OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(a) electric potential at a point as the work done in bringing unit…
Full specification wording
Electric potential and energy: (a) electric potential at a point as the work done in bringing unit positive charge from infinity to the point; electric potential is zero at infinity
Electric potential at a point is defined as the work done per unit positive charge in bringing a small test charge from infinity to that point.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electric potential at a point is defined as the work done per unit positive charge in bringing a small test charge from infinity to that point. The zero of potential is taken at infinity, meaning that at an infinite distance from the charge creating the field, the potential is exactly zero. The work done W in moving a charge q between two points with potential difference ΔV is W = qΔV. For example, if a charge of +2.0 μC is moved through a potential difference of 500 V, the work done is W = (2.0 × 10⁻⁶) × 500 = 1.0 × 10⁻³ J. You must be able to define electric potential and understand its zero reference at infinity.
What earns the marks
- Define electric potential as work done per unit positive charge from infinity to the point.
- State that electric potential is zero at infinity.
- Calculate work done using W = qΔV.
- Recognise that potential is a scalar quantity and can be positive or negative depending on the sign of the source charge.
Common mistakes and how to put them right
Confusing electric potential with electric potential energy.
Put it right: Potential is work done per unit charge, while potential energy is work done on a specific charge.
Forgetting the zero reference at infinity.
Put it right: State that potential is zero at infinity when defining it.
Mixing up potential difference and potential.
Put it right: Potential difference is the difference in potential between two points.
Exam tips
- Remember that electric potential is a scalar, so no direction is needed.
- When calculating work done, ensure the charge and potential difference have consistent signs.
- Use the definition precisely: work done per unit positive charge from infinity.
Try the lesson
The start of the Electric potential and energy: (a) electric potential at a point as the work done in bringing unit positive charge from infinity to the point; electric potential is zero at infinity lesson, made from checked teaching notes for this specification point.
Listen
Electric potential at a point is defined as the work done per unit positive charge in bringing a small test charge from infinity to that point. The zero of potential is taken at infinity, meaning that at an infinite distance from the charge creating the field, the potential is exactly zero. The work done W in moving a charge q between two points with potential difference ΔV is W = qΔV. For example, if a charge of +2.0 μC is moved through a potential difference of 500 V, the work done is W = (2.0 × 10⁻⁶) × 500 = 1.0 × 10⁻³ J. You must be able to define electric potential and understand its zero reference at infinity. A strong answer earns marks for these points. Define electric potential as work done per unit positive charge from infinity to the point. State that electric potential is zero at infinity. Calculate work done using W = qΔV. Recognise that potential is a scalar quantity and can be positive or negative depending on the sign of the source charge. A common slip: Confusing electric potential with electric potential energy. Instead, potential is work done per unit charge, while potential energy is work done on a specific charge. Exam tip: Remember that electric potential is a scalar, so no direction is needed.
See it
Key words
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Electric potential
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Zero at infinity
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Potential difference
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Work done
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See every definition
- Electric potential
- The work done in bringing unit positive charge from infinity to the point.
- Zero at infinity
- Electric potential is zero at infinity.
- Potential difference
- The difference in potential between two points, where the work done W in moving a charge q between them is W = qΔV.
- Work done
- Calculated using W = qΔV when a charge moves through a potential difference.
Label the diagram
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