Dual Nature of Radiation and Matter

JEE Physics · 163 questions · Page 17 of 17 · Click an option or "Show Solution" to reveal answer

Q161

In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be:

A doubled

B halved

C Zero

D quadrupled

Correct Answer

Option C

Solution

Since

\frac{\mathrm{f}}{2} i.e. the incident frequency is less than threshold frequency. Hence there will be no emission of photoelectrons.

\Rightarrow \text { current }=0$$

Q162

The time taken by a photoelectron to come out after the photon strikes is approximately

{10^{ - 4}}\,s

{10^{ - 10}}\,s

{10^{ - 16}}\,s

{10^{ - 1}}\,s

Correct Answer

Option B

Solution

Emission of photo-electron starts from the surface after incidence of photons in about

{10^{ - 10}}s.

Q163

The ratio of de-Broglie wavelength of an

\alpha

particle and a proton accelerated from rest by the same potential is

\dfrac{1}{\sqrt m}

, the value of m is -

A 2

B 16

C 8

D 4

Correct Answer

Option C

Solution

Here : $m_\alpha=4 m_P, q_\alpha=2 q_P$ , potential $=V$ $\lambda=\dfrac{h}{\sqrt{2 m q V}}$ So, $\dfrac{\lambda_\alpha}{\lambda_P}=\sqrt{\dfrac{2 m_P q_P V}{2 m_\alpha q_\alpha V}}=\sqrt{\dfrac{m_P \cdot q_P}{4 m_P \times 2 q_P}}=\dfrac{1}{\sqrt{8}}$ $\Rightarrow$ $m=8$

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