What

factor can be a problem for bipolar junction transistors?

An NPN bipolar junction transistor has an Emitter donor

doping concentration of

Calculate the (\beta \) gain that you would expect from the

transistor, rounding your answer to three significant figures if necessary.

A bipolar junction transistor with

operates

with a collector current of

Calculate the emitter current (

), stating your answer

in

Which region of a p-n junction photodiode most efficiently generates

charge carriers when exposed to light?

One of the effects of pollution is the gradual build-up of layers

of grime on surfaces.  You are

investigating how this affect the performance of solar cells.  After one month without rain, you find that a

layer of grime with thickness

Plank’s constant , the speed of light

and the proton charge

Calculate the fraction of light that penetrates to the

solar cell through the grime (the ratio of the light intensity with the grime layer

and the light intensity of a solar cell when

State your answer as a decimal fraction, rounding to two

decimal places if necessary.

If a photodiode is operated as a photovoltaic cell, what

can it be used for?

A photon has a wavelength of . 

Plank’s constant , the speed of light

and the

proton charge

Calculate the energy of the photon in eV, stating your

answer to 2 decimal places.

Light of energy

shines onto an

area

Plank’s constant , the speed of light

and the

proton charge

Calculate the photocurrent in the photoconductor assuming

all photons are absorbed.  State your

answer in mA, rounding to the nearest integer value if necessary.

If a photodiode is operated as a photodetector, what

can it be used for?