Understanding Resistance and Current in Ohmic and Non-Ohmic Components

[TreesGoBark]

Homework Statement

Homework Equations

V = IR

The Attempt at a Solution

For the first question, I understand that mathematically, the resistance is decreasing even though the graph is linear (R = V/I, and this ratio decreases with every increase in V). However, I don't understand why this is non-ohmic even if the graph is a linear one. Isn't point Vo the value of emf of the component? Why would having an emf (which shifts the graph to the right) make the resistance decrease? Also, why is option D wrong? (The answer is B).

For the second question, my reasoning for picking C is that by varying the resistance of the variable resistor, you can decide how much current to split into each branch (more resistance = less current into the variable resistor branch = more current into the lightbulb branch). However, the answer is A. I truly don't get this - wouldn't the lightbulb in A receive the same current no matter what the value of resistance of the variable resistor? Because even though the current splits up into the resistor branch and the variable resistor branch, they would join back together before reaching the lightbulb. [/B]

 

[phinds]

However, I don't understand why this is non-ohmic

It is non-ohmic because to achieve it you cannot use just a passive fixed resistor. You would have to use something like a zener diode in series with a fixed resistor. The resistor is ohmic but the total circuit isn't (if it were the graph would be angled up starting at the origin).

For the second question, my reasoning for picking C is that by varying the resistance of the variable resistor, you can decide how much current to split into each branch

That would be great if the power source were a current source but it isn't. It's a voltage source and the variable resistor in C has NO effect at all on the current that goes through the lamp.

And by the way, please don't shout (using all bold is shouting)

 

[CWatters]

D is wrong because below V0 there is a voltage but no current. So the resistance is infinite not zero.