#### 12th Standard English Medium Physics Reduced syllabus Public Exam Model Question Paper with Answer key - 2021

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. 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 J

(b)

-20 J

(c)

+20 J

(d)

-10 J

2. A wire of resistance 2 ohms per meter is bent to form a circle of radius 1m. Th e equivalent resistance between its two diametrically opposite points, A and B as shown in the fi gure is

(a)

$\pi \Omega$

(b)

$\frac{\pi}{2}\Omega$

(c)

2$\pi \Omega$​​​​​​​

(d)

$\frac{\pi}{4}\Omega$

3. A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of

(a)

each of them increases

(b)

each of them decreases

(c)

copper increases and germanium decreases

(d)

copper decreases and germanium increases

4. Th e force experienced by a particle having mass m and charge q accelerated through a potential diff erence V when it is kept under perpendicular magnetic field $\vec { B }$ is

(a)

$\sqrt { \frac { 2{ q }^{ 3 }BV }{ m } }$

(b)

$\sqrt { \frac { { q }^{ 3 }{ B }^{ 2 }V }{ 2m } }$

(c)

$\sqrt { \frac { 2{ q }^{ 3 }{ B }^{ 2 }V }{ m } }$

(d)

$\sqrt { \frac { { 2q }^{ 3 }BV }{ { m }^{ 3 } } }$

5. The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenonid to demagnetize the ferromagnet completely is

(a)

1.00 m A (milli ampere)

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

6. A simple pendulum with charged bob is oscillating with time period T and let θ be the angular displacement. If the uniform magnetic field i switched ON in a direction perpendicular to the plane of oscillation then

(a)

time period will decrease but θ will remain constant

(b)

time period remain constant but θ will decrease

(c)

both T and θ will remain the same

(d)

both T and θ will decrease

7. When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. Th e co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

8. The instantaneous values of alternating current and voltage in a circuit are $i=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t \right)$ A and v=$=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t+\frac { \pi }{ 3 } \right) V.$The average power in watts consumed in the circuit is

(a)

$\frac{1}{4}$

(b)

$\frac{\sqrt3}{4}$

(c)

$\frac{1}{2}$

(d)

$\frac{1}{8}$

9. A radiation of energy E falls normally on a perfectly refl ecting surface. Th e momentum transferred to the surface

(a)

$\frac{E}{c}$

(b)

2$\frac{E}{c}$

(c)

Ec

(d)

$\frac { E }{ { c }^{ 2 } }$

10. If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the emitted electron is (Take h = 6.6 × 10–34 Js)

(a)

<2.75×10−9m

(b)

≥2.75×10−9m

(c)

≤2.75×10−12m

(d)

<2.5×10−10m

11. mirror of focal length of f and the maximum and minimum distance of

(a)

1

(b)

2

(c)

3

(d)

4

12. The particle size of ZnO material is 30 nm. Based on the dimension it is classified as

(a)

Bulk material

(b)

Nanomaterial

(c)

Soft material

(d)

Magnetic material

13. The gravitational waves were theoretically proposed by

(a)

(b)

Marie Curie

(c)

Albert Einstein

(d)

Edward Purcell

14. Light transmitted by Nicol prism is,

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

15. Th e principle in which a solar cell operates

(a)

Diffusion

(b)

Recombination

(c)

Photovoltaic action

(d)

Carrier flow

16. Part II

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

6 x 2 = 12
17. Define Rectification.

18. Define Zener effect

19. Explain knee voltage

20. What is called logical variables?

21. What is Breakdown voltage?

22. What are carrier waves?

23. Part III

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

6 x 3 = 18
24. Derive an expression for electrostatic potential due to a point charge.

25. Obtain the expression for electric field due to an infinitely long charged wire.

26. Calculate the equivalent resistance between A and B in the given circuit.

27. Calculate the magnetic flux coming out from the surface containing magnetic
dipole (say, a bar magnet) as shown in figure.

28. Calculate the magnetic field inside and outside of the long solenoid using Ampere’s circuital law.

29. If the current i flowing in the straight conducting wire as shown in the figure decreases, find out the direction of induced current in the metallic square loop placed near it.

30. Part IV

5 x 5 = 25
31. In Young's double slit experiment monochromatic ligt of wavelength 630 nm illuminates the pair of slits and produces an interference pattern in which two consecutive bring fringes are separated by 8.1 mm. Anther source of monochromatic light produces the interference pattern in which the two consecutive bright fringes are separated by 7.2 mm. Find the wavelength of light from the second source. What is the effect on the interference fringes in the monochromatic source is replaced by a source of white light?

32. If the focal lengths of the objective and eyepiece of a microscope are 2 cm and 5 cm and 5 cm respectively and the distance between them is 20 cm, what is the distance of the object from the objective when the image seen by the eye is 25 cm from eyepiece? Also find the magnifying power.

33. Two polaroids are set in crossed positions. A third polaroid is placed between the two making an angle e with the pass axis of the first polaroid. Write the expression for the intensityof light transmitted from the second polaroid. In what orientations will the transmitted intensity be (i) minimum and (ii) maximum.

34. A telescope has an objective of diameter 60 cm, The focal lengths of the objective and eyepiece are 2.0 m and 1.0 cm respectively. The telescope is directed to view two distant almost point sources of light, (e.g., two stars of a binary). The sources are roughly at the same distance = (=104 light year) along the line of sight hut are separated transverse to the line of sight by a distance of 1010 m. Will the telescope resolve the two objects i.e. will it see two distant stars?

35. For a BJT, the common - base current gain α = 0.98 and the collector base junction reverse bias saturation ICU = 0.6μA. This BJT is connected in the common emitter mode and operated in the active region with a base drive current ID= 20 μA. The collector current IC for this mode of operating is