#### 12th Standard Physics Magnetism and magnetic effects of electric current English Medium Free Online Test One Mark questions 2020 - 2021

12th Standard

Reg.No. :
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Physics

Time : 00:20:00 Hrs
Total Marks : 20

20 x 1 = 20
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. 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)

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

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

(a)

M

(b)

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

(c)

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

(d)

$\frac { 1 }{ 2 } m$

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. Which of the following graphs shows the variation of magnetic induction B with distance 'r' from along wire carrying current?

(a)

(b)

(c)

(d)

8. Which one of the following represents corrent magnetic field lines?

(a)

(b)

(c)

(d)

9. A current carrying conductor is associated with

(a)

electric field

(b)

magnetic field

(c)

electro magnetic

(d)

all these

10. If a current I is flowing in a straight wire parallel to X-axis and magnetic field is in y-axis then the wire experiences

(a)

in Z-direction

(b)

in Y- direction

(c)

no force

(d)

in X- diection

11. The unit of magnetic field is

(a)

ampere-turn

(b)

ampere

(c)

newton coulomb

(d)

tesla

12. A galvanometer coil has a resistance of 15Ω and gives full scale deflection for a current of 4mA. To convert it to an ammeter of range 0 to 6 amp.

(a)

10mΩ resistance is to be connected in parallel to the galvanometer

(b)

10mΩ resistance is to be connected in series with the galvanometer

(c)

0.1mΩ resistance is to be connected in series with the galvanometer

(d)

0.1mΩ resistance is to be connected in. parallel to the galvanometer

13. Fuse wire

(a)

is an alloy oflead and copper

(b)

has low resistance

(c)

has high resistance

(d)

has high melting point

14. According to Joule's heating effect the law of resistance is

(a)

H ∝ R

(b)

H ∝ R2

(c)

R ∝ H2

(d)

all the above

15. A 110 W, 220 V bulb draws a current

(a)

2 A

(b)

440 A

(c)

0.5 A

(d)

5.5 A

16. 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

17. Which one of the following pair of particles move with same velocity along the same circular path in a uniform magnetic field?

(a)

electron, proton

(b)

proton, deutron

(c)

proton, alpha particle

(d)

deutron, alpha particle

18. When the number of turns (n) in a galvanometer is doubled, current sensitivity

(a)

remains constant

(b)

decreases twice

(c)

increases twice

(d)

increases four times

19. Two T.G's having reduction factor K1 and K2 are connected series and give deflections θ1and θ2 respectively. Then K1 : K2

(a)

θ1 : θ2

(b)

tanθ1 : tanθ2

(c)

θ2 : θ1

(d)

tanθ2 : tanθ1

20. What is the current passing through a coil of radius of 8 cm having 50 turns, when a magnetic intensity at the centre of the coil is 125 A turns m-1?

(a)

0.1 ampere

(b)

0.4 ampere

(c)

1 ampere

(d)

4 ampere