To determine how to best visualize the difference in magnetic field patterns produced by a straight current-carrying wire and a current-carrying circular loop, we need to understand the nature of each magnetic field:

1. Magnetic Field of a Straight Current-Carrying Wire: The magnetic field around a long, straight wire carrying a current is circular, with field lines forming concentric circles centered on the wire. The direction follows the right-hand grip rule – if the thumb of the right hand points in the direction of the current, the fingers curl in the direction of the field lines.
2. Magnetic Field of a Current-Carrying Circular Loop: The magnetic field produced by a circular loop carrying current has a more complex pattern. The field lines are denser towards the center of the loop and form a closed loop structure. Within the loop, the lines are almost straight and parallel to each other, and outside, they resemble that of a bar magnet.
3. Experimental Setup: To visualize the magnetic field lines, using iron filings is highly effective. Sprinkling iron filings around both the straight wire and the circular loop will reveal the pattern of magnetic fields by aligning along the field lines due to the magnetic force exerted on them.

Considering the options, the correct experimental setup is:

Correct Answer: Using iron filings around both the straight wire and the circular loop to visualize their magnetic field patterns.

Explanation:

1. Option 1: Using a compass near the wire only detects the field direction at specific points, not the overall pattern.
2. Option 2: The force between parallel wires does not illustrate magnetic field patterns; it relates to magnetic forces and attractions.
3. Option 3: Iron filings successfully visualize field patterns for both a straight wire and a circular loop, contrasting their shapes and densities.
4. Option 4: Using a bar magnet near the configurations doesn't show field patterns effectively, focusing rather on forces of attraction or repulsion.

This method, using iron filings, provides a clear understanding and visual illustration of the differences in magnetic field patterns generated by the two types of conductors, which is vital for understanding concepts in electromagnetism.