16.(JEE Main 2020 (Online) 2nd September Morning Slot
)
If speed V, area A and force F are chosen as
fundamental units, then the dimension of
Young’s modulus will be
(A) FA–1V0
(B) FA2V–1
(C) FA2V–2
(D) FA2V–3
Correct answer is (A)
Y = k [F]x
[A]y
[V]z
[M1L1T
–2] = [MLT–2]x [L2]y
[LT–1]z
[M1L1T
–2] = [M]x [L]x+2y+z[T]–2x–z
Comparing power of M, L and T
x = 1 ……(1)
x + 2y + z = –1 ……(2)
–2x – z = –2 ……(3)
After solving
x = 1
y = –1
z = 0
Y = FA–1V0
17.(JEE Main 2020 (Online) 8th January Morning Slot
)
The dimension of stopping potential V0 in photoelectric effect in units of Planck's constant 'h',
speed of light 'c' and Gravitational constant 'G' and ampere A is :
(A) h1/3 G2/3 c1/3 A–1
(B) h0 c5 G-1 A-1
(C) h2/3 c5/3 G1/3 A–1
(D) h2 G3/2 c1/3 A–1
Correct answer is (B)
V0
hPcQGRIS
[V0] = [M1L2T–3A–1]
[c] = [L1T–1]
[h] = [M1L2T–1]
[G] = [M–1L3T–2]
[I] = [A]
[M1L2T–3A–1] = [MP–R L2P+Q+3R
T–P–Q–2R AS]
Comparing dimension of M, L, T, A, we get
P – R = 1 ; 2P + Q + 3R = 2
– P – Q – 2R = – 3 ; S = – 1
P = 0, Q = 5, R = –1, S = –1
V0
h0 c5 G-1
A-1
18.(JEE Main 2019 (Online) 8th April Evening Slot
)
If surface tension (S), Moment of inertia (I) and
Planck's constant (h), were to be taken as the
fundamental units, the dimensional formula for
linear momentum would be :-
(A) S1/2I1/2h0
(B) S3/2I1/2h0
(C) S1/2I1/2h-1
(D) S1/2I3/2h-1
Correct answer is (A)
We know,
surface tension (S) =
=
[S] =
Moment of inertia (I) = mr2
[I] =
Planck's constant (h) =
= Et
[h] =
Also linear momentum (p) = mv =
Now we have to express p in terms of s, I and h.
Let, [P] = [Sa Ib
hc]
=
abc
= [ Ma + b + c L2b +2c T-
2a - c ]
By comparing the dimensions of both sides, we get
a + b + c = 1 .........(1)
2b +2c = 1 ..............(2)
- 2a - c = -1 ...................(3)
By solving those three equations we get,
a =
b =
c = 0
linear momentum [p] =
[S1/2I1/2h0]
19.(JEE Main 2019 (Online) 11th January Evening Slot
)
If speed (V), acceleration (A) and force (F) are considered as fundamental units, the dimension of Young,s
modulus will be:
(A) V2A2F2
(B) V4A2F
(C) V4A2F
(D) V2A2F2
Correct answer is (C)
We know,
Young's modulus (Y) =
[Y] =
= [ ML-1T-2]
Let [Y] = [V]x [A]y [F]z
[ ML-1T-2] =
[LT-1]x [LT-2]y
[MLT-2]z
[ ML-1T-2] =
[ Mz Lx + y + z T-x -2y - 2z
For dimensional balance, the dimension on both sides should be same.
So, z = 1
x + y + z = -1
x + y = -2 ........(1)
and -x -2y - 2z = -2
x + 2y = 0 ...........(2)
By solving those two equations we get,
x = -4 and y = 2
[Y] =
V4A2F1
20.(JEE Main 2019 (Online) 9th January Evening Slot
)
Expression for time in terms of G(universal gravitional constant), h (Planck constant) and c (speed of light)
is proportional to :