Question Details

If P represents radiation pressure, C represents speed of light and Q represents radiation energy striking a unit area per second, then non-zero integers x, y and z such that PˣQʸ 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 :

The correct option is x = 1, y = -1, z = 1.

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

1. Radiation Pressure (P):
Pressure is defined as force per unit area.
[Force]=[MLT-2]
[Area]=[L2]
Therefore, the dimensional formula for pressure P is:
[P]=[MLT-2][L2]=[ML-1T-2]

2. Radiation Energy striking a unit area per second (Q):
This quantity represents energy per unit area per unit time.
[Energy]=[ML2T-2]
[Area]=[L2]
[Time]=[T]
Therefore, the dimensional formula for Q is:
[Q]=[ML2T-2][L2][T]=[MT-3]

3. Speed of Light (C):
Speed is distance traveled per unit time.
[C]=[LT-1]

Now, we set up the requirement for the expression PxQyCz to be dimensionless:
[PxQyCz]=[M0L0T0]

Substitute the dimensional formulas into the expression:
[ML-1T-2]x[MT-3]y[LT-1]z=[M0L0T0]

Combining the exponents for each fundamental dimension:
[Mx+yL-x+zT-2x-3y-z]=[M0L0T0]

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

Substituting y=-x and z=x into the third equation:
-2x-3(-x)-x=-2x+3x-x=0
This equation is satisfied for any values of x, y, and z as long as y=-x and z=x.

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

This matches the correct option: x = 1, y = -1, z = 1.

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