Magnetic Force and Separation Distance

This experiment measures the force between two permanent bar magnets as their separation distance changes. Students collect data and plot graphs to investigate the mathematical relationship, which approximates an inverse square law but may follow a slightly different power law.

1. Set up two bar magnets so that their poles face each other at varying distances.
2. Use a force sensor, spring balance, or similar method to measure the magnetic force at each separation distance.
3. Record force readings at several different distances.
4. Plot force versus distance on standard graph paper to see the relationship.
5. Re-plot data using logarithmic scales (log(force) vs. log(distance)) to identify whether the data follows an inverse square law or another power relationship.
6. Determine the slope of the line from the log-log graph to find the exponent in the power law.

Magnetic force and separation distance #2 (NCPQ) - Dr Richard Walding:

• Try measuring repulsive forces (like poles facing) instead of attractive forces.
• Compare results with different types or sizes of magnets.
• Repeat with magnets aligned in different orientations (end-to-end vs. side-by-side).

• Handle strong magnets carefully to avoid pinching fingers.
• Keep magnets away from electronic devices, magnetic storage, and credit cards.
• Avoid dropping magnets, as they may chip or shatter.

• What relationship exists between force and separation distance? (It follows a power law, close to an inverse square.)
• Why does the log-log graph give a straight line? (Because a power law appears linear when both variables are plotted on logarithmic scales.)
• How does this compare to gravitational or electrostatic forces? (They both follow an exact inverse square law, F ∝ 1/r².)
• What might cause deviations from the exact inverse square law in this experiment? (Magnet imperfections, finite magnet size, alignment issues, or measurement errors.)