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Question 32
A
3.47 x 1018 
B
6.93 x 10 20 
C
3.47 x 1020 
D
6.93 x 1018 
Explanation.
Share Answer The number of disintegration,N in time interval At, is given by
- N = Nt
Where N is the number of atoms present at the time t
But ^ = (0.693)/T
N = (0.693)/1(1)/2 Nt = (0.693 x 10)20 x 10/20 = 3.47 x 1018

Correct Option:
A

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Question 33
A
- rays are produced 
B
holes are produced 
C
x - rays are produced 
D
electrons leave a hot element 
Explanation.
Share Answer Thermionic emission is ejection of electron from a metal surface as a result of heating.

Correct Option:
D

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Question 34
A
germanium 
B
silicon 
C
grapefruit 
D
copper 
Explanation.
Share Answer Metals are good conductors due to the presence of free electrons

Correct Option:
D

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Question 35
A
a p-type semiconductor 
B
an n-type semiconductor 
C
an insulator 
D
an intrinsic semi-conductor 
Explanation.
Share Answer When a pentavalent (5 outer electron)atom is added to a pure semiconductor, there is an extra electrons which does not take part in the covalent bonding resulting in an n-type semiconductor.

Correct Option:
B

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Question 36
A
2, -3, -2 
B
-1, 3, -2 
C
-1, 2, -3 
D
-2, -1, 3 
Explanation.
Share Answer
F M1M2
__r2


=> F = GM1M2
__r2

where F is the force of attraction
M1 and M2 are masses of the two bodies, r is the distance between them, and G is the universal gravitational constant
G = _Fr2
M1M2

dimension for force, F = ML = MLT-2
T.T

The dimension for G = MLT-2L2 = L3T-2
_MM_M

= M-1L3T-2
In comparison with MxLyTz, the values for x, y and z = -1, 3, -2

Correct Option:
B

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Question 37
A
117 kmh-1, N31o
B
127 kmh-1, N31o
C
117 kmh-1, N31o
D
127 kmh-1, N31o
Explanation.
Share Answer R2 = 1002 + 602
10000 + 3600 = 13600
R = 13600 = 117km
60kml & = tan = 60/100
tan-1 0.6
= 31o west of the North
117km N31owPhy-explained-image

Correct Option:
C

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Question 38
A
100 m 
B
50m 
C
32 m 
D
18 m 
Explanation.
Share Answer From S = ut + 1/2 at2
S = 1/2 ut2, since U = 0
Let S5 = distance in 5 seconds
= 1/2 x 4 x 52 = 2 x 25 = 50m
S4 = distance covered in 4 seconds
= 1/2 x 4 x 42 = 2 x 16 = 32m
Distance covered in the fifth second
S5 - S4 = 50m - 32m = 18m

Correct Option:
D

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Question 39
A
1.5 ms-1 
B
1.4 ms-1 
C
2.1 ms-1 
D
1.7 ms-1 
Explanation.
Share Answer Sum of momentum before collision
M1 U1 + M2M2
12 x 4.2 + 18 x 0
12 x 4.2
= 50.4
Sum of momentum after collision
(m1 + m2)v
= (12 + 18)v
= 30v
V = 50.4/30
= 1.7ms-1

Correct Option:
D

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Question 40
A
upthrust is equal to the weight of the ball 
B
ball accelerate uniformly 
C
upthrustis equal to the velocity of the ball 
D
velocity is uniform 
Explanation.
Share Answer At vt = terminal velocity
= zero acceleration
= uniform velocityPhy-explained-image

Correct Option:
D

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