Question 2
In activity 19.5, the 5 Ω resistor is replaced by the 20 Ω one. What happens to the bulb?
The right answer is the one marked above.
The bulb gets dimmer. More resistance means less current, and the bulb’s brightness depends on the current through it.
Watching the bulb is a way of watching the current without reading a meter — which is the point of doing the activity with a bulb rather than an ammeter.