Question

The collector of the photocell (in photoelectric experiment) is made of tungsten while the emitter is of platinum having work function of $10 eV$. Monochromatic radiation of wavelength $124\mathring{A}$ and power 100 watt is incident on emitter which emits photo electrons with a quantum efficiency of $1 \% .$ The accelerating voltage across the photocell is of 10,000 volts (Use : $h _{ c }=12400 eV \mathring{A}$)

If the source of monochromatic radiation of wavelength $124\mathring{A}$has an efficiency of $50 \%,$ and the power of X-ray emitted by the tungsten target is $3 W$, the overall efficiency of the apparatus for X-ray production is

• A. $1 \%$
• B. $0.1 \%$
• C. $1.5 \%$
• D. $0.67 \%$

Answer 1

Answer: (A)

Power provided by accelerating potential $=100 W$
Power consumed by the source of
$124\mathring{A}=\frac{100}{(0.5)}=200 W$
Overall efficiency
$=\frac{\text { net power of } X-\text { ray }}{\text { net power supplied }}$
$=\frac{3 W}{100 W +200 W }$
$=0.01=1 \%$