#### Half Yearly Model Question Paper 2019

12th Standard EM

Reg.No. :
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Physics

Time : 02:30:00 Hrs
Total Marks : 70

Part A

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

15 x 1 = 15
1. Two points A and B are maintained at a potential of 7 V and -4 V respectively. The work done in moving 50 electrons from A to B is

(a)

8.80 × 10-17 J

(b)

-8.80 × 10-17 J

(c)

4.40 × 10-17 J

(d)

5.80 × 10-17 J

2. Three capacitors are connected in triangle as shown in the figure. The equivalent capacitance between the points A and C is

(a)

1μF

(b)

2μF

(c)

3μF

(d)

$\frac{1}{4}$μF

3. A resistance of a metal wire of length AB is 2$\Omega$. Another wire of length PQ of the same metal with twice the diameter of the wire AB is found to have the same resistance of2$\Omega$. What is the length of PQ?

(a)

4 AB

(b)

2 AB

(c)

1AB

(d)

6 AB

4. The reciprocal of the resistance is__________

(a)

conductance

(b)

conductivity

(c)

resistivity

(d)

specific resistance

5. A circular coil of radius 5 cm and 50 turns carries a current of 3 ampere. The magnetic dipole moment of the coil is

(a)

1.0 amp – m2

(b)

1.2 amp – m2

(c)

0.5 amp – m2

(d)

0.8 amp – m2

6. Th ree wires of equal lengths are bent in the form of loops. One of the loops is circle, another is a semi-circle and the third one is a square. Th ey are placed in a uniform magnetic fi eld and same electric current is passed through them. Which of the following loop confi guration will experience greater torque ?

(a)

circle

(b)

semi-circle

(c)

square

(d)

all of them

7. In electric power transmission, the wastage of power is

(a)

more at high voltages

(b)

independent of voltage

(c)

more at low voltage

(d)

low at low voltages

8. In LCR circuit when KL = Xc (at resonance) the current _________________

(a)

is zero

(b)

is in phase with the voltage

(c)

(d)

lags behind the voltage

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. The wavelength range of microwave is _______m

(a)

10-8 to 0.35

(b)

10-3 to 0.3

(c)

10-8 to 10-6

(d)

10-3 to 10-1

11. A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is, [take wavelength of light, λ = 500 nm]

(a)

1 m

(b)

5 m

(c)

3 m

(d)

6 m

12. The work functions for metals A, B and C are 1.92 eV, 2.0 eV and 5.0 eV respectively. The metals which will emit photoelectrons for a radiation of wavelength 4100$\\ \\ \mathring { A } \\$ is/are

(a)

A only

(b)

both A and B

(c)

all these metals

(d)

none

13. The ratio between the first three orbits of hydrogen atom is

(a)

1:2:3

(b)

2:4:6

(c)

1:4:9

(d)

1:3:5

14. Doping a semiconductor results in

(a)

The decrease in mobile charge carriers

(b)

The change in chemical properties

(c)

The change in the crystal structure

(d)

The breaking of the covalent bond

15. Which one of the following is the natural nanomaterial

(a)

Peacock feather

(b)

Peacock beak

(c)

Grain of sand

(d)

Skin of the Whale

16. Part B

Answer any SIX questions. Question number 24 is compulsory

6 x 2 = 12
17. Write down Coulomb’s law in vector form and mention what each term represents.

18. What is the electric flux through a cube of side 1cm which encloses on electric dipole?

19. Define magnetic flux.

20. A bar magnet is moved in the direction indicted by the arrow between two coils PQ and CD predict the directions of induced current in each coil.

21. What are electromagnetic waves?

22. What is wave theory of light?

23. What are thermal neutrons? Why are neutrons considered as ideal particles for nuclear fission?

24. Give circuit symbol, logical operation, truth table, and Boolean expression of AND, OR, NOT, NAND, NOR, and EX-OR gates

25. What does RADAR stand for?

26. Part C

Answer any Uquestions. Question number 33 is compulsory

6 x 3 = 18
27. If the resistance of coil is 3 Ω at 20oC and α = 0.004/oC then determine its resistance at 100oC.

28. Calculate the magnetic induction at a point on the axial line of a bar magnet.

29. In a certain region of space, electric field $\vec { E }$ and magnetic field $\vec { B }$ are perpendicular to each other. An electron enters in the region perpendicular to the direction of both $\vec { B }$ & $\vec { E }$ and moves undeflected. Find the velocity of electron.

30. A variable frequency ac source is connected to capacitor. How will the displacement current change with decrease in frequency.

31. Explain experimentally observed facts of photoelectric effect with the help of Einstein's explanation.

32. Write the properties of neutrino?

33. Elaborate on the basic elements of communication system with the necessary block diagram.

34. What happens when and electric dipole is held in a non-uniform electric field?

35. Calculate the equivalent resistance for the circuit which is connected to 24 V battery and also find the potential difference across 4 Ω and 6 Ω resistors in the circuit.

36. Part D

5 x 5 = 25
1. The half-life of $_{ 38 }^{ 90 }{ Sr }$ is 28 years. What is the disintegration rate of 15mg of this isotope?

2. In the circuit shown in the figure, the input voltage Vi is 20 V, VBE = 0 V and VCE = 0 V. What are the values of IB, IC, β?

1. Calculate the distance for which ray optics is good approximation for an aperture of 5 mm and wavelength 500 nm.

2. Calculate the de Broglie wavelength of a proton whose kinetic energy is equal to 81.9 x 10-15J. (Given: mass of proton is 1836 times that of electron).

1. For the given capacitor configuration
(a) Find the charges on each capacitor
(b) potential difference across them
(c) energy stored in each capacitor

2. Estimate the average different speed of conduction electrons in a copper wire of crosssectional area 1.0 x 10-7 m2 carrying a current of 1.5 A. Assume the density of conduction electrons to be 9 x 1028 m-3.

1. A conductor of linear mass density 0.2 g m-1 suspended by two flexible wire as shown in figure. Suppose the tension in the supporting wires is zero when it is kept inside the magnetic field of 1 T whose direction is into the page. Compute the current inside the conductor and also the direction of the current. Assume g = 10 m s-2

2. The instantaneous voltage from an ac source is given by V = 300 sin 314t. What is the rms voltage of the sauce? Find its peak voltage and frequency of the sauce?

1. A magnetron in a microwave oven emits electromagnetic waves (em waves) with frequency f = 2450 MHz. What magnetic field strength is required for electrons to move in circular paths with this frequency?.

2. The magnetic field amplitude of an Electromagnetic wave is 1.6 x 10-7 T. If the frequency is 30 MHz. determine electric field, any velocity K and λ.