#### 12th Standard Physics English Medium Reduced Syllabus Model Question paper with answer key - 2021 Part - 2

12th Standard

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Physics

Time : 02:45:00 Hrs
Total Marks : 70

Part I

Choose the most suitable answer from the given four alternatives and write the option code with the corresponding answer.

15 x 1 = 15
1. Two identical point charges of magnitude –q are fixed as shown in the figure below. A third charge +q is placed midway between the two charges at the point P. Suppose this charge +q is displaced a small distance from the point P in the directions indicated by the arrows, in which direction(s) will +q be stable with respect to the displacement?

(a)

A1 and A2

(b)

B1 and B2

(c)

both directions

(d)

No stable

2. The total electric flux for the following closed surface which is kept inside water

(a)

$\frac { 80q }{ { \varepsilon }_{ 0 } }$

(b)

$\frac { q }{ { 40\varepsilon }_{ 0 } }$

(c)

$\frac { q }{ { 80\varepsilon }_{ 0 } }$

(d)

$\frac { q }{ { 160\varepsilon }_{ 0 } }$

3. An electric field $\vec { E } =10x\hat { i }$ exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

(a)

10 V

(b)

-20 V

(c)

+20 V

(d)

-10 V

4. The figure shows tow parallel equipotential surface A and B kept at a small distance 'r' a part from each other. A point change of Q coulomb is taken from the surface A to B. The amount of net work done will be

(a)

$W=\frac { -1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r }$

(b)

$W=\frac { 1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r }$

(c)

$W=\frac { -1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r^2 }$

(d)

zero

5. During charging a capacitor variation of potential V of the capacitor with time t as shown a

(a)

(b)

(c)

(d)

6. A toaster operating at 240 V has a resistance of 120 Ω. The power is ___________

(a)

400 W

(b)

2 W

(c)

480 W

(d)

240 W

7. An electron moves in a straight line inside a charged parallel plate capacitor of uniform charge density σ. The time taken by the electron to cross the parallel plate capacitor undeflected when the plates of the capacitor are kept under constant magnetic field of induction  $\vec{B}$ is ____________

(a)

${ \varepsilon }_{ ° }\frac { eIB }{ \sigma }$

(b)

${ \varepsilon }_{ ° }\frac { IB }{ \sigma {I} }$

(c)

${ \varepsilon }_{ ° }\frac { IB }{ {e}\sigma }$

(d)

${ \varepsilon }_{ ° }\frac { IB }{ \sigma }$

8. A bar magnet of length l and magnetic moment Pm is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be ____________

(a)

Pm

(b)

$\frac{3}{\pi} p_{m}$

(c)

$\frac{2}{\pi} p_{m}$

(d)

$\frac{1}{2} p_{m}$

9. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.

The potential difference developed across the ring when its speed v, is _____________

(a)

Zero

(b)

$\frac { { Bv\pi { r }^{ 2 } } }{ 2 }$ and P is at higher potential

(c)

πrBv and R is at higher potential

(d)

2rBv and R is at higher potential

10. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is ____________

(a)

2.5 cm

(b)

5cm

(c)

10 cm

(d)

15cm

11. An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is _________

(a)

8 cm

(b)

10 cm

(c)

12 cm

(d)

16 cm

12. An object is initially at a distance of 100 cm from the plane mirror. If the mirror approaches the object at a speed of 5 cms, then after 6 s the distance between the object and its images will be _____________.

(a)

60 cm

(b)

140 cm

(c)

170cm

(d)

150cm

13. An object 2.5 cm high is placed at a distance of 10 cm from a concave mirror of radius of curvature 30 cm. The size of the image is _______________.

(a)

9.2 cm

(b)

10.5 cm

(c)

5.6 cm

(d)

7.5 cm

14. If the nuclear radius of 27Al is 3.6 fermi, the approximate nuclear radius of 64Cu, in femi is __________

(a)

2:4

(b)

1.2

(c)

4.8

(d)

3.6

15. One of the of Young’s double slits is covered with a glass plate as shown in figure. The position of central maximum will __________

(a)

get shifted downwards

(b)

get shifted upwards

(c)

will remain the same

(d)

data insufficient to conclude

16. Part II

Answer any 6 questions. Question no. 16 is compulsory.

6 x 2 = 12
17. Write the uses of Radio waves.

18. Why are Infrared radiation referred to as heatwaves? Name the radiations, which are next to these radiation having
(i) shorter λ
(ii) longer λ.

19. For the same angle of incidence, the angles of refraction in media P, Q and R are 35°, 25°, 15° respectively. In which medium will the velocity of light be minimum?

20. What is the role of nanostructure in the morpho butterfly wings?

21. Write the difference of real and virtual images by a plane mirror.

22. Define internal field emission or field ionization.

23. Part III

Answer any 6 questions. Question no.27 is compulsory.

6 x 3 = 18
24. Two small-sized identical equally charged spheres, each having mass 1 g are hanging in equilibrium as shown in the figure. The length of each string is 10 cm and the angle θ is 30° with the vertical. Calculate the magnitude of the charge in each sphere. (Take g = 10 ms−2)

25. A block of mass m and positive charge q is placed on an insulated frictionless inclined plane as shown in the figure. A uniform electric field E is applied parallel to the inclined surface such that the block is at rest. Calculate the magnitude of the electric field E.

26. Obtain the expression for energy stored in the parallel plate capacitor.

27. Describe the microscopic model of current and obtain general form of Ohm’s law.

28. Discuss the working of cyclotron in detail.

29. A cylindrical bar magnet is kept along the axis of a circular solenoid. If the magnet is rotated about its axis, find out whether an electric current is induced in the coil.

30. Part IV

5 x 5 = 25
31. The current through an element is shown in the figure. Determine the total charge that pass through the element at a) t = 0 s, b) t = 2 s, c) t = 5s

32. Two singly ionized isotopes of uranium $_{ 92 }^{ 235 }{ Uand_{ 92 }^{ 238 }{ U } }$ (isotopes have same atomic number but different mass number) are sent with velocity 1.00 x 105 m s–1 into a magnetic field of strength 0.500 T normally. Compute the distance between the two isotopes after they complete a semi-circle. Also, compute the time taken by each isotope to complete one semi-circular path. (Given: masses of the isotopes: m235 = 3.90 x 10–25 kg and m238 = 3.95 x 10–25 kg)

33. Let I1 and I2 be the steady currents passing through a long horizontal wire XY and PQ respectively. The wire PQ is fixed in horizontal plane and the wire XY be is allowed to move freely in a vertical plane. Let the wire XY is in equilibrium at a height d over the parallel wire PQ as shown in figure.

Show that if the wire XY is slightly displaced and released, it executes Simple Harmonic Motion (SHM). Also, compute the time period of oscillations.

34. An object is placed at a certain distance from a convex lens of focal length 20 cm. Find the object distance if the image obtained is magnified 4 times.

35. When a light of frequency 9 x 1014 Hz is incident on a metal surface, photoelectrons are emitted with a maximum speed of 8 x 105 ms-1. Determine the threshold frequency of the surface.