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36.(JEE Main 2019 (Online) 8th April Morning Slot )

In SI units, the dimesions of 0 μ 0 is :

(A) A–1 TML3

(B) A2T3M–1L–2

(C) AT–3ML3/2

(D) AT2M–1L–1

Correct answer is (B)

0 μ 0 = 0 μ 0 0 = c × 0

[ 0 μ 0 ] = [ L T 1 ] × [ 0 ]

We know, F = 1 4 π 0 q 2 r 2

0 = q 2 4 π r 2 F

[ 0 ] = [ A T ] 2 [ M L T 2 ] × [ L 2 ] = [ A 2 M 1 L 3 T 4 ]

[ 0 μ 0 ] = [ L T 1 ] × [ A 2 M 1 L 3 T 4 ]

                 = [A2T3M–1L–2]

37.(JEE Main 2019 (Online) 12th January Evening Slot )

Let , r, C and V represent inductance, resistance, capacitance and voltage, respectively. The dimension of r C V in SI units will be :

(A) [A–1]

(B) [LTA]

(C) [LA–2]

(D) [LT2]

Correct answer is (A)

[ r ] = T

[CV] = AT

So,    [ r C V ] = T A T = [A 1]

38.(JEE Main 2016 (Online) 9th April Morning Slot )

In the following ‘I’ refers to current and other symbols have their usual meaning. Choose the option that corresponds to the dimensions of electrical conductivity :

(A) ML 3 T 3 I2

(B) M 1 L3 T3 I

(C) M 1 L 3 T3 I2

(D) M 1 L 3 T3 I

Correct answer is (C)

We know. resistivity ( ρ ) = R A L

and conductivity = 1 ρ = 1 R A

As   R = V I

   conductivity = L I V A

Also  V = ω q = ω i t = [ M L 2 T 2 ] [ I ] [ T ] = [ M L 2 T 3 I 1 ]

   Conductivity = [ L ] [ I ] [ M L 2 T 3 I 1 ] [ L 2 ]

=    [ M 1 L 3 T 3 I 2 ]

39.(JEE Main 2013 (Offline) )

Let [ ε 0 ] denote the dimensional formula of the permittivity of vacuum. If M = mass, L = length, T = time and A = electric current, then:

(A) ε 0 = [ M 1 L 3 T 2 A ]

(B) ε 0 = [ M 1 L 3 T 4 A 2 ]

(C) ε 0 = [ M 1 L 2 T 1 A 2 ]

(D) ε 0 = [ M 1 L 2 T 1 A ]

Correct answer is (B)

From Coulomb's law we know,

F = 1 4 π 0 q 1 q 2 r 2

0 = 1 4 π q 1 q 2 F r 2

Hence, [ 0 ] = [ A T ] [ A T ] [ M L T 2 ] [ L 2 ]

= [ M 1 L 3 T 4 A 2 ]

40.(AIEEE 2008 )

The dimension of magnetic field in M, L, T and C (coulomb) is given as

(A) MLT-1C-1

(B) MT2C-2

(C) MT-1C-1

(D) MT-2C-1

Correct answer is (C)

We know that,
Lorentz force | F | = | q v × B |

[ B ] = [ F ] [ q ] [ v ] = [ M L T 2 ] [ C ] × [ L T 1 ] = [ M T 1 C 1 ]