery
Explain the basic operation of a battery
If you forget to turn off your car lights, they slowly dim as the battery runs down. Why don't they suddenly blink off when the battery's energy is gone? Their gradual dimming implies that the battery output voltage decreases as the battery is depleted. The reason for the decrease in output voltage for depleted batteries is that all voltage sources have two fundamental parts—a source of electrical energy and an internal resistance. In this section, we examine the energy source and the internal resistance.

Introduction to Electromotive Force
Voltage has many sources, a few of which are shown in Figure 6.1.1. All such devices create a potential difference and can supply current if connected to a circuit. A special type of potential difference is known as electromotive force (emf). The emf is not a force at all, but the term ‘electromotive force’ is used for historical reasons. It was coined by Alessandro Volta in the 1800s, when he invented the first battery, also known as the voltaic pile. Because the electromotive force is not a force, it is common to refer to these sources simply as sources of emf (pronounced as the letters “ee-em-eff”), instead of sources of electromotive force.

(Figure 6.1.1) \begin{gather*}.\end{gather*}

The four parts of the figure show photos, part a shows a wind farm, part b shows a dam, part c shows a solar farm and part d shows three batteries.

By the end of the section, you will be able to:
Describe the electromotive force (emf) and the internal resistance of a battery
Explain the basic operation of a battery
If you forget to turn off your car lights, they slowly dim as the battery runs down. Why don't they suddenly blink off when the battery's energy is gone? Their gradual dimming implies that the battery output voltage decreases as the battery is depleted. The reason for the decrease in output voltage for depleted batteries is that all voltage sources have two fundamental parts—a source of electrical energy and an internal resistance. In this section, we examine the energy source and the internal resistance.

Introduction to Electromotive Force
Voltage has many sources, a few of which are shown in Figure 6.1.1. All such devices create a potential difference and can supply current if connected to a circuit. A special type of potential difference is known as electromotive force (emf). The emf is not a force at all, but the term ‘electromotive force’ is used for historical reasons. It was coined by Alessandro Volta in the 1800s, when he invented the first battery, also known as the voltaic pile. Because the electromotive force is not a force, it is common to refer to these sources simply as sources of emf (pronounced as the letters “ee-em-eff”), instead of sources of electromotive force.

(Figure 6.1.1) \begin{gather*}.\end{gather*}

The four parts of the figure show photos, part a shows a wind farm, part b shows a dam, part c shows a solar farm and part d shows three batteries.