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Meghna Thapar 5 years, 6 months ago
The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg).
Posted by Chhavi Mahajan 5 years, 6 months ago
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Yogita Ingle 5 years, 6 months ago
| Prokaryotes | Eukaryotes | |
| Type of Cell | Always unicellular | Unicellular and multi-cellular |
| Cell size | Ranges in size from 0.2 μm – 2.0 μm in diameter | Size ranges from 10 μm – 100 μm in diameter |
| Cell wall | Usually present; chemically complex in nature | When present, chemically simple in nature |
| Nucleus | Absent | Present |
| Ribosomes | Present. Smaller in size and spherical in shape | Present. Comparatively larger in size and linear in shape |
| DNA arrangement | Circular | Linear |
| Mitochondria | Absent | Present |
| Cytoplasm | Present, but cell organelles absent | Present, cell organelles present |
| Endoplasmic reticulum | Absent | Present |
Posted by Sourav Kumar 5 years, 6 months ago
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Meghna Thapar 5 years, 6 months ago
Chemical Properties of Metals and Non-metals:
- Reaction with oxygen:
Metals react with oxygen to form metal oxides. Metals oxides are basic in nature which turns red litmus to blue. When magnesium burns in air, it combines with oxygen to form magnesium oxide.
ii. Reaction with water:
When a metal reacts with water, then a metal hydroxide and hydrogen gas are formed. The vigour of reaction of metal with water depends on its chemical reactivity. Example – sodium is a very reactive metal so it reacts violently even with cold water.
iii. Reaction with acids: Most of the metals react with dilute acids to form salts and hydrogen gas that burns with a ‘pop’ sound. Only less reactive metals like copper, silver and gold do not react with dilute acids.
Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas.
iv. Reaction with bases:
Some metals react with bases to form salts and hydrogen gas. For example – when aluminium is heated with sodium hydroxide solution, then sodium aluminate and hydrogen gas are formed.
Posted by Anshika Tyagi 5 years, 6 months ago
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Yogita Ingle 5 years, 6 months ago
| Cell Membrane vs Nuclear Membrane | |
| Cell membrane is defined as the cytoplasmic lipid bilayer membrane that surrounds the protoplasm of the cell. | Nuclear membrane is defined as the two lipid bi layer membrane which surrounds the genetic material and nucleolus of the eukaryotic cell. |
| Nature of the Membrane and Pores | |
| Cell membrane is a continuous membrane without any pores. | Nuclear membrane is a discontinuous membrane with complex pores. |
| Number of Units | |
| Cell membrane is a single unit membrane (one lipid bilayer). | Nuclear membrane consists of two unit membranes (two lipid bilayers). |
| Persistence | |
| Cell membrane persists during the lifetime of the cell. | Nuclear membrane disappears during the cell division in prometaphase and reforms again in telophase. |
| Permeability and Transportation | |
| The cell membrane is semi-permeable membrane and regulates the flow of substances like ions, organic molecules between protoplasm and external environment. | The nuclear membrane is permeable only to small non-polar molecules (mRNA and proteins) and regulates the flow of these molecules between nucleoplasm and cytoplasm. |
| Endoplasmic Reticulum (ER) | |
| The endoplasmic reticulum is not found attached to the cell membrane. | The endoplasmic reticulum is normally found attached to the nuclear membrane. |
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Meghna Thapar 5 years, 6 months ago
- We hear Sound through Our Ears:
The ears are the sense organs which help us in hearing. The shape of the outer part of the ear is like a funnel. The outer part of the ear is called pinna which is attached to about 2 to 3 centimetre long passage called ear canal. At the end of the ear canal a thin, elastic and circular membrane called eardrum is stretched tightly. There are three small and delicate bones called hammer, anvil and stirrup in the middle part of the ear which are linked to one another. The inner part of the ear has a coiled tube called cochlea. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we hear.
We should not put anything like pin, pencil or pen inside our ears as they can tear the eardrum and make a person deaf.
Posted by Poonam Rishi 5 years, 6 months ago
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Meghna Thapar 5 years, 6 months ago
A complete octet is very stable because all orbitals will be full. Atoms with greater stability have less energy, so a reaction that increases the stability of the atoms will release energy in the form of heat or light. A stable arrangement is attended when the atom is surrounded by eight electrons.
Posted by Kulsum Kalim 5 years, 6 months ago
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Meghna Thapar 5 years, 3 months ago
The image formed by a plane mirror is always virtual (meaning that the light rays do not actually come from the image), upright, and of the same shape and size as the object it is reflecting. A virtual image is a copy of an object formed at the location from which the light rays appear to come.
The size of the image can be identified by using the magnification formula for the mirror.
For nature of the image, you have to know that a convex mirror forms:
- located behind the convex mirror.
- a virtual image.
- an upright image.
- reduced in size (i.e., smaller than the object)
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Meghna Thapar 5 years, 6 months ago
The chemical decomposition produced by passing an electric current through a conducting liquid is called electrolysis.
Take out carbon rods carefully from two discarded cells. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery. These two rods are electrodes.Now, pour a cupful of water in a glass/plastic bowl and add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting. Immerse the electrodes in this solution. Make sure that the metal caps of the carbon rods are outside the water. Wait for 3-4 minutes. We will see that the bubbles of gases are produced at the two carbon electrodes. The formation of gas bubbles at the two carbon electrodes shows that a chemical change has taken place in water on passing electric current through it.
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We cannot here the screams of bats because the bats produce ultrasonic sounds[sounds above the frequency of 20000 Hz ] which we humans cannot hear. we cannot hear the sound of bats as they produce ultrasonic sound.
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Deepa Devi 5 years, 6 months ago
2Thank You