NEET Physics : Dual Nature of Radiation and Matter

Assertion: When a certain wavelength of light fall on a metal surface it ejects electron. 

Reason: Light has wave nature.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

The graph $\frac{1}{\mathrm{\lambda }}$ and stopping potential (V) of three metals having work function ${\mathrm{\varphi }}_1 , {\mathrm{\varphi }}_2 \mathrm{and} {\mathrm{\varphi }}_3$ in an experiment of photoelectric effect is plotted as shown in the figure. Which one of the following statement is/are correct? [Here λ is the wavelength of the incident ray ]

(i) Ratio of work functions  = 1 : 2 : 4

(ii) Ratio of work functions ${\mathrm{\varphi }}_1 : {\mathrm{\varphi }}_2 : {\mathrm{\varphi }}_3$ = 4 : 2 : 1

(iii) tanθ ∝ $\frac{\mathrm{h} \mathrm{c}}{\mathrm{e}}$, where h = Planck's constant, c = speed of light

(iv)The violet colour-light can eject photoelectrons from metals 2 and 3

• (i), (iii)

• (i), (iv)

• (ii), (iii)

• (i), (ii) and (iv)

Work function of a metal is 5.2 x 10^-18, then its threshold wavelength will be

• 736.7 A^o

• 760.7 A^o

• 301 A^o

• 344.4 A^o

Assertion:  As work function of a material increases by some mechanism, it requires greater energy to excite the electrons from its surface.

Reason:  A plot of stopping potential (V_s) versus frequency (v) for different metals, has greater slope for metals with greater work functions.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Photoelectric effect supports quantum nature of light because

• there is minimum frequency of light below which no photoelectrons are emitted

• the maximum energy of photoelectron depends only on the frequency of light and not on its intensity

• photoelectric effect is an instantaneous process

• all the above choices are correct

Light of two different frequencies whose photons
have energies 1 eV and 2.5 eV respectively, successively illuminate a metallic surface whose work function is 0.5 eV. Ratio of maximum speeds of emitted electrons will be

• 1 : 4

• 1 : 1

• 1 : 5

• 1 : 2

In photoelectric effect, the number of photo-electrons emitted is proportional to

• velocity of incident beam

• frequency of incident beam

• intensity of incident beam

• work function for cathode material

Which of the following has the longest de Broglie wavelength if they are moving with the same velocity?

• Neutron

• Proton

• $\mathrm{\alpha }$-particle

• β-particle

de-Broglie wavelength associated with a ball of mass 1 kg having kinetic energy 0.5 J is

• 6.63 × 10^-30 m

• 6.63 × 10^-34 m

• 1.32 × 10^-33 m

• 1.32 × 10^-34 m

An isotropic point source emits light with wavelength 500 nm. The radiation power of the source is P = 10 W . Find the number of photons passing through unit area per second at a distance of 3 m from the source.

• 5.92 x 10¹⁷ / m² s

• 2.23 x 10¹⁷ / m² s

• 2.23 x 10¹⁸ /m² s

• 5.92 x 10¹⁸ /m² s