Question Details

The quantities which have the same dimensions as those of solid angle are:

Options

A

strain and angle

B

stress and angle

C

strain and arc

D

angular speed and stress

Show Answer

Correct Answer :

Option A

strain and angle

strain and angle

Solution :

To find the quantities that have the same dimensions as those of a solid angle, let's analyze the dimensions of each quantity mentioned in the problem.

First, let's consider the solid angle (Ω).
The solid angle is defined as the ratio of the area of a portion of a spherical surface to the square of the radius of the sphere:
Ω=AreaRadius2
The dimension of area is L2, and the dimension of the square of the radius is also L2.
Therefore, the dimensional formula for solid angle is:
[Ω]=[L2][L2]=[M0L0T0]
Thus, the solid angle is a dimensionless quantity.

Now, let's evaluate the dimensions of the quantities in the options:

1. Strain:
Strain is defined as the ratio of change in dimension to the original dimension (for example, change in length divided by original length):
Strain=ΔLL
Since it is the ratio of two identical physical quantities (lengths), it is dimensionless:
[Strain]=[M0L0T0]

2. Angle (Plane Angle):
A plane angle (θ) is defined as the ratio of arc length to the radius of the circle:
θ=ArcRadius
Since both arc length and radius have the dimension of length (L), the plane angle is also dimensionless:
[Angle]=[L][L]=[M0L0T0]

3. Stress:
Stress is defined as force per unit area:
Stress=ForceArea
Its dimensional formula is:
[Stress]=[MLT-2][L2]=[ML-1T-2]
This is not dimensionless.

4. Arc:
An arc is a segment of a curve, which has the dimension of length:
[Arc]=[L]
This is not dimensionless.

5. Angular Speed (ω):
Angular speed is the rate of change of angular displacement:
ω=dθdt
Its dimensional formula is:
[ω]=[T-1]
This is not dimensionless.

Comparing these results, we find that both strain and angle are dimensionless quantities, meaning they have the dimensional formula [M0L0T0], which is identical to that of a solid angle.

Therefore, the correct option is strain and angle.

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