Work done in isothermal vs adiabatic process If we include the sign then work done in adiabatic expansion as well as contraction is greater than the work done in isothermal process (as although area under $pV$ curve for isothermal process is greater than that for adiabatic process for expansion...work is negative area under curve ($\Delta V$ is positive) and for contraction work done in adiabatic process is anyhow greater)...then why do we say work done in isothermal expansion is greater? Does sign not matter? please help as soon as possible...my test is coming in a week.
 A: 
If we include the sign then work done in adiabatic expansion as well as contraction is greater than the work done in isothermal process

This is true for compression, not expansion. I'll get to this soon.
Isothermal processes follow $PV = constant$ while adiabatic processes follow $PV^{\gamma} = constant$ with $\gamma > 1$. We can therefore easily compare the two processes:

Clearly the area under the curve for isothermal processes is greater, so isothermal processes require more work.

Does sign not matter?

It does matter, but we compare absolute values when making claims like the "work done in isothermal expansion is greater."
For expansion, volume starts at $V_1$ and ends at some greater volume $V_2$. If you integrate the curves in the figure, you'll get positive work for both cases, meaning that work is performed on the surroundings. Clearly, $W_{isothermal} > W_{adiabatic}$ for expansion, meaning that an isothermal expansion does more work on the surroundings.
For compression, integrate the $PV$ curve from a larger volume $V_2$ to a smaller volume $V_1$. You'll have the same magnitudes of work as we did for expansion, but they are now negative. This means that work is input into the system. I think you're confused because $|W_{isothermal}| > |W_{adiabatic}|$ here (which is always true), but $W_{isothermal} < W_{adiabatic}$ since the adiabatic work is less negative. However, the isothermal compression requires more work to complete the process. When we say that isothermal compression requires more work, we mean that more work is input into the system (it is more negative).
A: Does sign not matter?
The sign simply tells us whether the system (say ideal gas) is performing work on the surroundings (positive work, where energy is transferred out of the system), or the surroundings are performing work on the system (negative work, where energy is transferred into the system).  In each case, the amount of work equals the magnitude of the energy transferred, regardless of whether it is positive or negative. In all cases the transfers are governed by the first law: $\Delta U=Q-W$.
If we include the sign then work done in adiabatic expansion as well as contraction is greater than the work done in isothermal process
From the graphs provided by @drew, if the system starts at the same equilibrium state and expands to the same final volume, you can clearly see that the positive isothermal work is greater than the positive adiabatic work since the area under the $pV$ curve is greater. The reason is the isothermal expansion process uses the heat transferred from the surroundings to do its work, whereas for the adiabatic expansion $Q=0$ and the process uses the system’s internal energy to perform its work.  This results in a greater drop in pressure for the adiabatic expansion to reach the final volume than that for the isothermal expansion, and thus less area under the $pV$ curve and less work. 
When the processes are reversed, the pressure rises at a faster rate for the adiabatic process (because all of the energy of the work done on the system increases its internal energy) than the isothermal process (because all of the energy of the work done on the system transfers out as heat). As a result, more negative work has to be done by the isothermal process to return to the same initial pressure as the adiabatic process. The adiabatic work may be less negative, but as previously stated, the amount of work depends only on its magnitude. 
Bottom line: The magnitude of the work for the isothermal process for both expansion and compression is greater than the magnitude of the work for the adiabatic process. Although the adiabatic compression work is less negative than the isothermal compression work, the amount of work depends only on its magnitude.
Hope this helps.
A: 
1. Expansion process:
The image on left is for expansion where the initial conditions are P1V1. We can imagine 2 containers of gas having same initial volume V1, pressure P1 and temperature T1 . 1st container is undergoing isothermal expansion. It takes heat from surrounding and the temperature remains constant throughout the cycle . 
The second container is insulated (No heat can be added/removed) in a adiabatic expansion.This will do less work than isothermal , because it solely depends on its internal energy to do work .This can be seen under the area of curves as well.
Compression process:
For compression we start both the process start at same point Vi(Volume) Pi(Pressure) Ti(Temperature)
Again if we consider 2 containers , the isothermal compression will take less effort to go from Vi to Vf , because it will give some heat to surroundings.The adiabatic compression will take lot of effort to go to final volume Vf . Hence you can see lot of pressure rise during the process.You can see the high pressure gradient in the right side graph (Adiabatic).
Summary
The initial condition needs to be same if we want to compare work done by the system (expansion) or work done on the system (compression) .
