We can model the rear window defroster in a car as a resistor that is connected to the car's 12 V battery. The defroster is made of a material whose resistance increases rapidly as the temperature increases. When the defroster is cold, its resistance is low; when the defroster is warm, its resistance is high. Why is it better to make a defroster with a material like this than with a material whose resistance is independent of temperature? Think about how the resistance, the current, and the power will change as the window warms.