When a metallic surface is illuminated with radiation of wavelength $\lambda$, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2$\lambda$, the stopping potential is $\frac{V}{4}$ .The threshold wavelength for metallic surface is:

1. 5$\lambda$               
2. $\frac{5}{2}$$\lambda$
3. 3$\lambda$               
4. 4$\lambda$

An electron of mass m and a photon have the same energy E. Find the ratio of de-Broglie wavelength associated with the electron to that associated with the photon. (c is the velocity of light)

<sup>$1.$ ${\left(\frac{E}{2m}\right)}^{1/2}$

$2.$ $c{\left(2mE\right)}^{1/2}$

$3.$ $\frac{1}{c}{\left(\frac{2m}{E}\right)}^{1/2}$

$4.$ $\frac{1}{c}{\left(\frac{E}{2m}\right)}^{1/2}$</sup>
 

A radiation of energy 'E' falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (c=velocity of light)

1. E/c

2. 2E/c

3. 2E/c²

4. E/c²

Which of the following figures represents the variation of the particle momentum and the associated de-Broglie wavelength?

1.		2.
3.		4.

Light with a wavelength of $500$ nm is incident on a metal with a work function of  $2.28~\text{eV}.$ The de Broglie wavelength of the emitted electron will be:
1. $<2.8 \times 10^{-10}~\text{m}$
2. $<2.8 \times 10^{-9}~\text{m}$
3. $\geq 2.8 \times 10^{-9}~\text{m}$
4. $<2.8 \times 10^{-12}~\text{m}$

Light with an energy flux of $25\times 10^{4}~\text{Wm}^{-2}$ falls on a perfectly reflecting surface at normal incidence. If the surface area is $15~\text{cm}^2$, then the average force exerted on the surface is:
1. $1.25\times 10^{-6}~\text{N}$
2. $2.5\times 10^{-6}~\text{N}$
3. $1.2\times 10^{-6}~\text{N}$
4. $3.0\times 10^{-6}~\text{N}$