Set-5
1 q
33. Formula: V
4 0 r
Point inbetween
(5x108C) A B (3x108C)
C O
x 16x
Let O be a point at a distance ‘x’ from A (between the charges) where the
potential is zero.
9 5x10 8
At O, potential due to 5x10 C, VA 9 x10
8
x
3x10 8
At O, potential due to 3x108C, VB 9 x10 9
16 x
Net potential at O is zero if
VA VB 0
8
9 5x10 9 3x10 8
9 x10
x 9 x10 16 x 0
5x10 8 3x10 8
9 x10 9 9 x10 9
16 x
x
5 3
805x=3x 80=8x
x 16 x
x=10cm from A in between the charges.
Point outside:
(5x108C) (3x108C)
A B
C O
16+x
x
Let O be a point at a distance ‘x’ from B (outside the charges) where the
potential is zero.
1 q
We have V
4 0 r
5x10 8
At O, potential due to 5x108C, VA 9 x10 9
16 x
9 3x10 8
8
At O, potential due to 3x10 C, VB 9 x10
x
Net potential at O is zero if VA VB 0
5x10 8 3x10 8
9 x10 9 9 x10 9
0
16 x x
5x10 8 3x10 8
9 x10 9 9 x10 9
x
16 x
5 3
5x=48+3x 2x=48
16 x x
X=24cm from B and 40cm from A outside the charges.
34. Formula: V=IR, Node rule and Loop Rules.
The circuit diagram, various nodes and currents through various branches are
shown. Applying KVL to the loop ABDA (traversing clockwise)
E+IR=0
2I2 + 10Ig –8I1 =0
–8I1 +2I2 + 10Ig =0..........(1)
Applying KVL to the loop BCDB
(traversing clockwise) B
I4=I2Ig
4(I2Ig) 4(I1+Ig)10Ig=0
2
4I24Ig 4I14Ig10Ig=0 Ig 4
4I1+4I218Ig = 0............(2) I2
A 10 C
Applying KVL to the loop I1
ABCEA
8 4
(traversing clockwise) I
5+ 2I2+4(I2Ig) = 0 I3=I1+Ig
5+ 2I2+4(I2Ig) = 0 I=I1+I2 D
I
0 + 6I2 4Ig = 5.............(3) E
Multiplying equation (1) by 2
–16I1 +4I2 + 20Ig =0
writing equation (2) again 5V
4I1 + 4I2 18Ig = 0
Subtracting,
–12I1 +0 + 38Ig =0...........(4)
Multiplying equation (1) by 3
–24I1 +6I2 + 30Ig =0 writing equation (3) again
0 + 6I2 4Ig = 5
Subtracting, –24I1 +0 + 34Ig =5...............(5)
Equation (4) x2 –24I1 +0 + 76Ig = 0
Solving, 42Ig = 5
5
Ig 0.119A
42
35. Given power factor Cos = 1 or =0O.
1 1
Hence XL=XC or o or o
LC 2 LC
(i) At resonance frequency, power factor is unity. Hence resonance frequency is
1
o 15.9Hz
2x3.142 200 x10 3 x500 x10 6
V V 100
(ii) Current, I rms rms rms 10A
Z R 10
Current amplitude Io I rms 2 10 2 14.14A
o L 2 o L 2 x 3.142 x15.9 x 200 x10 3
(iii) Q factor = Q= 2
R R 10
o L 1 L
Also note that Q
R R C
D
36. Formula: fringe width,
d
width 20 fringes 8x10 3
0.4mm
20 20
xD 3 546 x10 9 x1.25
0.4x10
d d
9
546 x10 x1.25
d 1.706mm
0.4x10 3
Distance between slits is d=1.706mm.
Fringe width if 594nm is used,
xD 594 x10 9 x1.25
0.435mm
d 1.706 x10 3
Width of 20 fringes = 20=20x0.435=8.7mm
56
37. 26Fe contains 26 protons and 30 neutrons. Formula for Mass defect is
Δm Zm P A Z m n M
m=[26x1.00728 + 30x1.00867] – 55.9349
m=[26.18928 + 30.260] – 55.9349
m=[56.4493 - 55.9349]
m=0.51448u
Hence binding energy of 26Fe56 is
B.E.= m x931MeV=0.51448x931x106ev=478.98MeV
B.E. 478 .98
Specific binding energy, E 8.553MeV
A 56
133
55Cs contains 55 protons and 78 neutrons. Formula for Mass defect is
Δm Zm P A Z m n M
m=[55x1.00728 + 78x1.00867] –132.9049
m=[55.4004 + 78.6726] – 132.9049
m=[134.07666 – 132.9049]
m=1.1718u
Hence binding energy of 55Cs133 is
B.E.= m x931MeV=1.1718x931x106ev=1090.95MeV
B.E. 1090 .95
Specific binding energy, E 8.203MeV
A 56
Specific binding energy of 26Fe56 is greater than specific binding energy of 55Cs133.
Hence 26Fe56 is more stable.