# 8 Coulomb’s Law Examples in Daily Life

Coulomb’s law states that the force of attraction or repulsion acting between the two charged particles is directly proportional to the product of the magnitude of the two charges and inversely proportional to the square of the distance between them. The force acts on the two particles from a distance; therefore, this is known as a non-contact force. The intensity of the electrical interaction existing between the two charged particles is a vector quantity because it has a distance as well as a magnitude. The direction of the force depends on the polarity possessed by the charges. The charges get attracted towards each other if they are of opposite polarity and get repelled if they are charged with the same polarity.

## Examples

### 1. Mixing Substances in Water

The polarity of a substance plays a very important role in determining its solubility in a solvent. For example, sodium chloride or table salt is polar in nature, which is why it gets attracted to the water and gets dissolved into it easily. On the other hand, oil is non-polar in nature hence, it does not get mixed up with water. There exists an electrostatic interaction between the solute and the solvent. Hence, the presence of the Coulomb’s law can be easily observed.

### 2. Xerox Machine

A Xerox machine consists of a hydrogen lamp, a photosensitive drum, an ink drum, and a mechanism that provides blank papers. The document to be copied is placed upside down on the glass. It is then scanned with the help of a beam of light. The blank portions of the document reflect the light away; whereas, the dark alphabets do not allow the light to bounce back. This reflected light is made to fall on a drum that is electrically charged and is coated with a photosensitive element called selenium. Due to the photosensitive nature, the areas of the drum exposed to a light start behaving as a conductor, and the area not exposed to light remain negatively charged. The drum builds an electrical impression of the document on its surface. Then, it rotates and comes in contact with the toner. The toner is positively charged, hence it gets attracted to the negatively charged parts of the impression. The drum then transfers the image to paper, thereby completing the process of photocopying.

### 3. Charged Rod

A glass rod gets charged when it is rubbed with a specific type of cloth like a silk cloth or a woollen piece of fabric. This charged rod is capable of exerting a force of attraction or repulsion to its nearby objects. For instance, the positively charged bits of paper or light objects like feathers get attracted towards the charged rod. This clearly shows Coulomb’s law in action.

### 4. Balloon Sticking to Wall

When a balloon is rubbed with a piece of cloth, it develops a certain amount of negative charge on its surface. When this negatively charged balloon is brought close to a neutral or positively charged wall, it sticks to it with the help of a force of attraction existing between the two. This complete process works on the basis of Coulomb’s law.

### 5. Comb and Bits of Paper

Charges get deposited on the teeth of a comb when it is rubbed against the hair. The charged comb attracts the bits of paper that are charged with opposite charge or are neutral in nature. The electrical interaction between the paper pieces and the comb is a prominent example of Coulomb’s law.

### 6. Powder Coating

The powder is a mixture of polyester and pigments. The powder is placed in the spray gun and is positively charged with the help of an electromagnetic coil. The object that is to be coated is negatively charged by grounding it with the help of a wire. The Coulomb’s force of attraction existing between the positively charged powder and the negatively charged object allows the paint to get evenly deposited on the surface of the object. It is most commonly used in the automobile industry and for other commercial applications.

### 7. Electrostatic Air Cleansing

They are also known as electrostatic precipitators. An electrostatic air cleaner is capable of ionizing the dust and smoke particles present in the air by making it pass through an electric cell. A collector plate that is charged with opposite polarity is brought in contact with the charged dust and smoke particles, thereby establishing a force of attraction between the two. The magnitude of this force of attraction can be calculated easily with the help of Coulomb’s law. Hence, it is one of the chief applications of Coulomb’s law.

### 8. Styrofoam and Aluminum Plate

When a piece of Styrofoam is rubbed with a wool sock, a layer of negative charges get deposited on its surface. When an aluminium plate is brought close to the Styrofoam sheet, an electric interaction between the two gets formed. On touching the plate, a spark can be seen and felt. This demonstrates the working of Coulomb’s law in real life.