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Meghna Thapar 6 years, 1 month ago
A conduction tester is a device used to determine whether a substance is a good or poor conductor of electricity
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Yogita Ingle 6 years, 1 month ago
*** Hormone- These are chemical substances produced by the *** organs of males and females.examples- Testosterone is a male *** hormone produced by the testis and estrogen is a female *** hormone produced by the ovary.
Functions of *** hormones-
- The female hormone or estrogen which causes development of breasts or mammary glands. Milk on which new born babies feed develops inside the these mammary glands. It also causes the development of *** organs.
- The male hormone testosterone brings about secondary sexual characters such as the growth of beard, hairs on the skin, development of *** organs.
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Greenhouse effect may lead to global warming, i.e., an overall increase in the average temperature of the Earth. Greenhouse effect is caused by greenhouse gases. Examples of greenhouse gases include carbon dioxide, methane and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed by earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus, helps in human survival. However, an indiscriminate increase in the amount of greenhouse gases can lead to excessive increase in the Earth’s temperature leading to global warming.
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Flame is a region where combustion or burning of a gaseous substance takes place. Only the solid or liquids which form gases when heated burn with a flame. Some of the substances which burn by producing flames are LPG, biogas, candle wax, camphor, magnesium and mustard oil.
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The process of depositing a thin layer of desired metal over a metal object with the help of electric current is called electroplating. The purpose of electroplating is to protect the metal objects from corrosion or to make the metal objects look more attractive. The metal objects are usually electroplated with chromium, tin, nickel, silver, gold or copper objects.
Take 250 ml of distilled water in a clean beaker and dissolve two teaspoon full of copper sulphate in it. This will give us a blue coloured copper solution. Add a few drops of dilute sulphuric acid to copper sulphate solution to make it more conducting. Take a copper plate and a door key made of iron. Clean copper plates and the iron key by rubbing it with sand paper. Now rinse them with water and dry them. Immerse the cleaned copper plate in copper sulphate solution in the beaker. Connect the copper plate to the positive terminal of a battery through a switch. This copper plate becomes the positive terminal. Immerse the cleaned iron key in copper sulphate solution and connect it to the negative terminal of the battery so that it becomes the negative electrode. Allow the current to pass for about 15 minutes. Now remove the electrodes from the solution and observe. We will find that the copper plate has dissolved a little and the iron key has got a reddish layer of copper metal all over its surface. Thus, the iron key has become electroplated with copper. The solution remains unchanged.
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Meghna Thapar 6 years, 1 month ago
- Position of Elements in the Periodic Table:
Periods:
The horizontal rows in the Modern Periodic Table are called periods.
The Modern Periodic Table consists of seven periods which are numbered from 1 to 7.
In each period, a new shell starts filling up. The period number is also the number of shell which starts filling up.
The elements in a period have consecutive atomic numbers, and the number of elements in each period is given below:
- First period contains 2 elements and is called a very short period.
- Second and third periods contain 8 elements and are called as short periods.
- Fourth and fifth periods are long periods and contain 18 elements each.
- Sixth period is the longest and contains 32 elements.
- Seventh period is an incomplete period.
Characteristics:
- The elements in a period have consecutive atomic numbers.
- The no. of elements in period is fixed by the maximum no. of electrons which can be accommodated in various shells.
Groups:
- The vertical columns are called groups and consist of eighteen groups numbered from 1 to 18.
- Elements having the same number of valence electrons are present in the same group.
- Elements present in the same group show the same chemical properties.
- Group 1 contains alkali metals and these elements contain 1 electron in their outermost shell.
- Group 2 contains alkaline earth metals and these elements contain 2 electrons in their outermost shell.
- Groups 3 to 12 have their two outermost shells incomplete.
- Groups 13 to 18 group contain 3 to 8 electrons in their outermost shell.
- Group 18 elements have complete outermost shells. So they are called noble elements or noble gases.
- The element hydrogen has been placed at the top of group 1 because its electronic configuration is similar to alkali metals.
Characteristics:
- The elements in a group do not have consecutive atomic numbers.
- All the elements in a group have similar electronic configurations and show similar properties.
Posted by Gaurav Nawariya 6 years, 1 month ago
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Meghna Thapar 6 years, 1 month ago
- Limitations of Mendeleev’s Periodic Table:
- Hydrogen resembles alkali metals as well as halogens. So, a correct position could not be assigned to hydrogen in the periodic table.
- The position of isotopes could not be explained. Isotopes are atoms of the same element having similar chemical properties but different atomic masses. If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the periodic table.
- At certain places, an element of higher atomic mass was placed before an element of lower atomic mass. For example: Cobalt (Co = 58.93) was placed before nickel (Ni =58.71).
- Some elements placed in the same sub group had different properties. For example: Manganese is placed with the halogens which are totally different in their properties.
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Yogita Ingle 6 years, 1 month ago
The number of oscillations per second is known as the frequency of oscillation. Its unit is hertz and is denoted by Hz. The frequency of a wave in general means how frequently the particles of a medium vibrate when a wave moves through the medium.
Posted by Life With Fun 6 years, 1 month ago
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Yogita Ingle 6 years, 1 month ago
- It is a device used in building during construction to protect the buildings from the effect of lightning.
- A metallic rod is erected along the walls of the building during construction such that the tip is protruding outwards at the top of the building.
- The top end is in air and is not in touch with any metallic surface.
- The other end is buried in the ground.
- When a lightning strikes, this provides a direct path for the charges to discharge to the ground, thereby not affecting anybody.
Posted by Ibrahim Khan 6 years, 1 month ago
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Yogita Ingle 6 years, 1 month ago
The efficiency with which the fuel does this conversion of energy is known as fuel efficiency. Now let us take a look at how we measure this fuel efficiency. Fuel efficiency is measured as the amount of heat that 1 kg of fuel (any fuel) produces on combustion. This is known as the calorific value of the fuel.
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Kundan Sharma 6 years, 1 month ago
1Thank You