Final answer:
Legally, headlights must be turned on from dusk until dawn. In the scenario provided, a car with a 100 Ah 12-V battery and two 40 W headlights would have the headlights last for approximately 15 hours before the battery drains.
Step-by-step explanation:
By law, your vehicle's headlights must be turned on from dusk until dawn to ensure visibility and safety on the roads. Headlights help drivers see and be seen by others, especially during times when natural light is low. In specific scenarios like fog, heavy rain, or snow, headlights should also be used regardless of the time of day.
In reference to the given scenario, let's estimate how long the headlights in the car will remain on with the battery specs provided. The battery has a capacity of 100 Ah, which means it can supply 100 ampere-hours before running out. Since the headlights are rated at 40 W each and there are two of them, the total power consumption will be 80 W.
To find out how long the headlights will last, we first convert watts to amps using the formula I (current in amperes) = P (power in watts) / V (voltage in volts). So for each headlight: I = 40W / 12V = 3.33 A. For both headlights: 3.33 A * 2 = 6.66 A. The 12-V automobile battery rated at 100 Ah will last 100 Ah / 6.66 A = approximately 15 hours.