ASK Rare Class Notes – Study Resources for Students & Teachers

Class 8 General Science Notes: - Unit-12: Our Universe: C . Long Questions  Q1.  What are galaxies? Explain different types of galaxies? Ans: Galaxies: A galaxy is a huge collection of gases, dust, billions of stars, and their solar system.  Galaxies are classified into three main types. 1. Spiral galaxies. Spiral galaxies are large rotating disks of stars and the central bright region at the core of a galaxy is called the galactic bulge. Example: Our milky way is a spiral galaxy. 2. Elliptical galaxies Elliptical galaxies are roughly egg-shaped and have no galactic bulge at their centers. These galaxies contain old stars as there are few new stars formation occurring in them. They can range in size from a few thousand light-years across to more than a few hundred thousand. 3. Irregular Galaxies Irregular galaxies are irregular in shape. They are in constant motion as a group.   Q.2- How do stars form? What stages does a star pass through? Why do some ...

Class 8 General Science Notes: - Unit-12: Our Universe:  B . Short Questions  i) Why are distances in space often measured in light years? Ans: A light year is a large unit equal to the distance traveled by light in one year. Hence distance in space is very large and measured in light years. ii) Is our sun in motion through space? Ans: Yes, our sun is in motion through space. In fact, our whole solar system orbits around the center of the Milky Way galaxy with an average speed of 828000 km/h. iii) What is the source of the sun’s energy? Ans: The nuclear fusion reaction is the source of the sun’s energy. Fusion occurs when protons of hydrogen atoms violently collide in the sun's core to create a helium atom. iv) Why the sun will not become a black hole? Ans: T he sun would need to be about 20 times more massive to end it as a black hole. A black hole is a region where gravity is so strong that nothing, no particle even light can escape fro...

Class 8 General Science Notes: - Unit-11: Technology in Everyday Life: C . Long Questions  Q1.  What is the spherical mirror type used in the solar cooker? How it can be used to cook food? Ans: In solar cookers, the concave spherical mirror is used. In a concave spherical mirror, the inner surface of the spherical section is made reflecting. A beam of light is directed towards a concave mirror along its principal axis. After reflecting from the mirror, the ray converges to a single point in front of the mirror called the focus point F. By using a concave mirror we can direct the energy in sunlight to a single point. This reflected light is very powerful because it carries a lot of thermal energy. Solar cookers are one of the simplest utensils used to cook food. It harnesses the power of the sun to cook food. Q2. What is a wind turbine? How it is used to produce electricity? Ans: A wind turbine is a large vanned (covered with feathers) whee...

Class 8 General Science Notes: - Unit-11: Technology in Everyday Life:  B . Short Questions  i) What is the most important material in toothpaste? Ans: Alkali is the most important material in toothpaste. So brushing toothpaste  neutralizes the acid which prevents tooth decay. ii) Why does milk turn into plastic when vinegar is added to it? Ans: Milk contains a protein called casein when vinegar (acid) is mixed with milk. Casein molecules combine to form long-chain products called casein plastic or milk plastic. This plastic can be easily molded. iii) What is saponification? Ans: When oil or fats are heated with an alkali Na0H, Sodium salts of fatty acid (Organic acid) are formed. This reaction is known as the saponification reaction. iv) Why it is better to use a concave mirror in a solar cooker? Ans: Concave Mirrors are mirrors whose inner surface of a spherical section is made reflecting. After reflection from the mirror, the rays Converge to a single po...

Class 8 General Science Notes: - Unit-10: Electricity and Magnetism: C . Long Questions  Q1.  What is resistance and in what units do we measure resistance? Ans: Electric Resistance :  Electric resistance is the opposition to the motion of charge through a material. Resistance lowers the flow of current in a circuit. The value of resistance “R” is obtained by dividing the voltage ‘’V” by the current “I” it carries. R = `\ frac {V}{I}` Unit of Resistance :  The unit of resistance is Ohm and is represented by the Greek letter (omega) Ω. The  resistance of a wire is one Ohm if the potential difference of one volt is applied across its  ends and causes a current of one Ampere to flow through it. 1Ω =  `\ frac {1V}{1A}` Q.2- State and explain electric power by giving its mathematical description? Ans: Electric Power :  Electric power is the rate at which electrical energy is used in a  circuit. Mathematical  description of ...