Difference Between Static and Current Electricity

Main Difference – Static vs. Current Electricity

Static and current electricity refer to the phenomena related to the behaviour of electrical charges. The main difference between static and current electricity is that the term static electricity refers to situations where there is an excess of charges in a region without there being a net flow of charge, whereas current electricity refers to cases where there is a net flow of charge in response to a potential difference.

What is Static Electricity

Atoms that make up materials consist of protons and electrons. Protons are positively charged whereas electrons are negatively charged. In electrically neutral materials, the number of protons is equal to the number of electrons, and so there is no net charge. When some material are rubbed together, electrons can get transferred from one material to the other. The material that loses electrons now becomes positively charged whereas the material that gains electrons becomes negatively charged.

The like charges repel each other while unlike charges attract. If you rub a polythene rod with a piece of cloth, some electrons from the cloth get transferred onto the rod, making the rod negatively charged. If you bring the rod close to a slow, steady stream of water from a tap, you can see that the water moves towards the rod. This is because the negative charges in water move away from the polythene rod, making the water closer to the polythene rod more positive. Since like charges attract, the water stream now bends towards the rod. A demonstration of this effect is shown in the video below:

When a material is charged, the excess charges are repelling each other. So, whenever possible, they try to move about and make the material neutral again so as to minimize repulsion. However, if the material is surrounded by an insulator, the charges cannot flow to another place and so the material remains charged. The term static electricity describes this type of situation when an excess-charge accumulation occurs, with no way for charges to move about and make the material neutral again. Note that in terms of protons and electrons, it is always the electrons that can move about. So if a material is negatively-charged, electrons attempt to flow out of the material and if a material is positively-charged, electrons attempt to flow into the material.

Sometimes, though, if there is a large number of excess charges the repulsion is so high that electrons have enough energy to flow through an insulator. This is what happens during a lightning strike. Thunderclouds become charged as they rub against each other in the atmosphere. If enough charges build up in the cloud, electrons can flow between the ground and the cloud in order to neutralize the cloud. The discharge of electrons is rapid, and this is what we experience as lightning.

Van de Graaff generators are also used to demonstrate static electricity. In these, there is a rubber belt that rubs against a brush to create charges. These charges get accumulated on a dome. If a person touches the dome while standing on an insulator, their hair “stands on end” because their hair gets charged by the same charge and starts repelling. If a small metal sphere is brought very close to a charged Van de Graaff generator, the excess charges get transferred quickly in the form of a spark. This process is the same as what happens during lightning.

Difference Between Static and Current Electricity - Discharge_from_a_Van_de_Graff_Generator

The dome of a Van de Graaff generator discharging

What is Current Electricity

Current is a term that is used to describe a net flow of charge. Specifically, current refers to the rate of flow of charge. The flow of charge is set up by a potential difference. If charge is given by $Q$ , then the electric current $I$ is:

$I=\frac{\mathrm dQ}{\mathrm dt}$

Almost all of the electric currents we deal with consist of a flow of electrons. Conventionally, we take the direction of the current to be in the direction opposite to the direction of flow of electrons. In the way we use electric current, we drive them around in circuits, and we need to use energy to maintain a potential difference so that charges continue to flow.

There are two main types of current: in direct current, the potential difference driving the current maintains its direction. Consequently, electrons continually flow along one direction. In alternating current, the potential difference is constantly made to change direction and, in response, electrons are also moving back-and-forth. As electrons flow, they give out their energy. Electrical devices work by making use of this energy given off by electrons.

Interestingly, a moving charge always produces a magnetic field around it. Therefore, whenever a current is flowing in a wire, there is a magnetic field around it. We can use this property to create electromagnets.

Difference Between Static and Current Electricity

Charge Flow

In static electricity, there is an excess of one type of charge in a region. However, there is no net flow of charge.

In current electricity, charges flow in response to a potential difference.

Constant Flow of Current

In static electricity, the discharges happen when a large enough charge accumulates. It is not possible to maintain a constant flow of charge without giving time for the material to accumulate charges again.

In current electricity, we can maintain a constant flow of current by giving energy to the system.