Both obey inverse-square laws
Electric Fields - OCR A-Level Physics
- Both obey inverse-square lawsLaws where a quantity is inversely proportional to the square of the distance, e.g. gravitational and Coulomb force.: F \propto 1/\(r^{2}\).
- Both have a field strength defined as force per unit mass/chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). and a potential defined as energyThe capacity to do work. Measured in joules (J). per unit mass/chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)..
- Gravity is always attractive; electric forces can be attractive or repulsive.
- Gravitational potentialThe work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). times potential difference). per unit mass in bringing a small test mass from infinity to that point. Always negative. Measured in J kg⁻¹. is always negative (defined as zero at infinity, work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). against the field is negative). Electric potentialThe work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). per unit positive charge in bringing a small test charge from infinity to that point. can be positive or negative depending on the sign of the source charge.
- Gravitational fieldA region of space in which a mass experiences a gravitational force. lines always point towards mass. Electric field lines point away from positive charges and towards negative charges.
- The gravitational constant G is extremely small (6.67 × 10⁻¹¹); the CoulombThe SI unit of charge. One coulomb is the charge transferred by a current of 1 A in 1 second. constant k is very large (8.99 × 10⁹). Electric forces between fundamental particles are vastly stronger than gravitational forces.
Examiner Tips and Tricks
- Comparison questions are common 6-mark responses.
- Structure your answer clearly: state a similarity, then the corresponding difference, using equations from both topics.
- Use terms like 'analogous' and 'however' to link points.