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A physical quantity of the dimensions of length that can be formed out of c, G and (e²)/(4πε₀) is, where c is the velocity of light, G is the universal constant of gravitation and e is charge:

Asked in NEET 2017 · Deriving a relation by dimensional analysis

Answer: (4) 1/(c²)[G(e²)/(4πε₀)]^1/2

Step-by-step solution

Idea: build the dimensional formula of each ingredient first.

[(e²)/(4πε₀)] is an energy times a length: [ML³T⁻²]

[G]=[M⁻¹L³T⁻²]

[G(e²)/(4πε₀)]=[M⁻¹L³T⁻²][ML³T⁻²]=[L⁶T⁻⁴]

Taking the square root: [L³T⁻²]

[c²]=[L²T⁻²], so dividing removes the time:

([L³T⁻²])/([L²T⁻²])=[L]

Why the other options are wrong

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