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Open-circuit voltage

Open-circuit voltage is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Open-circuit voltage rather than just read about it. In short: Open-circuit voltage (OCV or VOC) is the difference of electrical potential between two terminals of an electronic device when disconnected from any circuit. Voltage There is no external load connected.

Open-circuit voltage — main illustration
Open-circuit voltage — illustration

Key takeaways

  • Open-circuit voltage belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Open-circuit voltage to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Open-circuit voltage from memory before moving on to harder problems.

Reference excerpt

Open-circuit voltage (OCV or VOC) is the difference of electrical potential between two terminals of an electronic device when disconnected from any circuit.

Voltage There is no external load connected. No external electric current flows between the terminals. Alternatively, the open-circuit voltage may be thought of as the voltage that must be applied to a solar cell or a battery to stop the current. It is sometimes given the symbol Voc. In network analysis this voltage is also known as the Thévenin voltage. The open-circuit voltages of batteries and solar cells are often quoted under particular conditions (state-of-charge, illumination, temperature, etc.). The potential difference mentioned for batteries and cells is usually the open-circuit voltage. The value of the open-circuit voltage of a transducer equals its electromotive force (emf), which is the maximum potential difference it can produce when not providing current.

Example Consider the circuit:

If we want to find the open-circuit voltage across the 5Ω resistor, first disconnect it from the circuit:

Find the equivalent resistance in loop 1 to find the current in loop 1. Use Ohm's law with that current to find the potential drop across the resistance C. Note that since no current is flowing through resistor B, there is no potential drop across it, so it does not affect the open-circuit voltage. The open-circuit voltage is the potential drop across the resistance C, which is: C C + A 100 V ∼ . {\textstyle {\frac {C}{C+A}}\ 100\ V_{\sim }\ .}

This is just an example. Many other ways can be used.

See also Short circuit

References

Illustrations

Open-circuit voltage: Definition of open-circuit voltage. The box is any two-terminal device, such as a battery or solar cell. The two terminals are not connected to anything (an open circuit), so no current can flow into or out of either terminal. The voltage voc between the terminals is the open-circuit voltage of the device.
Definition of open-circuit voltage. The box is any two-terminal device, such as a battery or solar cell. The two terminals are not connected to anything (an open circuit), so no current can flow into or out of either terminal. The voltage voc between the terminals is the open-circuit voltage of the device.
Open-circuit voltage: Black curve: The highest possible open-circuit voltage of a solar cell in the Shockley–Queisser model under unconcentrated sunlight, as a function of the semiconductor band gap. The red dotted line shows that this voltage is always smaller than the band gap voltage.
Black curve: The highest possible open-circuit voltage of a solar cell in the Shockley–Queisser model under unconcentrated sunlight, as a function of the semiconductor band gap. The red dotted line shows that this voltage is always smaller than the band gap voltage.
Open-circuit voltage: Given Circuit
Given Circuit
Open-circuit voltage: Modified circuit
Modified circuit

Worked examples

Example 1 — a first encounter with Open-circuit voltage

Start with the simplest possible case. Write down what Open-circuit voltage claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Open-circuit voltage before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Open-circuit voltage ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Open-circuit voltage

In research
Open-circuit voltage appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Open-circuit voltage in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Open-circuit voltage is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrical parameters, so understanding it makes those chapters shorter.
In everyday life
Look for Open-circuit voltage outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Open-circuit voltage in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Open-circuit voltage means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Open-circuit voltage out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Open-circuit voltage in simple terms?

Open-circuit voltage (OCV or VOC) is the difference of electrical potential between two terminals of an electronic device when disconnected from any circuit. Voltage There is no external load connected.

Why does Open-circuit voltage matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Open-circuit voltage?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Open-circuit voltage.

Tags

  • Electrical parameters

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