Q. 163.5( 6 Votes )
If Planck’s const A. Mass of electron (me)
B. Universal gravitational constant (G)
C. Charge of electron (e)
D. Mass of proton (mp )
Answer :
According to plank, the energy of photon is given by the expression,
Where,
f= frequency of light
h= Planck’s constant
Dimension of E=
Dimension of f=
So, dimension of h,
As we can see in the question, we have to relate M, L and T in terms of h and c as fundamental quantities.
There is no charge or ampere dimension so option (c) is eliminated.
We have to check for option a, b and d.
Dimensions of me, mp and G are ,
and
respectively.
For me and mp,
For mass, let
m
By substituting the dimension for each quantity
Now using principal of homogeneity, which states that the dimensions on both sides of a dimensional equation is same, we get
=
Equating like terms and solving above we get,
a+b=1, 2b+c=0, -b-c=0
a=1, b=0, c=0
Substituting the values in equation,
m
m=me
Similarly for length,
l
=
Solving we get,
and for time,
This holds true for both me and mp.
And similarly for G,
Also we know,
Dimension of G=
Let,
m ...........(1)
By substituting the dimension for each quantity
Now using principal of homogeneity, which states that the dimensions on both sides of a dimensional equation is same, we get
=
Equating like terms and solving above we get,
a-c=1, 2a+b+3c=0, -a-b-2c=0
a=1/2, b=1/2, c=-1/2
Substituting the values in equation,
m
Similarly for length and time,
and
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