Dimensions - NEET Physics Questions
Question 1: moderate

If energy \((E)\), velocity \((V)\) and time \((T)\) are chosen as fundamental quantities the dimensional formula for momentum \((P)\) is:

1. \([E^1 V^{-1} T^0]\)
2. \([E^{-1} V^1 T^1]\)
3. \([E^{-1} V^{-1} T^{-1}]\)
4. \([E^0 V^0 T^1]\)
View Answer

Since Energy \(E = F \cdot d = P \cdot V\), momentum \(P = E V^{-1} T^0\). Thus, the dimensional formula is \([E^1 V^{-1} T^0]\).

Question 2: moderate

The dimension \([ML^{-2}T^{-2}A^2]\) belong to the:

[2022]

1. electric permittivity
2. magnetic flux
3. self inductance
4. magnetic permeability
View Answer

The dimension of magnetic permeability is \(MLT^{-2}A^{-2}\). The given dimension \(ML^{-2}T^{-2}A^2\) does not match a standard physical quantity listed. Assuming a typo and it refers to magnetic permeability.

Question 3: moderate

If \(E\) and \(G\) respectively denote energy and gravitational constant, then \(\frac{E}{G}\) has the dimensions of:

[2021]

1. \([M][L]^{-1}[T]^{-1}\)
2. \([M^{2}][L]^{0}[T]^{0}\)
3. \([M^{2}][L]^{-2}[T]^{-1}\)
4. \([M^{2}][L]^{-1}[T]^{0}\)
View Answer

Energy \([E] = ML^2T^{-2}\) and Gravitational Constant \([G] = M^{-1}L^3T^{-2}\). So \([E/G] = M^2L^{-1}T^0\).

Question 4: moderate

Which two of the following five physical parameters have the same dimensions?
A. Energy density
B. Refractive index
C. Dielectric constant
D. Young’s modulus
E. Magnetic field

[2008]

1. (A) and (D)
2. (B) and (D)
3. (C) and (E)
4. (A) and (D)
View Answer

Energy density (A) is \(ML^{-1}T^{-2}\). Young's modulus (D) is Stress/Strain, so also \(ML^{-1}T^{-2}\). Therefore, (A) and (D) have the same dimensions.

Question 5: moderate

Dimensions of resistance in an electrical circuit, in terms of dimension of mass \(M\), of length \(L\), of time \(T\) and of current \(I\), would be:

[2007]

1. \(ML^2T^{-2}\)
2. \(ML^2T^{-3}I^{-1}\)
3. \(ML^2T^{-3}I^{-2}\)
4. \(ML^2T^{-3}I^{-1}\)
View Answer

Resistance \(R = V/I = (W/q)/I = W/(I^2T)\). Work \([W] = ML^2T^{-2}\). So, \([R] = (ML^2T^{-2})/(I^2T) = ML^2T^{-3}I^{-2}\).

Question 6: moderate

Which pair have not equal dimensions?

[2000]

1. Energy and torque
2. Force and impulse
3. Angular momentum and Planck's constant
4. Elastic modulus and pressure
View Answer

Force has dimensions \(MLT^{-2}\) and impulse has dimensions \(MLT^{-1}\). These are not equal.

Question 7: moderate

The dimensions of impulse are equal to that of:

[1996]

1. Pressure
2. Linear momentum
3. Force
4. Angular momentum
View Answer

Impulse is defined as change in momentum. Therefore, their dimensions are equal, \(MLT^{-1}\).

Question 8: moderate

The dimensional formula of permeability of free space \(\mu_0\) is

[1991]

1. \(MLT^{-2}A^{-2}\)
2. \(M^0L^{-1}T\)
3. \(M^0LT^{-1}A^2\)
4. None of these
View Answer

From Ampere's law, the dimensions of permeability of free space \(\mu_0\) are derived as \(MLT^{-2}A^{-2}\).

Question 9: moderate

According to Newton, the viscous force acting between liquid layers of area \(A\) and velocity gradient \( \Delta v / \Delta z \) is given by \(F = -\eta A (\Delta v / \Delta z)\), where \(\eta\) is constant called coefficient of viscosity. The dimensional formula of \(\eta\) is:

[1990]

1. \(ML^{-2}T^{-2}\)
2. \(ML^0T^0\)
3. \(ML^2T^{-1}\)
4. \(ML^{-1}T^{-1}\)
View Answer

From the formula \(F = -\eta A (\Delta v / \Delta z)\), the dimension of \(\eta\) is \(F / (A \cdot (\Delta v / \Delta z)) = [MLT^{-2}] / ([L^2] \cdot [T^{-1}]) = [ML^{-1}T^{-1}]\).

Question 10: moderate

Which of the following quantities, which one has dimensions different from the remaining three?

[1989]

1. Energy per unit volume
2. Force per unit area
3. Product of voltage and charge per unit volume
4. Angular momentum
View Answer

Energy per unit volume, force per unit area, and product of voltage and charge per unit volume all have dimensions \(ML^{-1}T^{-2}\). Angular momentum has dimensions \(ML^2T^{-1}\), which is different.