What type of circuit u use?It would be useful for others to comment, if you got some circuit diagram that you are using.
Anyway, are u using 741 for voltage amplification? What configuration are u using?

Usually, when the difference of V+ and V- is zero, Vo should be zero(ideal). In some cases it is not zero, so you can use offset null (need to input some voltage in that pin) to make sure Vo is zero, when V+ minus V- is zero.

I dun think there is anything wrong with your circuit (just looked through), seem like inverting configuration. Most importantly, you need to get the data sheet of 741 and look for the minimum voltage need to be applied, to get the output. Try that.

I am not sure how much current is coming out of ur phototransistor ( you have to check the datasheet).
But what i can suggest is, u can maintain your configuration as shown in the diagram, but reduce the Rc value (resistor at collector) and put a new Re (resistor at emmiter) with higher value. In this way, voltage drop on Re wll go to your IC. Anyway, you can always use multimeter to check on the voltage level, when its bright and dark, and make a threshold value.

What type of amplifier you want to build??

I guess you mean Electrolytic capacitor and Ceramic capacitor.
There is only one significant difference between these two capacitors. Electrolytic capacitor should be connected by considering its polarity (the +ve and -ve terminal) but for ceramic polarity is not important (means you can connect which way you want to connect also).

For more info :- Try wiki Electrolytic capacitor

As in mathematically speaking, ceramic or electrolyte capacitor, we are just concerned about its capacitance, thats all.
Usually, in fact most of the time ceramic capacitors are lower capacitance.
So in that case, with low capacitance, high frequency signals can be filtered well (because the impedance of the capacitor will be large).

As you saying, it is very much depends on where you are using the capacitor.
As for simple audio applications, we do not need to be very particular, as the noise tolerance is limited by the user itself.
Of coz in high precision circuits, other factors such as temperature should be considered.

What type of capacitors you usually use in your design (i mean amplifiers)?

so that the all signal voltage will drop in the input of the amplifier. therefore no voltage is lost elsewhere.

Good question.
Well the diagram that you are referring is just the model representation of an op-amp circuit. That is not the real internal circuit of an op amp. You may look at the link here, to see the internal circuit

http://en.wikipedia.org/wiki/Image:OpAmpTr...red_Labeled.svg

To make our calculations easier, we tend to use the model of op-amp circuit.

Check your notes on relationship of emitter current to base current. rearrange the terms, you will get the prove

Normal shop does not provide you datasheets, you have to search for it.
Just google for it or register to www.farnell.com or www.rscomponents.com, and try searching in their database for datasheets.