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PHYSICS > Dual Nature Of Radiations And Matter > Flashcards

Dual Nature Of Radiations And Matter Flashcards

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1
Q

Cathode Ray was discovered by?

A

William crookes

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2
Q

How was cathode rays discovered ?

A

When electric field was applied to the gas in a discharge tube,a flourescent glow appeared on the glass opposite to cathode,William crookes suggested that these consists of streams of fast moving negetively charged particle

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3
Q

Who discovered the e/ m ratio?

A

J J Thomson

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4
Q

How was e/ m ratio discovered

A

e/ m ratio discovered by applying mutually perpendicular electric and magnetic field across the discharge tube.

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5
Q

3 Rd observation ?

A

When certain metals were irradiated by ultraviolet light or heated at high temperatures were found to emit negetively charged particle having same e/m ration as that of cathode ray particles

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6
Q

Who named the particles electron?

A

J J Thomson

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7
Q

Who established that electric charge is quantised?

A

RA Millikan bu oil drop experiment, found the charge of electrons as 1.6 ×10^-19C

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8
Q

What is electron emission?

A

If na electron attempt to come out of the metal ,the metal acquires positive charge and pulls the electron back ,the electron can come out of the metal only if it got sufficient energy to overcome the attractive pull

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9
Q

Work function?

A

The minimum energy required to eject an electron from a metal is called work function.

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10
Q

Work function is denoted by?

A

∅° ( phi 0)

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11
Q

Work function is measured in ?

A

eV

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12
Q

Work function depends on?

A

1) properties of metal
2) nature of its surface

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13
Q

One electron volt?

A

Energy gained by an electron when it has been accelerated by a potential difference of one volt

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14
Q

1eV=

A

1.6×10^-19 J

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15
Q

Which metal has highest work function?

A

Platinum
5.65 eV

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16
Q

Which metal has lowest work function?

A

Ceasium
2.14 eV

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17
Q

The minimum energy required for electron emission ( work function) can be supplied to free electrons by?

A

1) THERMIONIC EMISSION

2) FIELD EMISSION

3) PHOTO -ELECTRIC EMISSION

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18
Q

THERMIONIC EMISSION

A

By suitably heating the electron will get sufficient thermal energy to escape from the metal surface

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19
Q

Field emission

A

By applying very strong electric field ( in the order of 10⁸ V/m ) to a metal.the electron will get sufficient energy to escape from the metal ,as in a spark plug.

20
Q

PHOTO-ELECTRIC EMISSION

A

When light of suitable frequency is incident on a metal surface electrons are ejected from the metal surface ,the photo generated electrons are called photo electrons

21
Q

Photo electric emission was discovered by

A

Heinrich Hertz

22
Q

What did he observe ( Heinrich Hertz?

A

He observed that when light falls on a metal surface the electron escaped from surface of metal tk surrounding space

23
Q

What was lenard’s observation ?

A

When uv rays were allowed to fall on emitter plate of an evacuated glass tube enclosing two electrodes , current flows in the circuit.

24
Q

Hallwach’s observation ?

A

He connected a negetively charged zin plate to an electroscopes and found that negetively charged particle were emitted from the zinc plate under the action of uv light

25
Q

Zinc, cadmium , magnesium responded to uv rays with _____ to cause electron emission from the surface?

A

1) short wavelength
2) high frequency
3) high energy

26
Q

Wha uv rays neede. For electron emission from alkali metal such as lithium ,rubidium , ceasium , sodium , potassium?

A

No they were sensitive to even visible light

27
Q

Photo electric effect?

A

The phenomenon of emission of electrons when photosensitive substance are illuminated by light of suitable frequency

28
Q

Experimental study of photo-electric effect ?

A

REFER NOTE

29
Q

Effect of intensity of light on photocurrent

A

When the intensity of incidents radiation is increased keeping the frequency and accelerating potential fixed ,the no.of photoelectrons emitted increase , therefore photo-electric current also increases

The photo electric current increases linearly with incident light ( straight line with a slope)

The photo electric current and intensity of light is directly proportional

30
Q

Effect of potential on photo-electric current .

A

When the positive potential of collector A is increased the photo electric current increases untill all the electrons are colled by the collector,then the photo electric current becomes maximum and is called the SATURATION CURRENT

when the collector plate is made negetive with respect to emitter plate C ,the photo electric current decreases with an increase in negetive potential and finally Becomes zero
The minimum negetive potential for collector plate when photo-electric current stops or becomes zero is called cut- off/stopping potential.

31
Q

At stopping potential?
( Expression)

A

REFER NOTE

32
Q

Effect of intensity of incidents radiation on stopping potential.m

A

The experiment is repeated with incident radiation of constant frequency but different intensity I¹,I²,I³ ,as the intensity increases the photo electric emission increases which increases the saturation current , but as the kinetic is constant stopping potential is also constant

Ie, FOR A GIVEN FREQUENCY OF INCIDENT RADIATION, STOPPING POTENTIAL IS INDEPENDENT OF INTENSITY OF INCIDENT RADIATION

33
Q

Effect of frequency of incident radiation on stopping potential

A

The experiment is repeated with same intensity but different frequencies such that V3>V2>V1
as the frequency increase,K E increase stopping potential also increases , intensity reamins same , therefore the no change in saturation current.

ie,as frequency of incidents radiation increases , stopping potential increase

34
Q

Threshold frequency

A

Threshold frequency is the minimum cut off frequency below which the photo electric emission does not take plac e no matter how intense the incident light is .

