Question

a rechargeable battery is connected to a portable electronic device. work is done on the device by the battery to keep it powered. as the battery discharges, the device becomes warm. which description best relates the sign for heat and work from the perspective of the battery? q=+,w=0 q=-,w=0 q=-,w=-

Explanation:

1. Understanding Sign Conventions for Thermodynamics (Battery as System):

• Work (w): The battery does work on the electronic device. From the system's (battery) perspective, when a system does work on the surroundings, the work is negative. So \( w = - \) (since the battery is expending energy to do work on the device).
• Heat (q): The device becomes warm, meaning heat is released from the battery to the device (surroundings). When a system releases heat to the surroundings, \( q \) is negative (by convention: \( q \) is positive when heat is absorbed by the system, negative when released). So \( q = - \).

1. Evaluating Options:

• First option (\( q=+, w=0 \)): Incorrect, as work is done by the battery (\( w

eq 0 \)) and heat is released (\( q \) should be negative).

• Second option (\( q=-, w=0 \)): Incorrect, as work is done by the battery (\( w

eq 0 \)).

• Third option (\( q=-, w=- \)): Correct, as the battery releases heat (\( q=- \)) and does work on the surroundings (\( w=- \)).

Answer:

q = -, w = -