Jay's Mathematics Classes

📝 Materials: Metals and Non-Metals  Multiple Choice Questions 1. Which of the following is not a metal? (a) copper (b) sulphur (c) aluminium  (d) iron Ans: (b) 2. The substance that will be flattened on beating with a hammer is (a) crystal of iodine  (b) lump of sulphur  (c) piece of coal (d) zinc granule Ans: (d) 3. Materials which can be drawn into wires are called ductile. Which  of the following is not ductile material? (a) silver (b) copper  (c) sulphur  (d) aluminium Ans: (c) 4. Metals are generally hard. Which of the following metals is an  exception and can be cut with a knife? (a) iron  (b) sodium (c) gold (d) magnesium Ans: (b) 5. Metals generally react with dilute acids to produce hydrogen gas.  Which one of the following metals does not react with dilute  hydrochloric acid? (a) magnesium  (b) aluminium (c) iron (d) copper Ans: (d) 6. Which of the following reacts with cold water vigorously? (a) ...

 📝Refraction of Light Refraction of Light.   When a ray of light, propagating (in a straight line) in one transparent medium, enters another transparent medium, it is observed to (usually) change its direction of propagation or bend its path. We call this phenomenon as refraction of light.  Cause of Refraction of Light.  The speed of light is different in different media. In a vacuum, light propagates at a speed of `3 × 10^8 ms^{-1}`, but when it enters any other transparent medium, its speed decreases. It is this change in speed of light, that causes a light ray to bend when it goes from one medium to another. Thus, refraction is basically due to a change in the speed of light when it goes from one medium to another.  Optical Density The speed of light, in a given medium, is taken as an indicator of its optical density. We can say that the more is the speed of light in a given medium, the less is its optical density and vice-versa. Optically denser medium ...

 📝Question Bank Class 8  Mathematics  ● Squares & Square Roots 📝 Science  ● Materials: Metals and Non-metals 📝 ● Combustion & Flame 

 📝Class 8 (Mathematics & Science) Science  Chapters ●  Cell - Structure and Functions  📝 ●  Materials: Metals & Non-Metals  📝 ●  Combustion & Flame  ●  Force & pressure ● Refraction of Light 📝 ●   Reproduction in animals 

 Cell - Structure, and Functions The basic structural unit of an organ, which is the cell . Cells may be compared to bricks. Bricks are assembled to make a building. Similarly, cells are assembled to make the body of every organism. Discovery of the Cell Robert Hooke in 1665 observed slices of cork under a simple magnifying device. Cork is a part of the bark of a tree. He took thin slices of cork and observed them under a microscope. He noticed partitioned boxes or compartments in the cork slice. These boxes appeared like honeycomb.  He also noticed that one box was separated from the other by a wall or partition. Hooke coined the term ‘cell’ for each box. What Hooke observed as boxes or cells in the cork were actually dead cells. Cork Cell The Cell A Cell can be defined as the basic structural and functional unit of all living organisms.  Both, bricks in a building and cells in living organisms, are basic structural units.  The buildings, though built of simi...