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I. Answer all the questions 10 x 1 = 10
1. SI unit of Electric Flux is Nm2C
-1
or Vm
2.
3. Used in calling bell , in cranes.
4. Law of conservation of energy
5. Capacitive reactance is inversely proportional to frequency
6. Gamma rays , X-rays, infrared waves, Radio waves.
7. Scattering of light
8. Using light of lower wavelength or placing a medium with higher refractive index
between object and lens
9.
+ + Q
10.
II. Answer any 5 questions 5 x 2 = 10
11. The force of attraction or repulsion between two static point charges is directly
proportional to the product of magnitudes of charges and inversely proportional to square of the
distance between them.
1 2
2
0
1 q q F . r
4 r
r
$
(where
r
$
is unit vector in the direction of force)
7
12. (a) Capacitance becomes C/2 (b) 5C
13. (a) Not applicable for semiconductor devices
(b)Not applicable for fluctuating p.d.’s
(c) Not applicable for varying physical conditions such as temperature .
(d) Not applicable for devices with non-linear Voltage V/s Current graphs
14. V=E/B=5x104 m/s
15.Retentivity – the residual magnetism in the ferromagnetic substance in the absence of
applied external magnetic field .
Coercivity - the reverse magnetic field applied to the ferromagnetic substance to destroy
the residuel magnetism.
16. (a) Due to Flux leakage
(b) Hysterisis loss
(c) Loss due to eddy current
17.Current due to rate of change of electric flux with respect to time.
d o
d
i
dt
18. Electron has longest de-Broglie wavelength
because the wavelength is inversely proportional to square root of mass.
III. Answer any 5 questions 5 x 3 = 15
19.
Consider two points A and B separated by a small distance dx in an electric field E,
produced by a point charge q placed at O. Consider two Equi potential surfaces at A and B
as shown in the fig. Then work done in moving a unit positive charge from A to B against
the electric field is dw = -E dx. (The force applied is E opposite to field E ; = 180)
dV = - E dx
(work is equal to the potential difference between A and B, i.e. dV)
dV E
dx
d
d
x
d
x
+q
O B dx
dd
dx
dx
dx
A
+ 1 C E
e
8
20. Consider a capacitor of capacity C connected to a battery. During the process of charging
at a certain instant let q be the charge and V’ be the p.d between the plates of the
capacitor.
Then
'
q
C
V
or
'
q
V
C
………(1)
The work done by the battery in transferring an additional small quantity of charge dq is
dW = V’dq =
q
dq
C
From (1)
Total work done in charging the capacitor from zero to Q is
0 0 0
1
Q Q Q
q W dw dq q dq
C C
2 1 2 1
2 1 2
Q n
q x x n W x dx x dx
C n
Q
2
1
0
2
Q W
C
2
2
Q W
C
This work done by the battery in charging the capacitor is stored as electric potential
energy U in it. U =
2
2
Q
C
21. Principle of Cyclotron is that the frequency of revolution of a charged particle in a magnetic
field is independent of energy, speed, radius of orbit of the charged particle.