CIE iGCSE Co-ordinated Sciences-P4.5.3 Magnetic effect of current- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P4.5.3 Magnetic effect of current – Study Notes
CIE iGCSE Co-ordinated Sciences-P4.5.3 Magnetic effect of current – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Supplement
- Describe the pattern and direction of the magnetic field due to currents in straight wires and in solenoids
- Describe the effect on the magnetic field around straight wires and solenoids of changing the magnitude and direction of the current
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Magnetic Field Due to Currents
When an electric current flows through a conductor, it produces a magnetic field around it. The pattern and direction depend on whether the conductor is a straight wire or a solenoid.
1. Straight Wire
- The magnetic field lines form concentric circles around the wire.
- The direction of the field is given by the Right-Hand Grip Rule (thumb in the direction of current, fingers curl in the direction of the field lines).
- The field is strongest near the wire and gets weaker further away.
2. Solenoid (Coil of Wire)
- A solenoid is a long coil of wire with many turns.
- The magnetic field inside is strong and almost uniform (parallel field lines).
- The pattern is similar to that of a bar magnet with a clear North and South pole.
- The direction of the field is again given by the Right-Hand Grip Rule (fingers curl in the direction of current through the coil, thumb points towards the North pole).
Key Features:
- Straight wire: Circular field lines around the wire.
- Solenoid: Strong, uniform field inside, bar-magnet-like field outside.
- Field strength increases with:
- Higher current.
- More turns of the coil (solenoid).
- Adding a soft iron core inside the solenoid.
Summary Table
| Conductor | Magnetic Field Pattern | Direction Rule |
|---|---|---|
| Straight Wire | Concentric circles around the wire | Right-Hand Grip Rule (thumb = current, fingers = field) |
| Solenoid | Similar to bar magnet, uniform inside coil | Right-Hand Grip Rule (fingers = current, thumb = N pole) |
Example :
If the current in a vertical straight wire flows upwards, what is the direction of the magnetic field around it?
▶️ Answer/Explanation
Step 1: Use the Right-Hand Grip Rule: thumb = current (upwards).
Step 2: Fingers curl around the wire → field circles anticlockwise when viewed from above.
Final Answer: The magnetic field around the wire is anticlockwise when viewed from above.
Effect of Changing Current on Magnetic Fields
1. Straight Wire
- Magnitude of Current: Increasing the current makes the magnetic field stronger (field lines closer together). Decreasing the current weakens the field.
- Direction of Current: Reversing the current reverses the direction of the field lines (use Right-Hand Grip Rule).
- Example: If current flows upwards, the field circles anticlockwise (viewed from above). If reversed downwards, the field circles clockwise.
2. Solenoid
- Magnitude of Current: Increasing the current increases the field strength inside and outside the solenoid (similar to making the “bar magnet” stronger). Adding more current produces a stronger magnetic effect.
- Direction of Current: Reversing the current reverses the poles of the solenoid (North becomes South and vice versa).
- Example: If current flows so that, using the Right-Hand Grip Rule, the thumb points to the left, the left end is North. Reversing current makes the right end North.
Key Points:
- Magnetic field strength is proportional to the current in the wire/solenoid.
- Reversing current → reverses magnetic field direction.
- Adding a soft iron core inside a solenoid also increases field strength, independent of current direction.
Summary Table
| Conductor | Increase Current | Reverse Current |
|---|---|---|
| Straight Wire | Stronger circular magnetic field | Reverses circular field direction |
| Solenoid | Stronger uniform field (like stronger bar magnet) | Reverses solenoid poles (North ↔ South) |
Example :
If the current in a solenoid is doubled, what happens to its magnetic field strength? What happens if the current is then reversed?
▶️ Answer/Explanation
Step 1: Doubling the current doubles the magnetic field strength (more flux lines).
Step 2: Reversing the current reverses the polarity of the solenoid (North ↔ South).
Final Answer: The solenoid’s field becomes stronger with increased current, and its poles reverse when the current is reversed.