What are conservation laws in physics class 12?
2 Answers
In physics, conservation laws are fundamental principles that describe how certain quantities remain constant in isolated systems as they evolve over time. In the context of Class 12 physics, the main conservation laws typically covered include:
### 1. **Conservation of Energy**
This law states that the total energy in an isolated system remains constant over time. Energy can neither be created nor destroyed; it can only be transformed from one form to another. For example, potential energy can convert into kinetic energy and vice versa, but the total amount of energy remains the same. This principle underpins much of classical mechanics and is crucial in various applications, from simple pendulums to complex systems.
**Mathematical Expression:**
\[ E_{\text{total}} = E_{\text{kinetic}} + E_{\text{potential}} = \text{constant} \]
### 2. **Conservation of Momentum**
Momentum is conserved in an isolated system where no external forces are acting. Momentum is defined as the product of mass and velocity. The total momentum before and after an event, such as a collision or explosion, remains the same.
**Mathematical Expression:**
\[ \text{Total Momentum}_{\text{before}} = \text{Total Momentum}_{\text{after}} \]
\[ m_1 \cdot v_1 + m_2 \cdot v_2 = m_1 \cdot v_1' + m_2 \cdot v_2' \]
where \( m_1 \) and \( m_2 \) are masses, and \( v_1 \) and \( v_2 \) are their respective velocities before the event; \( v_1' \) and \( v_2' \) are their velocities after the event.
### 3. **Conservation of Angular Momentum**
Angular momentum is conserved in a system where no external torques are acting. This law states that if the net external torque on a system is zero, the total angular momentum of the system remains constant.
**Mathematical Expression:**
\[ L_{\text{total}} = I \cdot \omega = \text{constant} \]
where \( I \) is the moment of inertia, and \( \omega \) is the angular velocity.
### 4. **Conservation of Charge**
The total electric charge in an isolated system remains constant over time. This principle is fundamental in electromagnetism and ensures that charge is neither created nor destroyed in physical processes.
**Mathematical Expression:**
\[ Q_{\text{total}} = \text{constant} \]
where \( Q \) represents electric charge.
### Examples and Applications:
- **Conservation of Energy:** In a roller coaster, the sum of kinetic and potential energy remains constant, neglecting friction.
- **Conservation of Momentum:** When two ice skaters push off each other, they move in opposite directions with equal and opposite momenta.
- **Conservation of Angular Momentum:** A figure skater spins faster by pulling their arms in close to their body.
- **Conservation of Charge:** In a closed circuit, the total charge flowing through the circuit remains constant.
These laws are foundational concepts in physics and are crucial for understanding a wide range of physical phenomena and solving problems in classical mechanics, electromagnetism, and beyond.
### 1. **Conservation of Energy**
This law states that the total energy in an isolated system remains constant over time. Energy can neither be created nor destroyed; it can only be transformed from one form to another. For example, potential energy can convert into kinetic energy and vice versa, but the total amount of energy remains the same. This principle underpins much of classical mechanics and is crucial in various applications, from simple pendulums to complex systems.
**Mathematical Expression:**
\[ E_{\text{total}} = E_{\text{kinetic}} + E_{\text{potential}} = \text{constant} \]
### 2. **Conservation of Momentum**
Momentum is conserved in an isolated system where no external forces are acting. Momentum is defined as the product of mass and velocity. The total momentum before and after an event, such as a collision or explosion, remains the same.
**Mathematical Expression:**
\[ \text{Total Momentum}_{\text{before}} = \text{Total Momentum}_{\text{after}} \]
\[ m_1 \cdot v_1 + m_2 \cdot v_2 = m_1 \cdot v_1' + m_2 \cdot v_2' \]
where \( m_1 \) and \( m_2 \) are masses, and \( v_1 \) and \( v_2 \) are their respective velocities before the event; \( v_1' \) and \( v_2' \) are their velocities after the event.
### 3. **Conservation of Angular Momentum**
Angular momentum is conserved in a system where no external torques are acting. This law states that if the net external torque on a system is zero, the total angular momentum of the system remains constant.
**Mathematical Expression:**
\[ L_{\text{total}} = I \cdot \omega = \text{constant} \]
where \( I \) is the moment of inertia, and \( \omega \) is the angular velocity.
### 4. **Conservation of Charge**
The total electric charge in an isolated system remains constant over time. This principle is fundamental in electromagnetism and ensures that charge is neither created nor destroyed in physical processes.
**Mathematical Expression:**
\[ Q_{\text{total}} = \text{constant} \]
where \( Q \) represents electric charge.
### Examples and Applications:
- **Conservation of Energy:** In a roller coaster, the sum of kinetic and potential energy remains constant, neglecting friction.
- **Conservation of Momentum:** When two ice skaters push off each other, they move in opposite directions with equal and opposite momenta.
