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Question: Answered & Verified by Expert

If E and E0 denote energies at time t and t0 respectively, and L and L0 distance from some point at t and t0 respectively, then which of the following equations can be declared to be incorrect on dimensional grounds

(A) E=2E0LL0

(B) E=E0e-2LL0

(C) E=2Le-LE0

(D) E=2E0L0×e-LL0

PhysicsUnits and DimensionsTS EAMCETTS EAMCET 2022 (18 Jul Shift 1)
Options:
  • A A,B only
  • B A,C only
  • C A,C,D only
  • D C,D only
Solution:
2859 Upvotes Verified Answer
The correct answer is: C,D only

Dimensions of energy =E=E0=ML2T-2

Dimensions of length

=L=L0=M0L1T0

For A:

LHS =ML2T-2

RHS =ML2T-2LL=ML2T-2

In this case, LHS=RHS

For B:

Exponent should be dimensionless. As we can see

-2LL0=LL=M0L0T0

and LHS =ML2T-2

and RHS =ML2T-2

So in this case, LHS=RHS

For C:

Exponent should be dimensionless but here

-L0E0=M0L1T0ML2T-2=M-1L-1T2

is not dimensionless therefore it is wrong.

For D:

Exponent should be dimensionless. Here

-LL0=M0L0T0M0L0T0=M0L0T0

Now, LHS =E=ML2T-2

and RHS =ML2T-2L=ML1T-2

As in this case, LHS RHS, hence it is wrong.

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