Physics Units, Dimensions and Measurement JEE Main 2025 - ( Units and Dimensions ) MCQ (Single Correct)

In an electromagnetic system, the quantity representing the ratio of electric flux and magnetic flux has dimension of , where value of ' ' and ' ' are

A
B

C
D

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Text Solution

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The correct answer is:
D

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 :

Electric flux is defined as

The electric field has dimensions:

Since force has dimensions , and charge (in SI) has dimensions , we get:

.

The area element has dimensions .
Thus, the electric flux has dimensions:

Determine the dimension of magnetic flux ( ):
Magnetic flux is defined as

The magnetic field has dimensions determined via the Lorentz force law (using ), giving:

Again, the area element has dimensions .
So the magnetic flux has dimensions:

Find the ratio of electric flux to magnetic flux:
Taking the ratio:

Canceling like terms:
Mass ( ) cancels.
Current ( ) cancels.
For length, .
For time, .

Therefore, the ratio has dimensions:

This means in the expression

the exponents for length and time are and .

Looking at the options provided, this corresponds to Option D: ( ).

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