Answer to Question #65352 in Electric Circuits for Helen

Question

When I arrived at Stevenson, my new employee gift bag from the School of the Sciences
included a cute LED flashlight. It is powered by a set of 3 AAA batteries so the LED
bulbs are supplied a potential difference of 4.50 V. If the batteries are rated to provide
a lifetime of about 1.20 Ah (ampere hours) and the LED bulbs have a net resistance
of 125 Ω, for how many hours can the LED flashlight operate? FYI, I gave it to my
son and he still uses it.

Answer 1

When I arrived at Stevenson, my new employee gift bag from the School of the Sciences
included a cute LED flashlight. It is powered by a set of 3 AAA batteries so the LED
bulbs are supplied a potential difference of 4.50 V. If the batteries are rated to provide
a lifetime of about 1.20 Ah (ampere hours) and the LED bulbs have a net resistance
of 125 Ω, for how many hours can the LED flashlight operate? FYI, I gave it to my
son and he still uses it.

Data: U=4.5V,Q=1.2Ah,R=125Ω;
Solution: I=U/R-current needed for LED functioning;Q=I*t_time of life=(U*t_time of life))/R;
t_time of life=(Q*R)/U=(1.2Ah*125Ω)/4.5V=33.3hours=1 d 9 h 20 m;