
A length scale depends on the permittivity of a dielectric material, Boltzmann constant , the absolute temperature , the number per unit volume of certain charged particles and the charge carried by each of the particles. Which of the following expression(s) for is (are) dimensionally correct?
This question has multiple correct options.
A)
B)
C)
D)
Answer
149.4k+ views
Hint: The dimension of is . So, find the dimensions of RHS of all the options and match with that of the length. You have to find out the dimensions of and . Option A and B are reciprocal of each other so they can’t be correct simultaneously. Similarly, in option C and D, the raised power of is different so they also can’t be correct simultaneously.
Complete step by step answer:
As this question has multiple correct options. So, the best way to solve it to eliminate the incorrect options or to check all the options.
We know that the dimension of is , so we have to find the dimensions of RHS of all the options and match with that of the length. As all the options contain some common terms that are and , so we to find out the dimensions of these quantities.
We know that the potential energy of two equal charges separated by a distance from it is given by
So,
For calculating the dimension we can take as as both will have the same dimension. And is a dimensionless quantity.
Dimension of
Dimension of
Therefore, the dimension of
Now, we know that the kinetic energy and dimension of .
As is a dimensionless quantity then the dimension of
Now, is the number per unit volume and the dimension of volume is
Therefore the dimension of .
Now, we will find the dimension of all the options.
For option A, dimension will be
For option B, dimension will be
For option C, dimension will be
For option D, dimension will be
Therefore the dimensions of option B and D are matched with the dimension of length.
Hence, option B and D are correct.
Note: Dimensions of any physical quantity are those raised powers on base units to specify its unit. Dimensional formula is the expression which shows how and which of the fundamental quantities represent the dimensions of a physical quantity.
Complete step by step answer:
As this question has multiple correct options. So, the best way to solve it to eliminate the incorrect options or to check all the options.
We know that the dimension of
We know that the potential energy of two equal charges
So,
For calculating the dimension we can take
Dimension of
Dimension of
Therefore, the dimension of
Now, we know that the kinetic energy
As
Now,
Therefore the dimension of
Now, we will find the dimension of all the options.
For option A, dimension will be
For option B, dimension will be
For option C, dimension will be
For option D, dimension will be
Therefore the dimensions of option B and D are matched with the dimension of length.
Hence, option B and D are correct.
Note: Dimensions of any physical quantity are those raised powers on base units to specify its unit. Dimensional formula is the expression which shows how and which of the fundamental quantities represent the dimensions of a physical quantity.
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