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. $3.0\times 10^{-6}~\text{N}$

What will be the percentage change in the de-Broglie wavelength of the particle if the kinetic energy of the particle is increased to $16$ times its previous value?
1. $25$
2. $75$
3. $60$
4. $50$

A 200W sodium street lamp emits yellow light of wavelength $0.6 \mu m.$ Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is 

1. $1.5\times {10}^{20}$                               

2. $6\times {10}^{18}$

3. $62\times {10}^{20}$                                 

4. $3\times {10}^{19}$

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is:

1. $4\times {10}^{15}Hz$                               

2. $5\times {10}^{15}Hz$

3.$\mathrm{ 1}.6\times {10}^{15}Hz$                           

4. $2.5\times {10}^{15}Hz$