Magnetic Effects of Current & Magnetism
(Physics – INSPIRE Scholarship – Beginner Notes)
1. What We’ll Learn
- How electric current makes a magnet.
- How magnets push or pull on moving charges.
- How everyday magnets work inside our homes.
- A quick way to remember the direction of forces (Right‑Hand Rule).
2. Quick Glossary (No Jargon, Just Words)
| Word | Everyday Analogy | Short Meaning |
|---|---|---|
| Current | Water flowing through a hose | Flow of electric charge (how many electrons move per second) |
| Magnetic Field | Invisible wind around a magnet | The space where magnetic forces can act |
| Magnet | A fridge magnet | A material that can attract iron or other magnets |
| Force | Push or pull on a toy car | The action that changes motion |
3. Why Does a Wire Become a Magnet?
- Oersted’s Experiment – In 1811, Hans Oersted pulled a compass needle near a current‑carrying wire.
The needle moved! - Why?
- Moving charges (electric current) create a magnetic field around the wire.
- The field lines go around the wire in circles, like a whirlpool around a drain.
Everyday picture: Think of a spinning top. The top’s spin creates a swirling air pattern around it. A steady electric current creates a swirling magnetic field.
4. Drawing the Field Lines
- For a straight wire, the lines form concentric circles around it.
- The direction of the field depends on the direction of the current.
- Right‑Hand Rule – Point your thumb in the direction of the current. Your fingers curl in the direction of the field lines.
Tip: Hold a wire in your right hand, thumb = current, fingers = field.
5. Force on a Moving Charge (The “Magnetic Push”)
- A charge moving in a magnetic field feels a sideways push.
- The push is perpendicular to both the charge’s motion and the magnetic field.
Simple Equation (no heavy math!)
Force = (charge) × (velocity) × (magnetic field)
- Bigger charge, faster speed, or stronger field → stronger push.
Real life: In a mobile phone, the tiny magnets in the speaker push the coil to make sound.
6. Magnet‑On‑Magnet Forces
- Magnets have north (N) and south (S) ends.
- Like ends (N‑N or S‑S) repel.
- Opposite ends (N‑S) attract.
Analogy: Two sticks of attraction‑and‑repulsion sticky tape. Stick the same sides together → they push apart. Opposite sides → they stick.
7. Types of Magnetic Materials
| Material | Magnetic Behaviour | Everyday Use |
|---|---|---|
| Ferromagnetic (e.g., iron) | Strong magnets, stay magnetised | Fridge magnets, speakers |
| Paramagnetic | Weakly attracted, lose magnetism when field removed | Some alloys, MRI machines |
| Diamagnetic | Repelled by magnets, very weak | Bismuth, some plastics |
8. Tiny Example Problem
Question
A 2‑ampere current flows through a straight wire that is 0.5 m long.
How strong is the magnetic field at a point 2 cm from the wire?
Quick Answer
Use the simple rule:
B (tesla) ≈ (μ₀ / 2π) × (I / r)
Where
- μ₀ ≈ 4π × 10⁻⁷ T·m/A (just a constant)
- I = 2 A
- r = 0.02 m
B ≈ (4π×10⁻⁷ / 2π) × (2 / 0.02)
B ≈ (2×10⁻⁷) × 100
B ≈ 2×10⁻⁵ tesla
Result: About 20 µT (micro‑teslas), a tiny field—just enough to sway a compass needle.
Remember: The closer you are to the wire, the stronger the field.
9. Quick Review Questions
- What happens to a compass needle near a current‑carrying wire?
- How does the Right‑Hand Rule help you find magnetic field direction?
- What does it mean for a magnet to attract or repel another magnet?
- Which type of material keeps its magnetism after the field is gone?
Try answering before looking at the answers below.
10. Answers
- It moves because the wire’s magnetic field pushes on the needle.
- Thumb = current; fingers = field direction around the wire.
- Like poles repel, opposite poles attract.
- Ferromagnetic materials (e.g., iron).
11. Take‑Away Take‑Home Message
- Electric current = tiny moving charges.
- Moving charges = invisible magnetic field (circles around the wire).
- Magnetic field = pushes on other moving charges or on magnets.
- Use the Right‑Hand Rule to keep track of directions.
Remember: Think of magnets and currents as invisible hands that can push or pull on each other, just like a gentle breeze can move a feather.
Happy studying!