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#### 12th Standard Physics English Medium Free Online Test 1 mark questions 2020 - Part Ten

12th Standard EM

Reg.No. :
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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
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. The time taken by a conductor to reach electrostatic equilibrium is in the order of

(a)

10-18

(b)

10-14s

(c)

10-16 s

(d)

10-20 s

3. The force between like charges is _________.

(a)

attraction

(b)

repulsion

(c)

no force

(d)

none

4. A carbon resistor of (47 ± 4.7 ) k Ω to be marked with rings of diff erent colours for its identifi cation. Th e colour code sequence will be

(a)

Yellow – Green – Violet – Gold

(b)

Yellow – Violet – Orange – Silver

(c)

Violet – Yellow – Orange – Silver

(d)

Green – Orange – Violet - Gold

5. The equivalent resistance between A and Bin the figure is

(a)

$15\Omega$

(b)

$7.5\Omega$

(c)

$25\Omega$

(d)

$30\Omega$

6. Kirchhoff's law is applicable only for__________

(a)

simple circuits

(b)

primary circuits

(c)

complicated circuits

(d)

secondary circuits

7. 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)

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

8. Two short bar magnets have magnetic moments 1.20 Am2 and 1.00 Am2 respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards the south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centers is (Horizontal components of Earth’s magnetic induction is 3.6 x 10-5 Wb m-2 )

(a)

3.60 × 10-5 Wb m-2

(b)

3.5 × 10-5 Wb m-2

(c)

2.56 × 10-4 Wb m-2

(d)

2.2 × 10-4 Wb m-2

9. If the temperature of hot junction is increased beyond inversion temperature the thermo emf

(a)

is constant

(b)

increases

(c)

decreases

(d)

becomes zero

10. The orbital magnetic moment of an electron in the second orbit (n = 2) is

(a)

18.54 x 10-24 Am2

(b)

18.54 x 10-34 Am2

(c)

19.44 x 10-34 Am2

(d)

19.44 x 10-24 Am2

11. The quantity that changes with time in an A.C current is

(a)

magnitude

(b)

direction

(c)

both magnitude and direction

(d)

none

12. During the propagation of electromagnetic waves in a medium

(a)

electric energy density is double of the magnetic energy density

(b)

electric energy density is half of the magnetic energy density

(c)

electric energy density is equal to the magnetic energy density

(d)

both electric and magnetic energy densities are zero

13. Carbon arc produces ________ spectrum.

(a)

characteristic

(b)

line

(c)

band

(d)

continuous

14. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index,

(a)

less than one

(b)

less than that of glass

(c)

greater than that of glass

(d)

equal to that of glass

15. An object is placed at 20 cm from a convex mirror of focal length 10 cm. The image formed by the mirror is

(a)

Real and 20 cm from the mirror

(b)

Virtual and at 20 cm from the mirror

(c)

Virtual and 20/3 cm from the mirror

(d)

Real and 20/3 cm from the mirror

16. Two photons. each of energy 2.5 eV are simultaneously incident on the metal surface. If the work function of the metal is 4.5 eV then from the surface of the metal

(a)

one electron will be emitted

(b)

two electrons will be emitted

(c)

more than two electrons will be emitted

(d)

not a single electron will be emitted

17. Electron microscope works on the principle of

(a)

photoelectron effect

(b)

particle nature of electron

(c)

wave nature of moving electron

(d)

dual nature of matter

18. If the kinetic energy of photo electron is found to be 16 J, whose mass is me, the maximum velocity of that electron will be

(a)

4$\sqrt { \frac { 2 }{ { m }_{ e } } }$

(b)

$\sqrt { 4{ m }_{ e } }$

(c)

$\sqrt { \frac { 4 }{ { 2 }m_{ e } } }$

(d)

$\sqrt { \frac { 1 }{ { m }_{ e } } }$

19. In an electron microscope, the electron beam is associated through a large potential difference in a device called _______

(a)

accelerator

(b)

electron gun

(c)

CRO

(d)

vibrator

20. The momentum for a wavelength of 0.01 Å is _________

(a)

6.626 x 10-22 kgm/s

(b)

5 x 10-24 kgm/s

(c)

6.5 x 10-23 kgm/s

(d)

7.2 x 10-34kgm/s

21. In J.J Thomson e/m experiment, a beam of electron is replaced by that of muons (particle with same charge as that of electrons but mass 208 times that of electrons). No deflection condition is achieved only if

(a)

B is increased by 208 times

(b)

B is decreased by 208 times

(c)

B is increased by 14.4 times

(d)

B is decreased by 14.4 times

22. For hydrogen atom, the energy of the nth orbit is given by, En =

(a)

$\frac { 13.6 }{ { n }^{ 2 } } eV$

(b)

0.53 n2 eV

(c)

$\frac { -13.6 }{ { n }^{ 2 } } eV$

(d)

3 n2 eV

23. If the distance between the conduction band and valence band is leV, then this combination is

(a)

semiconductor

(b)

metal

(c)

insulator

(d)

conductor

24. The output transducer of the communication system converts the radio signal into ________.

(a)

Sound

(b)

Mechanical energy

(c)

Kinetic energy

(d)

None of the above

25. Audio signal cannot be transmitted because

(a)

the signal has more noise

(b)

the signal cannot be amplitude for distance communication

(c)

the transmitting antenna length is very small to design

(d)

the transmitting antenna length is very large and impracticable