Static electricity in our everyday lives
We get to experience static electricity in our daily lives in a plethora of ways. Some are listed below:
- You may notice tiny sparks when taking off clothes made of synthetic fibres.
- Ever realised a small shock when getting out of a car? An electrostatic charge builds up on the car, and then discharges through you when you touch the metal door.
- When you rub a balloon on clothes you may observe how it sticks to the wall or to the ceiling
- When you rub a plastic ruler with a cloth, both are likely to become electrically charged.
These are wonders of static electricity.
Now let look at why these phenomena occur. Here is an example:
A plastic rod is rubbed with a cloth so that both become charged. The rod is hung to a cradle which enables it to move freely. When a cloth is brought nearer to the rod, it moves towards the cloth. This is an electrostatic attraction.
If a second rod is rubbed in the same way and brought close to the first one the hanging rod moves away. This is electrostatic repulsion.
The above example suggests that there are two types of static electricity:
- Positive charge
- Negative charge
From the example below we can also say something about the forces on the forces exerted by electric charges on each other:
- Like charges repel
- Unlike charges attract
Note: Please do not confuse magnetism with static electricity!
Magnetism arises from magnetic poles – static electricity arises from electric charges.
It doesn’t matter whether an object is charged or uncharged: a single charged object can affect both without touching it.
We say that there is an electric field around a charged object. Any other charged object placed in this field will experience a force exerted on it.
Explaining static electricity
It is the force of friction which causes charging. When a plastic rod is rubbed with a cloth, friction transfers electrons from one material to other.
For example: if the rod is made up of polyethene it is usually the case that electrons are rubbed off the cloth and to the rod.
Electrons are part of every atom. They are negatively charged and are found outside of the atom. They are weakly held in atoms and so they can be easily pulled away by the force of friction. This causes the atom to become positively charged when the electrons are pulled away by friction.
Charging by induction
As seen before charged objects can attract uncharged objects. Try this: Scatter some tiny pieces of paper on a desk.
- Rub a polyethene rod on a woollen cloth.
- Both the charged rod and the charged cloth will attract the paper.
- This is the same effect as rubbing a balloon on clothes and sticking on a wall
- An uncharged object (the wall) is attracted by the charged one (the balloon)
Wondering how this happens?
Let’s see how:
- Suppose the balloon has a positive charge.
- It must be attracted to a negative charge in the wall
- The wall itself is neutral, as it is made up of positively and negatively charged particles.
- When the balloon is brought close to the wall its electrons moves towards the balloon, because they are attracted by it.
- This brings the negatively charged particles towards the surface of the wall.
- This effect is enough to give the surface of the wall a negative charge.
We say that a negative charge has been induced on the wall. This is entire process is known as charging by induction.
Representing an electric field
A charged object is surrounded by an electric field. If another charged object moves into this electric field it experiences a force being exerted on it. This causes the objects to attract or repel each other.
We can represent an electric field by lines of force (or electric field lines) (this is similar to magnetic field lines) the lines of force are shown coming out of a positive charge and going into a positive charge. This is because the lines indicate the direction of the force on a positive charge placed in the field. A positive charge is repelled by another positive charge and is attracted by a negative charge.
When two oppositely charged objects are placed close to each other they attract one another. Similarly, two objects with the same charge repel each other.
When two oppositely charged parallel plates are brought together the lines of forces between the plates are straight and parallel to one another except at the edges.
What is an electric charge?
The electric force between two charged objects is one of the fundamental forces of nature. The electric force holds the particles that make up an atom together. It holds atoms together to make solid objects.
So when you stand on the floor, it is actually the electric force between the molecules that prevents you from falling through the floor! This makes it an important example of static electricity.
Charged particles and static electricity
As seen before, electrons are negatively charged particles that are transferred from one object to another, when exposed to the force of friction. An electron is weakly held by the positively charged nucleus, containing protons.
Electric charge is a property of particles that make up atoms.
Electric charge is measured in coulombs (C).
An electron has a very minute amount of electric charge. The electron charge is so small that it takes about 6 million million million electrons to make 1C of charge!
Electron charge =
It is astonishing to know that a proton has the same amount of charge as an electron. This means that the overall atom has no relative charge and is said to be neutral. This is vital for the world or else we would have been a part of an extremely shocking world!
PHET Simulation for Static Electricity
Here is a PHET Simulation for Static Electricity:
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