Bestie needs help :)

[Bestie]

Why is it that only little current will travel through reverse bias?
And when considering that in a circuit , the diode is wired in reverse bias. If the emf of the supply is -2.5 V, what is the voltage drop across the diode? Justify your answer. isn't it just -2.5? not sure how to justify it though

Thank you in advance

[Bronzebottom64]

Ideally a diode in reverse bias has infinite resistance, this is an ideal and so will never be quite infinite however for the sake of VCE physics we can say that it has infinite resistance. This means the ratio of resistances for a reverse bias diode and any other resistor in series will cause the diode to use all of the emf voltage. Therefore yes, it will draw the full 2.5 V.

[Bestie]

ok thank you

[Bestie]

please help with this question...
how do you know if its analogue or digital?

thank you

[Stevensmay]

A digital signal has only two states, it is either on or off, there is no middle ground. When I measure the signal it will either be on or off.
http://3.bp.blogspot.com/-5O6-mIEbaZI/Ujat926DzwI/AAAAAAAAAOk/lkpmF4Z9taA/s1600/digital-signal.png

An analogue signal can have a much larger number of discrete values, and consequently will often form a sine wave. The information in an analogue signal is carried by the amplitude of the wave at a given time. When I measure a analogue signal, I can get many different values depending on the signal.


Since in your example we are overlaying an analogue signal onto an analogue data stream, we will end up with a analogue signal output.
Essentially match the signal you are given to one of these and you will have your answer.

[Bestie]

thank you stevensmay

could you please help me on this one as well, or anyone else? thank you

[Stevensmay]

The device will produce a signal whenever it detects light. Since there is a delay in how long it takes to detect it, whenever a light pulse occurs, it will be 15 microseconds before the detector realises it and outputs a signal.

Sorry for the not great explanation, I'll have my laptop around 8 so can write a better one then.

[Bestie]

yes please

[Stevensmay]

Irrelevant to the question but let's identify the type of signal we have. Since the light intensity is only observed in two states, bright and dark, we can say it is a digital signal.

Onto the actual question. When exposed to a light source, the opto-electronic device will output a voltage. We do not know the magnitude of the output, but the question tells us we do not have to give voltage values so we are fine. Essentially, whenever it is light the opto-electronic device will be producing a voltage.

[Bestie]

but then how come the ans looks like:

[Stevensmay]

My apologies Bestie, I interpreted response time differently. What they are describing in the answer I would have thought was considered rise and fall time, not response. Could someone verify this please?