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MARKING SCHEME
Value point/ expected points
Q.No.
1
Marks
Total
Yes.
At a point midway between two equal and opposite charges, the electrical
potential is zero but the electric field is not zero.
R = 60 × 104Ω ,
I= 5× 10-5A
½
½
3
tan δ = Bv/BH = 1
∴ δ =450
½
½
1
4
5
Zero
Slope of the graph is h / √2me
Slope of A is smaller, so A represents heavier particle.
1
½
½
1
R ∝ A 1/3
½
1
1:2
½
2
6
7
(a) Transducer
8
(i) Short wave broadcast services
(ii) Television broadcast (or microwave
links or Satellite communication)
The force experienced per unit charge in the electric field is called electric field
intensity. OR E  Lt F
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(b) Repeater OR Transponder
qo  0
NC-1
qo
Its SI unit is
E is directed towards negative charge of the dipole.
1
½
½
1
1
½+½
1
½+½
1
1
½
2
½
10
2
11
2
12
13
Thus the given values are in good agreement with the theoretically expected
values.
(i) When the separation between the two coils is increased, the flux linked
with the secondary due to the current in the primary, decreases. Hence the
mutual inductance decreases.
(ii) Mutual inductance increases when the number of turns in each coil is
increased, because M ∝ N1N2
(i) The glow gradually increases till it becomes maximum
Reasons : There is a back (induced) emf in the inductor, when the current is
growing and this delays the growth of current to its final steady value.
(ii) The glow will decrease
Reasons : The impedance of circuit will increase due to the presence of the
inductive reactance of the circuit.
OR
1
1
2
½
½
½
½
2
2
14
1½
½
15
The activity of a radioactive element at any instant equals its rate of decay at
that instant.
Its SI unit is Becquerel (Bq) (= 1 decay per second)
½
½
1
2
2
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OR GATE
1
TRUTH TABLE
1
2
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LOS-LINE OF SIGHT
1
½
½
½
½
3
18
Gauss' theorem states that the total electric flux through any closed surface is
proportional to the total electric charge inside the surface. Mathematically
1
½
½
½
½
3
19
Resistivity ,
i)Metals : As the temperature increases, the thermal speed of
electrons increases. Free electrons collide more frequently with the
positive metal ions. The relaxation time decreases. Consequently,
the resistivity of the metal increases.
(ii) Semiconductors : The relaxation time does not change with the
temperature. But the number density (n) of free electrons increases
exponentially with temperature. As result, the sensitivity of
semiconductor decreases exponentially with the increase in
temperature.
20
Kirchhoff’s rules for electrical networks are as follows:(i) Junction rule: At any junction, the sum of the currents entering
the junction is equal to the sum of currents leaving the junction.
(ii) Loop rule: The algebraic sum of the changes in potential around
any closed loop involving resistors and cells in the loop is zero.
Applying Kirchhoff’s rules for the loop ABCD and for the loop DCFE, we get,
40I3 + 20I1 = -40
12 + 2I3 =6
Applying Junction rule at D, 13 = I1 + I2
Solving the above three equations, we get, I1 = -3.6A
1
1
1
3
½
½
½
½
½
½
3
21
(a) Step down transformer.
½
1
Principle-A transformer is based on the principle of mutual induction.
Working-When an alternating voltage is applied to the primary, the resulting
current produces an alternating magnetic flux which links the secondary
and induces an emf in it. The value of this emf depends on the number of
turns in the secondary.
½
1
Let Φ be the flux in each turn in the core at time t due to current in the
primary when a voltage vp is applied to it. Then the induced emf or voltage εs,
in the secondary with Ns turns is
The alternating flux Φ also induces an emf, called back emf in the
primary. This is
3
22
i) U-V rays, ii) Microwaves, iii) Infrared Radiation & iv) X-rays
ii) λ 2, λ 3, λ 4, λ 1
4*½=2
1
23
½
½
½
½
3
1
3
24
½
Work function
½
(i) Photoelectric current increases, due to increase of intensity
½+½
(ii) No change, as stopping Potential is independent of intensity.
½+½
3
OR
Threshold frequency: The minimum frequency of the incident radiation for a
given metal below which emission of photo electrons does not take place.
Stopping potential: The minimum negative potential of the anode (collector)
for which photo electric current becomes zero.
1
(c) (i) (Practically) No effect/remain same. –
½
1
As increase in frequency does not significantly change the number of photons
in the beam.
(ii) Increases
the number of incident photons increases
½
3
25
2
1
3
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Curiosity to learn, approaching the teacher to learn new things, inquisitiveness
2
1
1
27
1
1
1
4
1
1
5
1
1
OR
½
½
1
½
½
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5
1
1/2
1
5
1
b.
OR
1
Considering the refraction of a point object on the surface XP1Y, the image is
formed at I1 who is at a distance of V1.
CI1= P1I1 = V1 (as the lens is thin)
CC1 = P1C1 = R1
CO = P1O = u
It follows from the refraction due to convex spherical surface XP1Y
½
The refracted ray from A suffers a second refraction on the surface XP2Y and
emerges along BI. Therefore I is the final real image of O.
Here the object distance is
(Note P1P2 is very small)
(Final image distance)
Let R2 be radius of curvature of second surface of the lens.
\ It follows from refraction due to concave spherical surface from denser to
rarer medium that
½
Adding (1) & (2)
½
½
½
½
(ii) The rays must fall normally on the
plane mirror so that the image of
the pin coincides with itself
½
½
5
Hence rays, like CA and DB, form a
parallel beam incident on the lens.
P is the position of the focus of the lens
Distance OP equals the focal length of
the lens.
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Circuit diagram used to study the characteristics of an npn transistor in
common emitter configuration.
2
1
1
½
½
5
OR
An oscillator is a device which can produce undamped electromagnetic
oscillations of desired frequency and amplitude. It converts d.c in to a.c.
½
when feedback is positive
½
½
Circuit diagram
1½
Working- 1.LC oscillator produces damped oscillations due to inherent
electrical resistance.
2.To have undamped oscillations transistors can be used to give +ve feed back
from the output circuit to the input circuit.
3.K is closed; magnetic flux is linked with L’as well as L increases (inductively
coupled). Induced ‘emf’ is set up in such a way that the emitter base is forward
biased, IE increases and hence IC also increases.
4.Magnetic flux across L’ & L increases, IC increases and reaches the saturation
value.
2
5.Induced ‘emf’ in ‘L’ becomes zero.
6.Magnetic flux charges L & ‘L’ induces ‘emf’ in such a direction it decreases
the forward bias. IE decreases also IC. IC reaches zero. This process is repeated.
7.The cycle again repeats and hence the oscillations are produced.
The output is obtained across T3.
8.The frequency of oscillations is given by
5