Prepare for physics excellence with our specialized ‘Class 9 Physics Notes”.
Customized for the curriculum, these notes comprehensively address essential concepts and exam patterns, establishing themselves as your primary resource for thorough preparation. Within, discover succinct responses to paper questions, accompanied by diagrams enhancing your comprehension.
Short Answer Questions.
(a) Define Circular Motion.
Answer. Circular motion is the movement of an object along a curved path. It involves continuous changes in direction, with centripetal acceleration directed toward the center of the circle. Examples include objects in orbit or vehicles navigating curves.
(b) Define Inertia.
Answer. Inertia is the tendency of an object to resist changes in its state of motion. It is a property of matter related to its mass, and according to Newton’s First Law of Motion, an object at rest stays at rest, and an object in motion continues in motion with the same speed and in the same direction unless acted upon by a net external force.
(c) Define Convection.
Answer. Convection is a mode of heat transfer in which heat is transferred through a fluid (liquid or gas) by the movement of the fluid itself. As the fluid is heated, its particles become less dense, rise, and are replaced by cooler, denser particles. This creates a continuous circulation of fluid, facilitating the transfer of heat. Convection is commonly observed in processes such as boiling water or the circulation of air in a room.
(d) Write Name and Symbols of 7 basic units.
Answer. Name and Symbols of 7 basic units.
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Meter (m): The unit of length.
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Kilogram (kg): The unit of mass.
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Second (s): The unit of time.
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Ampere (A): The unit of electric current.
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Kelvin (K): The unit of temperature.
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Mole (mol): The unit of amount of substance.
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Candela (cd): The unit of luminous intensity.
(e) Define Thermal Equilibrium.
Answer. Thermal equilibrium is a state in which two or more objects or systems are at the same temperature and there is no net flow of heat between them. In this state, the thermal energies of the systems are equal, and there is no tendency for heat to move from one system to the other. It is a fundamental concept in thermodynamics, indicating a balance in thermal conditions.
(f) Define Stress.
Answer. Stress is a measure of the internal resistance of a material to deformation when subjected to an external force. It is defined as the force applied per unit area and is expressed in units of pressure (such as pascals or newtons per square meter). Stress plays a crucial role in understanding the mechanical behavior of materials under various conditions.
(g) Define Fossils Fuel.
Answer. Fossil fuels are hydrocarbons, primarily coal, fuel oil, or natural gas, formed from the remains of dead plants and animals over millions of years. These fuels are considered non-renewable energy sources and are extensively used for power generation, heating, and transportation. The burning of fossil fuels releases carbon dioxide and contributes to environmental concerns, including climate change.
(h) Define Wind Energy.
Answer. Wind energy is a renewable energy source that harnesses the kinetic energy of the wind to generate electricity. Wind turbines, equipped with blades that capture the wind’s energy, convert it into mechanical power. This power is then transformed into electrical energy by a generator. Wind energy is environmentally friendly and helps reduce reliance on non-renewable energy sources, contributing to sustainable power generation.
(i) Define Fission.
Answer. Fission is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy. This process is often accompanied by the emission of neutrons and is the fundamental principle behind nuclear power plants and nuclear weapons. Fission reactions release a significant amount of energy and are key to both peaceful and destructive applications of nuclear technology.
(j) Define Physical Quantities.
Answer. Physical quantities are measurable properties or characteristics of a physical system that can be expressed in terms of numbers and units. These quantities can be classified into two types: scalar and vector. Scalar quantities, like mass and temperature, have only magnitude, while vector quantities, such as velocity and force, have both magnitude and direction. Physical quantities are essential in describing the various aspects of the physical world and are subject to measurement and quantitative analysis in the field of physics and other sciences.
(k) Define Non- Conductor.
Answer. A Non-conductor, also known as an insulator, is a material that does not easily allow the flow of electric current. These materials have high electrical resistivity, meaning that they strongly resist the movement of electric charges. Examples of non-conductors include rubber, glass, wood, and plastic. Non-conductors are often used to insulate electrical wires and components to prevent the unintended flow of electricity and ensure the safety of electrical systems.
(l) Define Young’s Modulus.
Answer. Young’s Modulus, also known as the elastic modulus or modulus of elasticity, is a measure of the stiffness of a material. It quantifies the extent to which a material deforms under an applied force. Specifically, Young’s Modulus is defined as the ratio of stress to strain within the elastic limit of a material.
Mathematically, it is expressed as:
Young’s Modulus “Y” = Stress / Strain.
The unit of Young’s Modulus in the International System of Units (SI) is Pascal (Pa) or Newton per square meter (N/m²).
(m) Define Fahrenheit Scale.
Answer. The Fahrenheit scale is a temperature scale commonly used in the United States and a few other countries for everyday applications. On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit (°F), and the boiling point is 212°F, under standard atmospheric pressure. The Fahrenheit scale is based on a mixture of historical and arbitrary references, with 180 degrees between the freezing and boiling points of water. It is less commonly used in scientific contexts compared to the Celsius (Centigrade) and Kelvin scales.
(n) Define Tension in String.
Answer. Tension in a string is the force exerted by the string when it is pulled taut by forces acting on its ends. It is a pulling force transmitted through the string’s length and is always directed along the length of the string. Tension is uniform throughout an idealized massless and flexible string. In the context of physics and mechanics, tension is a crucial concept, often encountered in scenarios involving the equilibrium of objects connected by strings or in the analysis of forces in various mechanical systems.
