Q.

Young's modulus of elasticity Y is expressed in terms of three derived quantities, namely, the gravitational constant G, Planck's constant h and the speed of light c, as Y=cαhβGγ. Which of the following is the correct option         [2023]

1 α=7, β=-1, γ=-2  
2 α=-7, β=-1, γ=-2  
3 α=7, β=-1, γ=2  
4 α=-7, β=1, γ=-2  

Ans.

(1)

Given, Y=cαhβGγ

ML-1T-2=(LT-1)α(ML2T-1)β(M-1L3T-2)γ

Equating powers

1=β-γ    ...(i)

-1=α+2β+3γ    ...(ii)

-2=-α-β-2γ    ...(iii)

-3=β+γ    ...(iv)

(By adding eq. (ii) & (iii))

Now by adding eq. (i) & (iv) we get,

-2=2β

  β=-1,  γ=-2

-1=α-2-6    α=7