#### 12th Standard Physics Dual Nature of Radiation and Matter English Medium Free Online Test One Mark questions with Answer Key 2020 - 2021

12th Standard

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Physics

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

Answer all the questions

20 x 1 = 20
1. In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 kV, then the de Broglie wavelength associated with the electrons would

(a)

increase by 2 times

(b)

decrease by 2 times

(c)

decrease by 4 times

(d)

increase by 4 times

2. Two radiations with photon energies 0.9 eV and 3.3 eV respectively are falling on a metallic surface successively. If the work function of the metal is 0.6 eV, then the ratio of maximum speeds of emitted electrons will be

(a)

1:4

(b)

1:3

(c)

1:1

(d)

1:9

3. The mean wavelength of light from sun is taken to be 550 nm and its mean power is 3.8 × 1026W. The number of photons received by the human eye per second on the average from sunlight is of the order of

(a)

1045

(b)

1042

(c)

1054

(d)

1051

4. 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

5. The work function of a metal is hvo' Light of frequency v falls on this metal. The photoelectric effect will take: place only if

(a)

v<v0

(b)

v>2v0

(c)

v<v0

(d)

v>v0/2

6. If the frequency of light in a photoelectron experiment is doubled the stopping potential will

(a)

be doubled

(b)

be halved

(c)

become more than double

(d)

become less than double.

7. When the intensity of a light source is increased

(a)

the number of photons emitted by the source in unit time increases

(b)

more energetic photons are emitted

(c)

faster photons are emitted

(d)

total energy of the photons emitted per unit time decreases.

8. Stopping potential of emitted photo electrons is given by (where ф =hv0)

(a)

$\frac { hv-{ \phi }_{ 0 } }{ e }$

(b)

hv-ф

(c)

$\frac { hv }{ e }$

(d)

$\frac { hv+{ \phi }_{ 0 } }{ e }$

9. An electron of mass 'm' and charge 'e' accelerated from rest through a potential of V volt. then its final velocity is

(a)

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

(b)

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

(c)

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

(d)

$\sqrt { \frac { { 2V }_{ a } }{ m } }$

10. Louis de Broglie proposed the theory of _________

(a)

waves

(b)

matter waves

(c)

matter corpuscles

(d)

secondary wavelets

11. At the stopping potential, photoelectric current is _______

(a)

maximum

(b)

a constant

(c)

zero

(d)

infinity

12. ______ theory of light was proposed by Maxwell

(a)

Electromagnetic

(b)

Corpuscular

(c)

Wave

(d)

Quantum

13. The energy spent in releasing a photoelectron is called photoelectric _______ of the metal.

(a)

energy

(b)

ionization potential

(c)

work function

(d)

absorption energy

14. The cathode is coated with a material of low work function because ________

(a)

a large number of photo-electrons can be got

(b)

high work function should be achieved later

(c)

it is transparent

(d)

it is low in cost

15. Calculate the momentum of the particle of mass = 2g and velocity = 5.2 cm/s.

(a)

10.58 kgm/s

(b)

10.4 g cm/s

(c)

5.2 g cm/s

(d)

4.10 kgm/s

16. de- Broglie's concept confirms _______ postulate.

(a)

Bohr's

(b)

Newton's

(c)

Sommerfeld

(d)

Huygen's

17. Electron microscope employ magnetic lenses of _______ focal lengths to obtain large magnification.

(a)

short

(b)

long

(c)

infinite

(d)

zero

18. _______ is the only disadvantage of electron microscopes.

(a)

Operation only in high vacuum

(b)

Small size

(c)

High magnification

(d)

Cost

19. In Newtonian mechanics, mass, time, length and space were treated as ________

(a)

relative

(b)

absolute

(c)

variables

(d)

infinity

20. In classical mechanics, the time interval between two events has _______ value(s) for any two observers in motion.

(a)

different

(b)

zero

(c)

variable

(d)

same