For a filament lamp, the current is 0.50 A when the potential difference is 2.0 V, and 1.5 A when the potential difference is 12 V. What happens to the resistance of the lamp between these two readings?
It stays constant at 4.0 Ω4.0\ \Omega4.0 Ω, because the lamp is an ohmic conductor
It decreases from 8.0 Ω8.0\ \Omega8.0 Ω to 4.0 Ω4.0\ \Omega4.0 Ω as the potential difference rises
It increases from 1.0 Ω1.0\ \Omega1.0 Ω to 18 Ω18\ \Omega18 Ω as the potential difference rises
It increases from 4.0 Ω4.0\ \Omega4.0 Ω to 8.0 Ω8.0\ \Omega8.0 Ω as the potential difference rises