- **Conservation of Angular Momentum:** A figure skater spins faster by pulling their arms in close to their body.
- **Conservation of Charge:** In a closed circuit, the total charge flowing through the circuit remains constant.
These laws are foundational concepts in physics and are crucial for understanding a wide range of physical phenomena and solving problems in classical mechanics, electromagnetism, and beyond.
In physics, conservation laws are fundamental principles that describe the constancy of certain physical quantities in a closed system, regardless of the processes happening inside the system. For **Class 12** physics, these laws are crucial because they provide the basis for understanding various physical phenomena. Here's a breakdown of the key conservation laws you typically learn at this level:
### 1. **Law of Conservation of Energy**:
- **Statement**: Energy cannot be created or destroyed; it can only be transformed from one form to another. The total energy of an isolated system remains constant.
- **Example**: When a ball is thrown up, its kinetic energy (due to motion) gets converted to potential energy (due to height), and vice versa, but the total energy remains the same.
### 2. **Law of Conservation of Momentum**:
- **Statement**: The total momentum of an isolated system of interacting particles remains constant if no external forces act on it.
- **Momentum** is the product of an object's mass and velocity.
- **Example**: In collisions (whether elastic or inelastic), the total momentum of the system before and after the collision remains the same if no external force is involved.
### 3. **Law of Conservation of Angular Momentum**:
- **Statement**: If no external torque acts on a system, the total angular momentum of the system remains constant.
- **Angular momentum** is a rotational equivalent of linear momentum, given by the product of the moment of inertia and angular velocity.
- **Example**: A figure skater spinning faster when they pull in their arms (decreasing their moment of inertia) demonstrates conservation of angular momentum.
### 4. **Law of Conservation of Charge**:
- **Statement**: The total electric charge in an isolated system remains constant. Charge can neither be created nor destroyed, but can move from one object to another.
- **Example**: When you rub a balloon on your hair, electrons are transferred from your hair to the balloon. The total charge remains the same, but is redistributed.
### 5. **Law of Conservation of Mass (In Classical Physics)**:
- **Statement**: Mass is neither created nor destroyed in an isolated system. This is valid for chemical reactions or processes that don't involve nuclear reactions.
- **Example**: In chemical reactions, the mass of the reactants equals the mass of the products.
### Importance of Conservation Laws:
- These laws help explain interactions in mechanics, thermodynamics, and electromagnetism.
- They provide a way to solve complex problems in physics by simplifying the system analysis. For example, in many collision problems, the law of conservation of momentum helps avoid detailed force calculations.
In summary, conservation laws are powerful tools in physics because they apply universally to a wide range of physical systems and processes, from simple collisions to complex interactions in fields like electromagnetism and quantum mechanics.
### 1. **Law of Conservation of Energy**:
- **Statement**: Energy cannot be created or destroyed; it can only be transformed from one form to another. The total energy of an isolated system remains constant.
- **Example**: When a ball is thrown up, its kinetic energy (due to motion) gets converted to potential energy (due to height), and vice versa, but the total energy remains the same.
### 2. **Law of Conservation of Momentum**:
- **Statement**: The total momentum of an isolated system of interacting particles remains constant if no external forces act on it.
- **Momentum** is the product of an object's mass and velocity.
- **Example**: In collisions (whether elastic or inelastic), the total momentum of the system before and after the collision remains the same if no external force is involved.
### 3. **Law of Conservation of Angular Momentum**:
- **Statement**: If no external torque acts on a system, the total angular momentum of the system remains constant.
- **Angular momentum** is a rotational equivalent of linear momentum, given by the product of the moment of inertia and angular velocity.
- **Example**: A figure skater spinning faster when they pull in their arms (decreasing their moment of inertia) demonstrates conservation of angular momentum.
### 4. **Law of Conservation of Charge**:
- **Statement**: The total electric charge in an isolated system remains constant. Charge can neither be created nor destroyed, but can move from one object to another.
- **Example**: When you rub a balloon on your hair, electrons are transferred from your hair to the balloon. The total charge remains the same, but is redistributed.
### 5. **Law of Conservation of Mass (In Classical Physics)**:
- **Statement**: Mass is neither created nor destroyed in an isolated system. This is valid for chemical reactions or processes that don't involve nuclear reactions.
- **Example**: In chemical reactions, the mass of the reactants equals the mass of the products.
### Importance of Conservation Laws:
- These laws help explain interactions in mechanics, thermodynamics, and electromagnetism.
- They provide a way to solve complex problems in physics by simplifying the system analysis. For example, in many collision problems, the law of conservation of momentum helps avoid detailed force calculations.
In summary, conservation laws are powerful tools in physics because they apply universally to a wide range of physical systems and processes, from simple collisions to complex interactions in fields like electromagnetism and quantum mechanics.