Question 1
In activity 19.3 the switch is closed, the readings taken as quickly as possible, and the switch opened again. Why?
The right answer is the one marked above.
To stop the nichrome coil heating up. The coil’s temperature rises while a current passes through it, and the activity has to be done with the temperature kept constant.
This is not a detail of technique. The constant ratio only appears at constant temperature, so the condition is part of the law itself.