A positive test charge is defined to be at a high electric potential when the charge is close to a positive source charge and a lower electric potential when the charge is held further away from the positive source, thus closer to the negative terminal. Electric potential is thus a function of the location of the positive charge in relation to its position in the electric field.
The electric potential of a positive test charge would thus be maximum when it is infinitely close to the positive terminal in a circuit, and it will be a minimum when the positive test charge is infinitely close to the negative terminal in a circuit. The electric potential cannot be negative.
The electric potential is similar to the gravitational potential, and we will use the example of the gravitational potential to understand electric potential better. Let’s look at how the gravitational force field of the earth imparts gravitational potential to an object based on its position above the earth’s surface.
Can Gravitational Potential Be Negative?
Gravitational potential energy is calculated by the formula:
U = mxgxh
- Where m is the mass of the object in kilograms
- g is the gravitational constant of 9.8 m/s/s at the surface of the earth
- h is the height of the object above the surface of the earth in meters
At the earth’s surface, the object’s height will be zero, and thus the gravitational potential at the surface will be zero. The gravitation potential will be positive at any distance above the earth’s surface. The gravitational potential energy is converted to kinetic energy as the object falls towards the earth.
Due to the Law of Conservation Of Energy, the Kinetic Energy and Potential Energy sum will remain constant. The gravitational potential is maximum at the point where the object is highest above the earth and lowest when it strikes the earth.
The gravitational potential cannot become negative as its lowest value is attained when the object has zero height above the earth.
The gravitational potential is thus a function of the position of an object of mass above the earth’s surface. Using the gravitational force field analogy, let’s consider the case for electrical charges between two charged plates.
Can Electric Potential Be Negative?
Electric potential is determined by the location of a charge within the electric field in which the charge finds itself. An electric force field will exist between two charged parallel plates where one plate is negatively charged, and the other is positively charged.
A positively charged point charge placed infinitely close to the positively charged plate will have its maximum electric potential. Like charges repel, the positive point charge will naturally want to move away from the positive plate with its maximum potential and move towards the negatively charged plate with its minimum electric potential.
Minimum Electric Potential
As is the case with the object hitting the earth’s surface and having zero gravitational potential when the positive charge comes infinitely close to the negatively charged plate, it will have its minimum electric potential.
At this point, the electric potential will tend towards zero but cannot become a negative amount.
Electrical work will have to be done on the point charge to move the positive point chargeback from the negative plate towards the positive plate again. This work can be done when chemical energy is used to move the chargeback to a position of higher electric potential.
In solar panels, the photon energy of the sunlight is used to provide the energy needed to move the positive charges back to a position of high electric potential.
The chemical energy of a battery or solar energy is used to reestablish the electric potential of the circuit by moving the charges back to higher electric potential.
When the battery has been fully discharged, and all the positive point charges have moved towards the point of lowest electric potential, the minimum cannot be below zero, and thus the electric potential can never be negative.
Electric Potential In Circuits – Where Is It The Highest And Lowest?
Consider a circuit consisting of a battery connected to a light bulb via electrical conductors leading from the negative and positive terminals of the battery to the two contact terminals on the light bulb. When the battery is fully charged, the electrical potential at the positive terminal is a maximum, and the negative one at a minimum.
The electric force field induced in the conductive wire is in the direction away from the positive terminal towards the negative terminal.
A positive charge moving from the point of maximum electric potential will lose potential energy as it moves along the conductive wire and through the resistance of the light bulb, where some of the energy will be converted to light energy.
Arriving at the negative terminal, the electrical potential of the charge will reach its minimum but cannot be lower than zero. Thus, the electrical potential will reach a minimum. The battery’s chemical energy will be converted to move the chargeback to the positive terminal again to repeat the cycle.
Once the chemical energy potential of the battery has been depleted such that it can no longer provide the energy needed to perpetuate the cycle, the light bulb will stop burning, and the positive charges accumulated at the negative terminal can no longer be returned to the positive terminal.
The battery will have to be recharged to provide the energy required to return the positive point charges to the positive terminal. This recharging can be achieved by connecting the terminals of the chemical battery up to a solar panel. The photons of the incident sunlight upon the photovoltaic cells will release energy that will recharge the battery.
Minimum Energy and Kinetic Maximum
Whether the potential is gravitational or due to an electric field, the potential can never become negative. It can merely reduce to a minimum. When an object hits the ground, its kinetic potential is maximum, and its gravitational potential is zero.
The same is true for a positively charged particle at the positive terminal. It has its maximum electric potential, and at the negative terminal, the electric potential is a minimum.