JEE MAIN - Physics (2025 - 4th April Morning Shift - No. 2)
설명
To solve this problem, we need to find the dimensions of the electric flux and the magnetic flux, and then take their ratio.
Determine the dimension of electric flux (Φₑ):
Electric flux is defined as
$$\Phi_E = \int_S \mathbf{E} \cdot d\mathbf{A}.$$
The electric field $\mathbf{E}$ has dimensions:
$$[E] = \frac{\text{Force}}{\text{Charge}}.$$
Since force has dimensions $$M L T^{-2},$$ and charge (in SI) has dimensions $$A\,T,$$ we get:
$$[E] = \frac{M L T^{-2}}{A\,T} = M L T^{-3} A^{-1}.$$
The area element $$dA$$ has dimensions $$L^2.$$
Thus, the electric flux has dimensions:
$$[\Phi_E] = [E][A] = M L T^{-3} A^{-1} \times L^2 = M L^3 T^{-3} A^{-1}.$$
Determine the dimension of magnetic flux (Φ_B):
Magnetic flux is defined as
$$\Phi_B = \int_S \mathbf{B} \cdot d\mathbf{A}.$$
The magnetic field $\mathbf{B}$ has dimensions determined via the Lorentz force law (using $$F = q\,v\,B$$), giving:
$$[B] = \frac{F}{q\,v} = \frac{M L T^{-2}}{(A\,T)(L T^{-1})} = M T^{-2} A^{-1}.$$
Again, the area element has dimensions $$L^2.$$
So the magnetic flux has dimensions:
$$[\Phi_B] = [B][A] = (M T^{-2} A^{-1})(L^2) = M L^2 T^{-2} A^{-1}.$$
Find the ratio of electric flux to magnetic flux:
Taking the ratio:
$$\frac{\Phi_E}{\Phi_B} = \frac{M L^3 T^{-3} A^{-1}}{M L^2 T^{-2} A^{-1}}.$$
Canceling like terms:
Mass $(M)$ cancels.
Current $(A^{-1})$ cancels.
For length, $$L^{3-2} = L^1.$$
For time, $$T^{-3 -(-2)} = T^{-1}.$$
Therefore, the ratio has dimensions:
$$L^{1}T^{-1}.$$
This means in the expression
$$M^P L^Q T^R A^S,$$
the exponents for length and time are $$Q = 1$$ and $$R = -1.$$
Looking at the options provided, this corresponds to Option D: $$(1,-1).$$
Thus, the answer is Option D.
