I have a physics mid year exam tomorrow and I'm already so late with my studies AND it's 10:30pm should I study each chapter or just start answering questions and correcting?

Explain why electric current cannot exist if a current doesn't have a voltage source.

Consider a 1000 w iron whose base plate is made of 0.5 cm thick aluminum alloy 2024-t6 (ρ = 2770 kg/m3 and cp = 875 j/kg°c). the base plate has a surface area of 0.03 m2. initially, the iron is in thermal equilibrium with the ambient air at 22°c. assuming 90% of the heat generated in the resistance wires is transferred to the plate, determine the minimum time needed for the plate temperature to reach 200°c.

What are the similarities & differences between a thermistor and a light dependent resistor in physics?