Question Details

P represents radiation pressure, c represents speed of light and S represents radiation energy striking per unit area per sec. The non-zero integers x, y, z such that Pˣ Sʸ cᶻ is dimensionless, are

Options

A

x=1,y=1,z=1

B

x=-1,y=1,z=1

C

x=1,y=-1,z=1

D

x=1,y=1,z=-1

Correct Answer :

x=1,y=-1,z=1

Solution :

To find the non-zero integers x, y, and z such that the expression PxSycz is dimensionless, we first determine the dimensional formulas for each of the physical quantities involved.

1. Radiation Pressure (P):
Pressure is defined as force per unit area.
[P]=[Force][Area]=[MLT-2][L2]=[ML-1T-2]

2. Radiation Energy striking per unit area per second (S):
This quantity represents energy per unit area per unit time.
[S]=[Energy][Area]×[Time]=[ML2T-2][L2]×[T]=[MT-3]

3. Speed of Light (c):
Since c is a speed, its dimensional formula is:
[c]=[LT-1]

Now, we require the product PxSycz to be dimensionless, which means:
[PxSycz]=[M0L0T0]

Substitute the dimensions of P, S, and c into the equation:
[ML-1T-2]x[MT-3]y[LT-1]z=[M0L0T0]

Combining the exponents for M, L, and T on the left-hand side:
[Mx+yL-x+zT-2x-3y-z]=[M0L0T0]

By equating the powers on both sides, we obtain a system of three linear equations:
1) For M: x+y=0y=-x
2) For L: -x+z=0z=x
3) For T: -2x-3y-z=0

Let us check the third equation by substituting y=-x and z=x:
-2x-3(-x)-x=-2x+3x-x=0
This confirms that the relations y=-x and z=x are consistent.

Setting x=1, we find:
y=-1
z=1

Thus, the non-zero integers that make the expression dimensionless are x=1, y=-1, and z=1.

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