The alchemist edusys

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Corona special

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Only for the best

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Class 10

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Hurrry.....

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Satya

11/08/2015

These are common and trivial names of the most important chemical compounds every one of you must know them as they are important.

06/08/2015

Dimensions trick for jee
Dimensional analysis of the answers
Dimensional analysis is very handy in almost all the entrance examinations. You will even get questions from IIT JEE which can be solved by using this trick. This is not a short cut; it’s what you learnt in the first Chapter of Physics in Plus one. The method is very easy and can be applied in Physics and Chemistry questions; Let us understand it with an example.

Q. A highly rigid cubical block A of small mass M and side L is fixed rigidly onto another cubical block B of the same dimensions and of low modulus of rigidity ɳ such that the lower face of A completely covers the upper face of B. The lower face of B is rigidly held on a horizontal surface. A small force F is applied perpendicular to one of the side faces of A. After the force is withdrawn, block A executes a small oscillation. The time period of oscillation is: (IIT JEE 1992)
(a)2π MɳL (b) 2π Mɳ/L
(c) 2π ML/ɳ (d) 2π M/ɳL
Sol:
How’s the question? A little bit lengthy and tougher? How should it be when it’s an IIT JEE question? But the question is not that much tough if you are going in the indirect method. And often the bright students will use these indirect steps first before doing the direct method.
What’s the indirect method? It’s none other than dimensional analysis. Please read the last sentence of question. We are asked to find out the time period of oscillation. The dimensional formula of Time period or time is [T]. So the dimension of our answer should be [T].
You need to know the dimension of other given information in the problem. The dimension of Mass M is [M] and length L is [L] . Some of you may find it difficult to find the dimension of modulus of rigidity ɳ . But it’s very easy to find if you know what modulus of rigidity is. I will tell the direct formula here;
Modulus of rigidity, ɳ =-F/lx
Therefore dimensional formula of ɳ =[MLT^-2]/[L][L] =[ML^-1 T^-2]
Now check for the dimension of Time period in each option. Let us take the first option. The final dimensional formula of that answer comes to be [MT^-1].
Option (b) comes out to be [ML^-1 T^-1]
Option (c ) comes out to be [LT]
Now check option (d). It’s [M]/[ ɳ ][L]
= [M]/[ML^-1 T^-2][L]
= [T]
How’s it? You can solve lots of questions like this in many entrance examinations. To solve problems like this, you should need some practice with these types of questions. Take some previous years’ question papers and solve. You will definitely find questions like this.

04/08/2015

Here is Shortcut trick to find cube root of a number quickly in seconds:
The main point is to memorize the cubes of 1 to 9 and remember their unit’s place number. These will help in solving the cube roots of a number. Here is the table of cubes of number up to 9 for your convenience.
Table of cubes of numbers up to 9.
1 –> 1
2 –> 8
3 –> 27
4 –> 64
5 –> 125
6 –> 216
7 –> 343
8 –> 512
9 –> 729
Since you have remembered the cubes of first 9 natural numbers and their unit digits, now you can easily calculate cube root of numbers quickly and easily.
Below is an example.
Find the cube root of 474552?
Solution:
step 1. Divide the number in 2 parts i.e. 474 (first part) and 552 (second part) starting from right side of given number. (if there are 5 digits in given number, then we will divide it as last 3 numbers as 1st part and starting 2 numbers as part 2)
Step 2. find the largest cube contained in the first part but that cube should be smaller than the first part (nearest smaller or equal) i.e. 474’s nearest cube which is smaller than 474 is cube of 7=343. Now ten’s part of cube root of 474552 is 7.
Step 3. Now take part second. See the last digit of the 2nd part and match it with table to see which number’s cube had 2 as the last digit (unit place digit). Since 512 is the number which has 2 in its unit’s place and 512 is cube of 8. Hence 8 is the number which should be at unit’s place.
So our cube root of number 474552 becomes 78.
Let us take another example.
Calculate the cube root of 17576.
Here is the solution to the above problem.
Step 1. Divide in two parts i.e. 17 (1st part- it will determine ten’s place)and 576 (it will determine unit’s place).
Step 2. In first part, the largest cube less than 17 is 8 (which is cube of 2). So, ten’s digit of the cube root of 17576 is 2.
Step 3. In Part 2, the ending digit is 6. Hence, unit’s digit is 6. So, unit’s digit of the cube root of 17576 is 6.
So putting ten’s digit and unit’s digit together, we get 26 as the answer.
You should practice this cube root shortcut trick with just a bit of practice you can easily solve cube root of numbers quickly in seconds.
Now practice by yourself the above given cube root shortcut trick and find the answer to the following questions.
Find the cube root of the following numbers:
1. 42875
2. 238328
3. 3375
4. 373248

If you have learned the cube root shortcut trick (how to find cube root of numbers quickly), then POST YOUR ANSWER IN THE COMMENTS by solving through above given trick and then match it using normal calculation.