#### 12th Standard Physics English Medium Magnetism and Magnetic Effects of Electric Current Reduced Syllabus Important Questions 2021

12th Standard

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 105

Multiple Choice Questions

15 x 1 = 15
1. The magnetic fi eld at the center O of the following current loop is

(a)

$\frac { { \mu }_{ ° }I }{ 4r } \bigotimes$

(b)

$\frac { { \mu }_{ ° }I }{ 4r } \bigodot$

(c)

$\frac { { \mu }_{ ° }I }{ 2r } \bigotimes$

(d)

$\frac { { \mu }_{ ° }I }{ 2r } \bigodot$

2. An electron moves straight inside a charged parallel plate capacitor of uniform charge density σ. Th e time taken by the electron to cross the parallel plate capacitor when the plates of the capacitor are kept under constant magnetic fi eld of induction $\vec { B }$is

(a)

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

(b)

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

(c)

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

(d)

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

3. 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

4. A wire of length l carries a current I along the Y direction and magnetic field is given by $\vec { B } =\frac { \beta }{ \sqrt { 3 } } =(\hat { i } +\hat { j } +\hat { k } )T.$ The magnitude of Lorentz force acting on the wire is

(a)

$\sqrt { \frac { 2 }{ \sqrt { 3 } } } \beta Il$

(b)

$\sqrt { \frac { 1 }{ \sqrt { 3 } } } \beta Il$

(c)

$\sqrt { 2 } \beta Il$

(d)

$\sqrt { \frac { 1 }{ 2 } } \beta Il$

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. The vertical component of Earth’s magnetic field at a place is equal to the horizontal component. What is the value of angle of dip at this place?

(a)

30°

(b)

45°

(c)

60°

(d)

90°

7. A current carrying conductor is associated with

(a)

electric field

(b)

magnetic field

(c)

electro magnetic

(d)

all these

8. Direction of magnetic force on a positive charge moving in a magnetic field is given by

(a)

thumb rule

(b)

left hand rule

(c)

right hand rule

(d)

cork screw rule

9. Consider the motion of a charged particle in a uniform magnetic field directed into the paper. If velocity v of the particle is in the plane of the paper, the charged particle will describe a

(a)

straight line

(b)

circle

(c)

ellipse

(d)

hyperbola

10. The direction of magnetic field close to a straight conductor carrying current will be

(a)

along the length of the conductor

(b)

(c)

circular in a plane perpendicular to the conductor

(d)

helical

11. According to Joule's heating effect the law of time is

(a)

H ∝ T2

(b)

T ∝ H2

(c)

both (a) and (b)

(d)

$\frac{H}{t}$ =constant

12. Joule's heating effect and Peltier effect are proportional to the

(a)

square and cube respectively of the current

(b)

square and the first power, respectively of the current

(c)

square of the current

(d)

current

13. The magnetic induction at the center of a circular coil carrying current is

(a)

$\frac { \mu nI }{ 2a }$

(b)

$\frac { \mu I }{ 2\pi a }$

(c)

$\frac { \mu I }{ 2na }$

(d)

$\frac { \mu I }{ 2na }$

14. The ratio of magnetic length and Geometrical length is _______

(a)

$\frac { 4 }{ 5 }$

(b)

$\frac { 5 }{ 6 }$

(c)

$\frac { 6 }{ 5 }$

(d)

$\frac { 5 }{ 4 }$

15. The magnitude of the magnetic Lorentz force does not depend on ______

(a)

mass of the charged particle

(b)

velocity of the charged particle

(c)

magnetic induction

(d)

direction of motion of the charged particle

16. 2 Marks

10 x 2 = 20
17. What is meant by magnetic induction?

18. State Biot-Savart’s law.

19. State Ampere’s circuital law.

20. What are the causes for earth's magnetic field according to Gover?

21. What is Magnetic field?

22. Define magnetic flux density.

23. Write the Similarities between Coulomb's law and Biot-Savort's law.

24. What is magnetic Lorentz force?

25. Why the Phosphor - bronze wire is used as the suspension wire in moving coil galvanometer?

26. . Explain the concept of velocity selector.

27. 3 Marks

10 x 3 = 30
28. The horizontal component and vertical components of Earth’s magnetic field at a place are 0.15 G and 0.26 G respectively. Calculate the angle of dip and resultant magnetic field.

29. The repulsive force between two magnetic poles in air is 9 x 10-3 N. If the two poles are equal in strength and are separated by a distance of 10 cm, calculate the pole strength of each pole.

30. Deduce the relation for the magnetic induction at a point due to an infinitely long straight conductor carrying current.

31. What is tangent law? Discuss in detail.

32. Explain the principle and working of a moving coil galvanometer.

33. Mention the properties of Magnetic field lines?

34. Tabulate the difference between Coulomb's law and Biot-Savort's law.

35. Write the expression in a vector from for the (i) Lorentz magnetic force $\vec { F }$ due to a charge moving with velocity $\vec { v }$ in a magnetic field $\vec { B }$ What is the direction of force. (ii) If the magnetic force $\vec { F }$ acting an it is non-zero would the particle gain any energy?

36. Magnetic field lines can be entirely confined within the core of toroid, but not within a straight solenoid. Why?

37. Two identical charged protrudes moving with the same speed enter a region of uniform magnetic field. If one of these enters normal to the field direction and the other enters along a direction at 30° with the field. What would be the ratio of their angular frequencies.

38. 5 Marks

8 x 5 = 40
39. An electron moving perpendicular to a uniform magnetic field 0.500 T undergoes circular motion of radius 2.80 mm. What is the speed of electron?

40. A proton moves in a uniform magnetic field of strength 0.500 T magnetic field is directed along the x-axis. At initial time,
t =0s, the proton has velocity
$\hat { v } =(1.95\times { 10 }^{ -5 }\hat { i } +2.00\times { 10 }^{ 5 }\hat { k } )m{ s }^{ -1 }$
(a) At initial time, what is the acceleration of the proton.
(b) Is the path circular or helical?. If helical, calculate the radius of helical trajectory and also calculate the pitch of the helix (Note: Pitch of the helix is the distance travelled along the helix axis per revolution).

41. A circular coil with cross-sectional area 0.1 cm2 is kept in a uniform magnetic field of strength 0.2 T. If the current passing in the coil is 3 A and plane of the loop is perpendicular to the direction of magnetic field. Calculate
(a) total torque on the coil
(b) total force on the coil
(c) average force on each electron in the coil due to the magnetic field of the free electron density for the material of the wire is 1028 m-3.

42. Calculate the magnetic field at the center of a square loop which carries a current of 1.5 A, length of each loop is 50 cm.

43. Explain the Motion of a charged particle in a uniform magnetic field.

44. Two identical coils P & Q each of radius Rare lying in perpendicular planes such that they have a common centre. Find the magnitude and direction of magnetic field at the common centre of the two coils. if they currents equal to I and $\sqrt{2}$ Irespectively.

45. The length of a solenoid is 0.2m and it has 120 turns. Find the magnetic field in its interior if a current of 2.5 A is flowing through it.

46. A circular coil of 20 hours and radius 10cm is placed in an uniform magnetic field of 0.17 normal to the plane of the coil if the current in the coil is 5.0A. What is the (i) total torque on the coil, (ii) total force on the coil (iii) average force on each electron in the coil due to the magnetic field? The coil is made of copper wire of cross - (a) sectional area 10-5 m+2 and the free electron density in copper is given to be about 1029/m3)