Dimensions - NEET Physics Questions
Question 1: 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 2: 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 3: easy

Dimensions of stress are:

[2020]

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

Stress is Force per unit Area. \([\text{Stress}] = [F]/[A] = (MLT^{-2})/L^2 = ML^{-1}T^{-2}\).

Question 4: easy

The dimensions of \((\mu_0\epsilon_0)^{-1/2}\) are:

[2012 Mains]

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

The speed of light \(c = 1/\sqrt{\mu_0\epsilon_0}\). Therefore, \((\mu_0\epsilon_0)^{-1/2} = c\). The dimensions of speed are \([LT^{-1}]\).

Question 5: easy

The dimension of \(\frac{1}{2}\epsilon_0 E^2\), where \(\epsilon_0\) is permittivity of free space and \(E\) is electric field, is:

[2010 Pre]

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

The expression \(\frac{1}{2}\epsilon_0 E^2\) represents electric energy density, which is Energy per unit Volume. \([\text{Energy density}] = [\text{Energy}]/[\text{Volume}] = (ML^2T^{-2})/L^3 = ML^{-1}T^{-2}\).

Question 6: 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 7: 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 8: easy

The dimensions of universal gravitational constant are:

[2004]

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

From \(F = G \frac{m_1 m_2}{r^2}\), we get \(G = \frac{Fr^2}{m_1 m_2}\). So, \([G] = \frac{(MLT^{-2})(L^2)}{M^2} = M^{-1}L^3T^{-2}\).

Question 9: 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 10: 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 \(F / (A \cdot (\Delta v / \Delta z)) = [MLT^{-2}] / ([L^2] \cdot [T^{-1}]) = [ML^{-1}T^{-1}]\).