Dimensions - NEET Physics Questions
Question 31: 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 32: 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 33: 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 34: 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 35: 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 36: easy

If \(C\) and \(R\) denote capacitance and resistance, the dimensional formula of \(CR\) is:

[1988]

1. \(M^0L^0T^1\)
2. \(M^0L^0T^0\)
3. \(M^0L^0T^{-1}\)
4. Not expressible in terms of MLT
View Answer

The product \(CR\) is the time constant of an RC circuit. Its dimension is time, \(T\), which can be written as \(M^0L^0T^1\).

Question 37: easy

The dimensional formula of angular momentum is:

[1988]

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

Angular momentum is defined as \(L = r \times p\), where \(r\) is distance and \(p\) is linear momentum. Its dimensions are \([L][MLT^{-1}] = [ML^2T^{-1}]\).

Question 38: moderate

If force \([F]\), acceleration \([A]\) and time \([T]\) are chosen as the fundamental physical quantities. Find the dimensions of energy.

[2021]

1. \([F] [A] [T^2]\)
2. \([F] [A] [T^{-1}]\)
3. \([F] [A^{-1}] [T]\)
4. \([F] [A] [T]\)
View Answer

We know \(E = ML^2T^{-2}\), \(F = MLT^{-2}\), \(A = LT^{-2}\), \(T = T\). From \(F = MA\), \(M = F/A\). Substitute \(M\) into \(E\): \(E = (F/A)L^2T^{-2}\). Also, \(L = AT^2\). So, \(E = (F/A)(AT^2)^2T^{-2} = (F/A) A^2 T^4 T^{-2} = F A T^2\).

Question 39: difficult

A physical quantity of the dimensions of length can be formed out of \(c\), \(G\) and \(e^2 / (4\pi\epsilon_0)\), where \(c\) is velocity of light, \(G\) is universal constant of gravitation and \(e\) is charge.

[2017, Delhi]

1. \(c^2 G (e^2 / (4\pi\epsilon_0))^{1/2}\)
2. \(\frac{1}{c^2} G (e^2 / (4\pi\epsilon_0))^{1/2}\)
3. \(\frac{1}{c^2} G \frac{e^2}{4\pi\epsilon_0}\)
4. \(\frac{1}{c^2} \left( G \frac{e^2}{4\pi\epsilon_0} \right)^{1/2}\)
View Answer

Dimensions: \(c = [LT^{-1}]\), \(G = [M^{-1}L^3T^{-2}]\), and \(e^2/(4\pi\epsilon_0) = [ML^3T^{-2}]\). Let's check option d: \(\frac{1}{c^2} \left( G \frac{e^2}{4\pi\epsilon_0} \right)^{1/2} = [L^{-2}T^2] \cdot ([M^{-1}L^3T^{-2}] \cdot [ML^3T^{-2}])^{1/2} = [L^{-2}T^2] \cdot ([L^6T^{-4}])^{1/2} = [L^{-2}T^2] \cdot [L^3T^{-2}] = [L]\).

Question 40: easy

The dimension of Planck constant equals to that of:

[2001]

1. Energy
2. Momentum
3. Angular momentum
4. Power
View Answer

Planck's constant \(h\) has dimensions \(ML^2T^{-1}\). Angular momentum also has dimensions \(ML^2T^{-1}\).