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Ask QuestionPosted by Niharika Raj 5 years, 2 months ago
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Posted by Niharika Raj 5 years, 2 months ago
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Yogita Ingle 5 years, 2 months ago
Rabi crops are known as winter crops. They are grown in October or November. The crops are then harvested in spring. These crops require frequent irrigation because these are grown in dry areas. Wheat, gram, barley are some of the rabi crops grown in India.
Examples of Rabi Crops
Following are some of the examples of rabi crops:
- Wheat
- Barley
- Oats
- Pulses
- Mustard
- Linseed
Posted by Muskan Shekhawat 5 years, 2 months ago
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Yogita Ingle 5 years, 2 months ago
Hari Singh was 15 years old, but already he was an experienced and fairly successful thief.
He used to change his name frequently so as not to get caught by his former employees, whom he must have cheated.
He even cheated Anil when he went to buy the daily supplies of groceries. However , he wished to get an education so that he could become a big and respected man, who would be able to achieve a lot.
He stole a large sum of money from Anil but regretted it when he realised that in doing so he had lost his only chance of getting an education. He is courageous enough to return the money , even though he knows that he may be caught in the process.
However his desire to change himself is so great that it motivates him and gives him courage to return to Anil.
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Gaurav Seth 5 years, 2 months ago
Electric Motor
Electric Motor is a device which converts electrical energy into mechanical energy.
Principle of Electric Motor
The principle of the electric motor is based on the fact that a current carrying conductor produces a magnetic field around it. A current carrying conductor placed perpendicular to magnetic field experiences a force.
Construction of Electric Motor
(1) Armature coil
It consist of a single loop of an insulated copper wire in the form of a rectangle.
(2) Strong field magnet
Armature coil is placed between 2 pole pieces of a strong magnet which provide strong magnetic field.
(3) Split ring type commutator
It consist of 2 halves of a metallic ring.The two ends of armature coil are connected to these 2 halves of ring.Commutators reverses the direction of current in armature coil.
(4) Brushes
Two carbon brushes press against the commutator.These brushes act as contact between commutator and terminal battery.
(5) Battery
It is connected across the carbon brushes.It supplies current to the armature coil.
Working of Electric Motor
1)In the side AB of the rectangular cil ABCD, the direction of current is from A to B and in the side CD of the coil, the direction of current is from C to D.The direction of magnetic field is from N pole of the magnet to its S pole.
2) Applying Fleming’s Left hand rule to sides AB and CD of the coil, the force on side AB of the coil is in downward direction whereas the force on side CD of the coil is in upward direction. Due to this the side AB of the coil is pushed down and side CD is pushed up.This makes the coil ABCD rotate in the anticlockwise direction.
3) While rotating, when the coil reached vertical position, then the brushes will touch the gap between the two commutator rings and current of the coil is cut off. Though the current to the coil is cut off when it is in the exact vertical position, the coil does not stop rotating because it has already gained momentum due to which it goes beyond the vertical position.
4) After half rotation, when the coil goes beyond vertical position, the side CD of the coil comes on the left side whereas side AB of the coil comes to the right side, and the two commutator half rings automatically change contact from one brush to the other.
5) After half rotation of the coil , the commutator half ring R2 makes contact with brush B1 whereas the commutator half ring R1 makes contact with brush B2.This reverse the direction of current in the coil.
6) The reversal of direction of current reverses the direction of force acting on the sides AB and CD of the coil.The side CD of the coil is now on the left side with a downward force on it whereas the side AB is now on the right side with an upward force on it.Due to this the side CD of the coil is pushed down and the side AB of coil is pushed up.This makes the coil rotate anticlockwise by another half rotation.
7) The reversing of current in the coil is repeated after every half rotation due to which the coil continue to rotate as long as current from the battery is passed through it.
Posted by Saloni Priya 5 years, 2 months ago
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Yogita Ingle 5 years, 2 months ago
The chemical properties of metals.
- The density of metals is usually high.
- Metals are malleable and ductile.
- Metals form an alloy with other metals or non – metals.
- Some metals react with air and corrode. For e.g. Iron.
- Metals are good conductors of heat and electricity. Lead is an exception.
- Generally, metals are in a solid state at room temperature. Except for Mercury. Mercury is in a liquid state.
The chemical properties of nonmetals
- Nonmetals are poor conductors of heat and electricity. Graphite and Gas carbon are exceptions.
- Unlike metals, nonmetals aren’t malleable and ductile.
- Nonmetals react more with metals than with nonmetals.
- Usually, nonmetals react with other nonmetals in high temperature.
- Most nonmetals do not react with air in room temperature.
- White phosphorus is the only nonmetal that reacts with air to form its oxide by burning.
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Yogita Ingle 5 years, 2 months ago
Full-fledged territorial state means a country which is independent and is a sovereign state. In early modern period, a full fledged state meant a country which had clear boundaries, was independent and was not under the rule of any country. It may be however, under a monarchy.
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Diksha Patel 5 years, 2 months ago
Yogita Ingle 5 years, 2 months ago
Limitations of Dobereiner’s classification of elements was that it failed to arrange all the then known elements in the form of triads of elements having similar chemical properties. His classification was not applicable to all known elements but was limited only to a few elements. For example: nitrogen, Phosphorus and arsenic have similar chemical properties but they do not constituent a Dobereiner’s triad. Dobereiner’s could identify only three triads from the elements known at that time. So his classification of elements was not much successful. Dobereiner also failed to explain the relation between atomic masses of elements and their chemical properties.
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Yogita Ingle 5 years, 2 months ago
Mercury is obtained from its sulphide ore called cinnabar, HgS which is actually mercury(ii) sulphide.
The following steps are involved in its extraction:
1. mercury ore is roasted
2HgS(s) + 3 O2 (g) -----> 2HgO (s ) + 2 SO2 (g)
2. when this mercury oxide is heated at about 300 degrees Celsius , it decomposes to form mercury metal.
2HgO (s) ------> 2Hg (l) + O2(g)
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Yogita Ingle 5 years, 2 months ago
Zaid Crop: These are crops which are sown between the rabi and kharif crops. Watermelon, muskmelon, cucumber and vegetables are some examples of the zaid crops.
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