Understanding DC Load Line and its Relationship with VCE & IC

[Pushoam]

I didn't understand the following:
The relationship between $V_{CE}$ and $I_C$ is linear.

In active region, even if the $V_{CE}$ increases, $I_C$ remains almost same for a given $I_B$. So, how can the relation between the two can be linear?

Can anyone tell me the utility of the d.c. load line?
What I lknow is for a faithful amplification, if the Q- point is taken as the midpoint of the d.c.load line, then we will get the desired output.

Is the concept of load line used only for BJT?

 

[cnh1995]

In active region, even if the VCEVCEV_{CE} increases, ICICI_C remains almost same for a given I_B. So, how can the relation between the two can be linear?

This is what the horizontal lines in the graph represent. The slant line describes the relation between I_C and V_CE as I_B is varied (in the active region) and V_cc is kept constant. Hence, for smaller I_B, I_c is also small which means V_CE is large. As I_B goes on increasing, I_c increases as well and V_CE decreases.

Can anyone tell me the utility of the d.c. load line?
What I lknow is for a faithful amplification, if the Q- point is taken as the midpoint of the d.c.load line, then we will get the desired output.

Is the concept of load line used only for BJT?

Load line is used to set the Q point, which is almost the midpoint of the load line. From the above graph, you can see the variation in output voltage w.r.t. variation in base current. This midpoint operation prevents the transistor from going into cutoff or saturation regions and the output waveform is linearly amplified (faithful operation).

Is the concept of load line used only for BJT?

It can be used for all the components, but I've seen it being used mostly for non-linear loads.

 

[Pushoam]

The slant line describes the relation between IC and VCE as IB is varied (in the active region) and Vcc is kept constant.

This is what I missed. Thank you for helping me.

But even if $I_B$ is varied, $I_C$ is not proportional to $V_CE$.
Setting Q-point means?
Does it mean that for a desired value of $I_C$ and $V_CE$ such that $I_C$ is proportional to $V_{CE}$, the load line helps to determine the input current i.e. the base current?