# Question Video: Describing the Potential Difference Provided by a Cell Science

Which of the following terms refers to the potential difference provided by a cell in a circuit? [A] Electromagnetic force [B] Electrostatic force [C] Electromotive force [D] Electrochemical force

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### Video Transcript

Which of the following terms refers to the potential difference provided by a cell in a circuit? (A) Electromagnetic force, (B) electrostatic force, (C) electromotive force, (D) electrochemical force.

The question asks us to choose the term that refers to the potential difference provided by a cell in a circuit. Firstly, we can reject option (A), electromagnetic force, as there is no magnet present in a cell or in a conducting wire. So, any forces that act are unrelated to magnets. A cell stores chemical energy. When a cell is connected to a circuit, the chemical energy of the cell is released as electric energy. This suggests that the potential difference provided by a cell might be called electrochemical force. Is this correct though?

Firstly, we know that a potential difference exists when we separate opposite charges, and we know that these opposite charges attract each other and will move towards each other if they are not fixed in place. The force that acts on the charges is called electrostatic force. To separate opposite charges, work must be done on the charges. For a particular separation distance, the greater the charge that is separated, the more work required. The potential difference produced when opposite charges are separated is the work done on the charges to separate them per coulomb of charge that is separated.

It is important to understand that we have now described two different quantities: the force on each of a pair of opposite charges called electrostatic force and the work done per coulomb of separated charge called potential difference. This shows that potential difference is not the same quantity as electrostatic force. We reject option (B), electrostatic force. It is important to realize that work done per coulomb of separated charge is not actually any kind of force at all. Recall that work equals force multiplied by distance. This means that potential difference equals force times distance divided by charge, or equivalently, that potential difference equals force times the quantity distance divided by charge.

We see then that potential difference is not equal to force, but equal to force multiplied by distance divided by charge. It seems then that none of the answers are correct. In fact, the correct answer is option (C), electromotive force. But why?

The name “electromotive force” was invented a long time ago, when scientists studying electricity did not clearly understand what electric charge, electric current, electric potential difference, or electric energy were. Scientists at that time did not know that electrons existed; they only knew that a conducting wire connected to a cell seemed to have something flowing through it. This “something” was named “electricity” by the scientists, just so that they could call it by a name to distinguish it from other things.

The term “electromotive force” just means that which makes electricity move; it is not a force in the scientific meaning of force. Today, we know that a potential difference is not actually a force, but we still use the old term “electromotive force” as it was used so often by scientists in the past that since then scientists everywhere have become accustomed to using it.