" /> -->

#### Magnetism and Magnetic Effects of Electric Current Important Questions

12th Standard EM

Reg.No. :
•
•
•
•
•
•

Physics

Time : 01:00:00 Hrs
Total Marks : 50
5 x 1 = 5
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. 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

3. A thin insulated wire forms a plane spiral of N = 100 tight turns carrying a current I = 8 m A (milli ampere). The radii of inside and outside turns are a = 50 mm and b = 100 mm respectively.
The magnetic induction at the center of the spiral is

(a)

$5\mu T$

(b)

$7\mu T$

(c)

$8\mu T$

(d)

$10\mu T$

4. Four wires each of length 2m are bent into four loops P, Q, R and S and then suspended into uniform magnetic field as shown in the figure same current is passed in each loop. On which loop the couple will be the highest?

(a)

P

(b)

Q

(c)

R

(d)

S

5. A current carrying conductor is associated with

(a)

electric field

(b)

magnetic field

(c)

electro magnetic

(d)

all these

6. 5 x 1 = 5
7. Diamagnetic materials

8. (1)

Bi, Sb, Cu

9. Ferromagnetic materials

10. (2)

Steel, Alnico

11. Permanent magnets

12. (3)

To find the polarity of the solenoid

13. Right hand thumb rule

14. (4)

Fe, Ni, Co etc.,

15. End rule

16. (5)

Applied for circular coil carrying current

5 x 2 = 10
17. Define magnetic dipole moment.

18. What is magnetic susceptibility?

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

20. What is Geomagnetism?

21. What are the uses of studying hysteresis loops of various material.

22. 5 x 3 = 15
23. Let the magnetic moment of a bar magnet be $\overset { \rightarrow }{ { p }_{ m } }$ whose magnetic length is d = 2l and pole strength is qm. Compute the magnetic moment of the bar magnet when it is cut into two pieces
(a) along its length
(b) perpendicular to its length.

24. Two materials X and Y are magnetised, whose intensity of magnetisation are 500
A m-1 and 2000 A m-1, respectively. If the magnetising field is 1000 A m-1, then which
one among these materials can be easily magnetized?.

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

26. Obtain an expression for magnetic Lorentz force?

27. State the rule which is used to find the direction of field acting at a point near a current carrying street conductors?

28. 3 x 5 = 15
29. Show that for a straight conductor, the magnetic field
$\overset { \rightarrow }{ B } =\frac { { \mu }_{ ° }I }{ 4\pi a } (cos\varphi _{ 1 }-cos\varphi _{ 2 })\hat { n }$
$=\frac { { \mu }_{ ° }I }{ 4\pi a } (sin{ \theta }_{ 1 }+sin{ \theta }_{ 2 })\hat { n }$

30. Let E be the electric field of magnitude 6.0 × 106 N C-1 and B be the magnetic field
magnitude 0.83 T. Suppose an electron is accelerated with a potential of 200 V, will
it show zero deflection?. If not, at what potential will it show zero deflection.

31. A short bar magnet 0 magnetic field. It experiences a torque of 0.051 J.
(i) Calculate the magnitude of the magnetic field.
(ii) In which orientation will the bar magnet the in stable equilibrium in the magnetic field.