GCSE PHYSICS - MAGNETISM AND ELECTROMAG - LESSON 9 - magnetic field of current carrying wire

Magnetic Field Produced by a Current-Carrying Wire

Introduction to Magnetic Fields

• The lesson focuses on the magnetic field generated by a wire carrying an electric current. The scenario involves visualizing the wire passing through a sheet of paper as the current flows.

Characteristics of the Magnetic Field

• The magnetic field around the wire forms concentric circles, with the wire at their center. This pattern is crucial for understanding how magnetic fields behave around conductors.

• As the intensity of the current increases, so does the strength of the magnetic field, indicating that they are directly proportional to each other.

Direction of Magnetic Field

• The direction of current flow is from positive to negative; in this case, it flows downwards through the paper. Understanding this direction helps determine how to visualize and remember magnetic field orientation.

• A practical analogy using a screwdriver illustrates that turning it clockwise (to screw into wood or paper) corresponds to a clockwise magnetic field when current flows downwards. Thus, arrows can be drawn in this direction for clarity.

Reversing Current Direction

• When reversing the battery connections, causing current to flow upwards through the paper, one must turn the screwdriver anti-clockwise to unscrew it out of wood/paper—indicating an anti-clockwise magnetic field direction in this scenario.

Notation for Current Direction

• Important notation is introduced:

• Current flowing into paper is represented like a dart going away from you (tails visible).

• Conversely, if current comes out towards you, it's depicted as seeing its point coming towards you.

• These notations help clarify whether currents are entering or exiting relative to your viewpoint and their corresponding magnetic fields (clockwise vs anti-clockwise).

Conclusion and Future Topics