$(a)$ Estimate the speed with which electrons emitted from a heated emitter of an evacuated tube impinge on the collector maintained at a potential difference of $500\;V$ with respect to the emitter. Ignore the small inttial speeds of the electrons. The specific charge of the electron, $i.e.$, the $e / m$ is glven to be $1.76 \times 10^{11}\; C\; kg ^{-1}$

$(b)$ Use the same formula you employ in $(a)$ to obtain electron speed for an collector potential of $10 \;MV$. Do you see what is wrong? In what way is the formula to be modified?

Monochromatic light of frequency $6.0 \times 10^{14}\,\, Hz$ is produced by a laser. The power emitted is $2 \times 10^{-3}\,\, W.$ The number of photons emitted, on the average, by the source per second is

Explain particle-wave (dual) nature of matter. 

If $c$ is the velocity of light in free space, the correct statements about photon among the following are:

$A$. The energy of a photon is $E=h v$.

$B$. The velocity of a photon is $c$.

$C$. The momentum of a photon, $p=\frac{h v}{c}$.

$D$. In a photon-electron collision, both total energy and total momentum are conserved.

$E$. Photon possesses positive charge.

Choose the correct answer from the options given below:

In a photo cell, the photo-electrons emission takes place