35
Q

Wave theory is unable to explain basic features like ?

A

1) according to the wave picture of light ,the free electrons at the surface of metals absorb the radiant energy continuously , therefore larger the intensity of incidents radiation ,largest should be the radiant energy absorbed by the free electrons which is contradictory to the observation of photoelectric effect.
2)as large number of electrons absorb energy , energy absorbed by a single electron per unit time is very small ,so it might take hours or more to aquire sufficient energy to overcome work function this is contradictory to the observation the photo-electric emission is instantaneous

36
Q

Einstein’s photoelectric equation:Energy quantum of radiation

A

When a photon incident on a metal surface ,part of its energy is used a work function and the remaining part is used to give KE to emitted photoelectrons

Refer note

37
Q

Variation of stopping potential with frequency of incident radiation

A

Refer note

38
Q

Particle nature of light

A

1) in the interaction of light with matter it behaves as if it is made up of particles called photon
2) each photon has the
.energy= hv
. momen p = hv/c
.c=3×10⁸m/s
Whatever the intensity of the radiation be
3) all photons of particular wavelength ior frequency have the same energy and momentum whatever the intensity may be
4) as the intensity of incidents radiation increases,no of photons increases , energy is independent of intensity of light
5) photons are electrically neutral they are not deflected by electric or magnetic field
6) In photon - particle collision total energy and total momentum is conserved but no of photons may not be. Conserved as the photons could be absorbed or new photons may be created.

39
Q

Monochromatic light of frequency 6.0 ×1014 Hz is produced by a laser. The
power emitted is 2.0 ×10–3 W.
(a) What is the energy of a photon in the light beam?
(b) How many photons per second, on an average, are emitted by the
source?

A

(a) Each photon has an energy E = h ν = 6.63 ×10–34x6.0 ×1014 Hz
= 3.98 × 10–19 J
(b)N=power/Energy=5 x10^15photons per second

40
Q

The work function of a metal is 6eV. If two photons each having energy 4 eV
strike the metal surface. Will the emission be possible? Why?

A

No, photo emission is not possible.
Photo emission is possible only if ℎ𝑣 > 𝜙0
Here energy of incident photon is less than work function
and hence photo emission is not possible.

41
Q

The work function of caesium is 2.14 eV.
a) Find the threshold frequency for caesium.
b) the wavelength of the incident light if the photocurrent is brought
to zero by a stopping potential of 0.60 V.

A

𝑣0= 𝜙0/h
𝜙0 =2.14 eV =2.14 x1.6x10-19 J
h=6.63 x10-34J/s
=
=5.16 x1014 Hz
B) refernote

42
Q

Wave nature of matter?

A

Wave Nature of Matter
▪
The wave nature of light shows up in the phenomena of
interference, diffraction and polarisation. On the other hand, in
photoelectric effect and Compton effect which involve energy and
momentum transfer, radiation behaves as if it is made up of particles –
the photons.
▪
The gathering and focussing mechanism of light by the eye-lens is
well described in the wave picture. But its absorption by the rods and
cones (of the retina) requires the photon picture of light.

43
Q

A natural question arises: If radiation has a dual (wave-particle) nature,
might not the particles of nature (the electrons, protons, etc.) also exhibit
wave-like character?

A

Louis Victor de Broglie argued that moving particles of matter should
display wave-like properties under suitable conditions.
As nature is symmetrical , the two basic physical entities of nature – matter
and energy, must have symmetrical character. If radiation shows dual
aspects, matter should also exhibit dual nature.

44
Q

De broglies relation

A

Refer note

45
Q

Laws of photoelectric effect?

A

i.For a given photosensitive material and frequency of incident radiation,
the photoelectric current is directly proportional to the intensity of
incident light.
ii.For a given photosensitive material and frequency of incident radiation,
saturation current is found to be proportional to the intensity of incident
radiation whereas the stopping potential is independent of its intensity .
iii.For a given photosensitive material, there exists a certain minimum cutoff frequency of the incident radiation, called the threshold frequency(𝑣0)
below which no emission of photoelectrons takes place, no matter how
intense the incident light is. Above the threshold frequency, the stopping
potential or equivalently the maximum kinetic energy of the emitted
photoelectrons increases linearly with the frequency of the incident
radiation, but is independent of its intensity
iv.The photoelectric emission is an instantaneous process without any
apparent time lag.

46
Q

THERMIONIC EMISSION
Depends on

A

. temperature
.nature of work function of metal
. nature of surface of metal

47
Q

Thermal energy generated electrons are called

A

Thermions

PHYSICS (1 decks)

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