No problem! For 2b, as its three marks I’m not too sure where each point is coming from but this is my best guess:
•Power dissipated is energy lost per second
•This energy is lost (dissipated) as thermal energy in the wire.
•The fixed resistor reduces the potential difference across the wire, therefore reducing the current in the wire.
•This means that the resistance is reduced in the wire, thus reducing the thermal energy emitted.
•Overall reducing power dissipated in the wire.
Now that’s probably over kill but I write all my answers in bullet points (even in the exam) so I can logically sort through my response
For the last bit: you aren’t given any length. It says a larger diameter but doesn’t give a value, so all we know is the cross-sectional area is greater than before. There’s more room in the wire meaning the electron collisions are less frequent, which reduces the resistance.
So with that in mind I’d draw an identical line (same gradient) just underneath the line on the graph.
I hope that helps!