Electric Potential (OCR A Level Physics): Revision Note

Electric Potential

• In order to move a positive charge closer to another positive charge, work must be done to overcome the force of repulsion between them

  • Similarly, to move a positive charge away from a negative charge, work must be done to overcome the force of attraction between them

• Energy is therefore transferred to the charge that is being pushed upon

  • This means its potential energy increases

• If the positive charge is free to move, it will start to move away from the repelling charge

  • As a result, its potential energy decreases back to 0

• This is analogous to the gravitational potential energy of a mass increasing as it is being lifted upwards and decreasing as it falls

• The electric potential at a point is defined as:

  The work done per unit positive charge in bringing a point test charge from infinity to a defined point

• Electric potential is a scalar quantity

  • This means it doesn’t have a direction

• Even though electric potential is a scalar quantity, it can take a positive or negative sign, this is because the electric potential is:

  • Positive around an isolated positive charge

  • Negative around an isolated negative charge

  • Zero at infinity

• Positive work is done by the mass from infinity to a point around a positive charge and negative work is done around a negative charge. This means:

  • When a positive test charge moves closer to a negative charge, its electric potential decreases

  • When a positive test charge moves closer to a positive charge, its electric potential increases

• To find the potential at a point caused by multiple charges, the total potential is the sum of the potential from each charge

The electric potential V decreases in the direction the test charge would naturally move in due to repulsion or attraction