Electric Charge: Videos & Practice Problems

Electric charge is a fundamental property of matter, present in protons (positive charge) and electrons (negative charge), while neutrons carry no charge. The net charge of an object is determined by the imbalance between protons and electrons. The smallest unit of charge is the elementary charge, denoted as $e=1.610-19C$. Charge quantization means charges exist in integer multiples of $e$. Most objects are electrically neutral, with equal numbers of protons and electrons.

Electric Charge

Electric charge is a fundamental property of matter, similar to mass, and is essential for understanding various concepts in physics. Atoms consist of protons, neutrons, and electrons, where protons and electrons possess electric charge, while neutrons do not. The electric charge can be either positive or negative, with protons carrying a positive charge denoted as \( +e \) and electrons carrying a negative charge denoted as \( -e \). The elementary charge, represented by \( e \), is the smallest unit of charge, approximately equal to \( 1.6 \times 10^{-19} \) coulombs (C).

The net charge of an object is determined by the imbalance between the number of protons and electrons it contains. For example, if an atom has 2 protons and 2 electrons, the net charge is zero, indicating electrical neutrality. Conversely, if an atom has 4 protons and 3 electrons, the net charge would be \( +e \) due to the excess proton. Similarly, an atom with 2 protons and 4 electrons would have a net charge of \( -2e \), reflecting the excess electrons.

It is important to note that neutrons do not contribute to the charge, as they have zero charge. The concept of charge quantization states that electric charge exists in discrete amounts, specifically integer multiples of the elementary charge \( e \). This means that charges cannot be fractional; they must be whole numbers of \( e \).

To calculate the total charge of an object, one can use the formula:

\( Q = n_p \cdot e - n_e \cdot e \)

where \( n_p \) is the number of protons and \( n_e \) is the number of electrons. This equation highlights the relationship between the number of protons and electrons in determining the overall charge of an object.

In most cases, materials are electrically neutral, meaning the number of protons equals the number of electrons, resulting in a net charge of zero. Therefore, unless specified otherwise, it is safe to assume that objects are electrically neutral.

How many electrons make up −1.5 × 10⁻⁵ C?

• A. 9.375×10¹³
• B. 2.4×10⁻²⁴
• C. 1.5×10¹⁴
• D. 9.375×10⁻²⁵

Answer: (A)

How many electrons do you have to add to decrease the charge of an object by 16 μC?

• A. 1.0×10^-25
• B. 1.0×10¹³
• C. 1.0×10¹⁴
• D. 1.0×10¹⁷

Answer: (C)

Here’s what students ask on this topic:

What is electric charge and how is it related to protons, neutrons, and electrons?

Electric charge is a fundamental property of matter that is present in protons and electrons, while neutrons carry no charge. Protons have a positive charge, electrons have a negative charge, and neutrons are neutral. The net charge of an object is determined by the imbalance between the number of protons and electrons. If the number of protons equals the number of electrons, the object is electrically neutral. The smallest unit of charge is the elementary charge, denoted as e, which is approximately 1.6 × 10^-19 C.

What is the elementary charge and its significance in electric charge quantization?

The elementary charge, denoted as e, is the smallest unit of electric charge and is approximately 1.6 × 10^-19 C. It is significant because it represents the charge of a single proton or electron. Charge quantization means that electric charges exist in integer multiples of the elementary charge. This implies that you cannot have a fraction of an elementary charge; charges must be whole multiples of e, such as 0, ±e, ±2e, etc.

How do you calculate the net charge of an object?

To calculate the net charge of an object, you need to determine the imbalance between the number of protons (n_p) and electrons (n_e). The net charge (Q) can be calculated using the formula:

$Q=(n$_p-n_e)×e

Here, e is the elementary charge (1.6 × 10^-19 C). By counting the number of protons and electrons and applying this formula, you can determine the net charge of the object.

What is the difference between positive and negative electric charges?

Positive and negative electric charges refer to the type of charge carried by protons and electrons, respectively. Protons have a positive charge, denoted as +e, while electrons have a negative charge, denoted as -e. The interaction between these charges follows the principle that like charges repel each other, and opposite charges attract each other. This means that two positive charges or two negative charges will repel, while a positive charge and a negative charge will attract each other.

Why are most objects electrically neutral?

Most objects are electrically neutral because they contain an equal number of protons and electrons. This balance means that the positive charges from the protons cancel out the negative charges from the electrons, resulting in a net charge of zero. In everyday materials, this neutrality is common because it is energetically favorable for objects to have no net charge, minimizing the electric forces that would otherwise cause repulsion or attraction between objects.