AQA ยท A level Physics

Battery pressure and internal resistance A-level challenge

Can you get 100%? Use research into clamped lithium-ion cells to test stress, internal resistance and terminal potential difference in one original A-level Physics question.

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Question

8 marks

Show your working and give units where appropriate.

1(a)

AQA defines tensile stress as force divided by cross-sectional area. Engineers use the same force-per-area relationship to quote the mean compressive stack pressure on a pouch cell. A flat lithium-ion cell has face area 1.20 x 10^-2 m^2. A test rig applies a uniform compressive force of 480 N perpendicular to the face. Calculate the mean stack pressure.

[2 marks]

1(b)

The cell has emf 4.00 V and supplies a current of 8.0 A. Its internal resistance is initially 0.040 ohm. Calculate the terminal potential difference of the cell.

[3 marks]

1(c)

Excessive stack pressure can reduce open pathways for lithium ions and increase the cell's internal resistance. The current remains 8.0 A while the internal resistance rises to 0.100 ohm. Calculate the new terminal potential difference and explain why a larger internal resistance can increase unwanted heating inside the cell.

[3 marks]

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