Electric Charge Formula & Examples for Physics Students
Electric charge is a basic property of matter carried by certain elementary particles. This property governs how particles are influenced when they are placed in an electric or magnetic field. Materials or particles can have positive or negative electric charge, and this charge is fundamental to the way matter interacts through electromagnetic forces.
Electric charges always occur in discrete natural units. This means electric charge comes in fixed, smallest possible amounts, and cannot be divided into smaller pieces. The charge carried by a single electron or proton is called the elementary charge, and it is the minimum possible unit of charge observed in nature.
Definition and Nature of Electric Charge
Electric charge can be positive or negative. Objects or particles are positively charged when they have an excess of a certain property (like protons), and negatively charged when they have a deficit (such as extra electrons).
A key aspect of electric charge is that it is neither created nor destroyed. This principle, known as conservation of electric charge, ensures the total charge in a closed system remains constant, no matter what physical or chemical processes occur within the system.
Unit of Electric Charge
The standard unit for measuring electric charge is the coulomb (C). In simple terms, a coulomb represents a known, fixed amount of electric charge. In daily life and experiments, subunits like microcoulombs (μC) or nanocoulombs (nC) are also used.
The elementary charge (usually denoted by e) is the charge of a single proton or electron. This smallest unit is about 1.6 × 10–19 coulombs, providing the natural building block for all electric charge observed.
Core Properties of Electric Charge
- Electric charge can be positive or negative.
- Charge exists in discrete, unbreakable units known as elementary charges.
- The total charge in a closed system always remains constant—charge cannot be created or destroyed.
| Property | Description |
|---|---|
| Discrete units | Electric charge is found only in fixed amounts (elementary charges) |
| Conservation | Total electric charge remains constant within an isolated system |
| Positive or Negative | Can be either type, never both simultaneously on a single particle |
Examples of Electric Charge
Electric charge is a key factor behind physical phenomena like static electricity, where rubbing certain materials transfers electrons and makes them attract or repel each other. For example, rubbing a plastic comb on hair can make the comb attract small paper pieces due to transferred electric charges.
Another common example involves subatomic particles. Protons carry positive charge and electrons carry negative charge. The interaction of these elementary charges results in various forces and effects in atoms, matter, and even in large-scale objects.
Step-by-Step Approach to Electric Charge Calculations
- Identify if the charge in question is positive or negative, and count the number of charges present.
- Multiply the number of elementary charges by the value of e (1.6 × 10–19 C) to determine the total charge.
- If comparing different objects or particles, consider the conservation principle to ensure the total charge remains unchanged after any transfer.
| Formula | Application |
|---|---|
| Q = n × e | Q = total electric charge, n = number of elementary charges, e = 1.6 × 10–19 C |
Practical Example
Suppose an object has gained 5 × 1018 electrons. The total charge on the object will be:
Q = n × e = 5 × 1018 × (–1.6 × 10–19 C) = –0.8 C
The negative sign indicates the object is negatively charged.
Key Points on the Conservation and Quantization of Charge
- Whenever electric charge moves from one place to another, the total amount of charge always stays the same.
- In chemical reactions and physical processes, charge may be transferred but is not created or destroyed.
- All observable electric charge is found in multiples of the elementary charge.
Further Learning and Related Topics
- Electric Current
- Electricity in Physics
- Basic Properties of Electrical Charge
- Force, Work, and Energy
- SI Units list
- Electric Charge and Static Electricity
Summary
Electric charge is an unchanging, fundamental property of matter that is central to many physical phenomena. It occurs in positive and negative forms, always in whole-number multiples of a fixed, elementary value. The conservation of electric charge and its discrete nature are essential principles in physics, chemistry, and engineering.
A strong grasp of electric charge concepts builds a solid foundation for topics like electric current, electrostatics, and electricity and magnetism.
FAQs on Electric Charge: Meaning, Types, Properties & Applications
1. What is electric charge?
Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric or magnetic field. There are two types of electric charges: positive and negative. This property is responsible for various electric and electromagnetic phenomena, and it is carried by particles such as electrons (negative charge) and protons (positive charge).
2. What is the SI unit of electric charge?
The SI unit of electric charge is the coulomb (C). One coulomb is equal to the charge carried by approximately 6.242 × 1018 electrons or protons.
3. What is the formula for electric charge?
The formula for electric charge is:
Q = n × e
Where:
- Q = Total electric charge (in coulombs)
- n = Number of electrons or protons
- e = Elementary charge (1.6 × 10−19 C)
4. What are the properties of electric charge?
The main properties of electric charge are:
- Conservation: Charge cannot be created or destroyed.
- Quantization: Charge exists in discrete units (integral multiples of the elementary charge).
- Additivity: Algebraic sum of individual charges gives the total charge.
- Attraction and Repulsion: Like charges repel; unlike charges attract.
5. What are the types of electric charge?
There are two types of electric charge:
- Positive charge (+): Carried by protons.
- Negative charge (−): Carried by electrons.
6. How is electric charge created or transferred?
Electric charge is transferred by:
- Friction: Rubbing transfers electrons between objects.
- Conduction: Direct contact allows electrons to move from one object to another.
- Induction: Nearby charged object induces redistribution of charges without contact.
7. What is the charge of an electron?
The charge of an electron is −1.6 × 10−19 coulombs (C). The negative sign indicates that it is a negative charge.
8. What is meant by quantization of charge?
Quantization of charge means that charge exists only in discrete packets, i.e., it is always an integral multiple of the elementary charge. Mathematically, Q = n × e, where n is an integer and e = 1.6 × 10−19 C.
9. State the law of conservation of charge.
The law of conservation of charge states that the total electric charge in an isolated system remains constant over time. Charges can be transferred between bodies, but the net charge does not change during any physical or chemical process.
10. What is the difference between electric charge and electric current?
Electric charge is the property of particles responsible for electric phenomena, while electric current is the rate at which charge flows through a conductor.
- Charge is measured in coulombs (C).
- Current is measured in amperes (A), where 1 A = 1 C/s.
11. Give an example of quantization of charge in daily life.
Rubbing a plastic comb on dry hair transfers electrons so the comb becomes negatively charged. The total charge on the comb will always be a whole number multiple of the elementary charge (e), illustrating the quantization of charge.
12. How can we detect the presence of electric charge on a body?
An electroscope is commonly used to detect electric charge. When a charged object is brought near or touched to the metal knob of the electroscope, the leaves diverge, showing the presence of electric charge due to electrostatic repulsion.
