IB MYP 4-5 Physics- Magnetic effect of a current - Study Notes - New Syllabus
IB MYP 4-5 Physics-Magnetic effect of a current – Study Notes
Key Concepts
- Magnetic effect of a current
Magnetic Effect of a Current
Magnetic Effect of a Current
The magnetic effect of electric current was discovered by Hans Christian Ørsted in 1820.
- He found that a current-carrying wire deflects a nearby compass needle → showing that an electric current produces a magnetic field.
- This phenomenon is also called the electromagnetic effect.
Basic Idea
- Whenever an electric current flows through a conductor (like a wire), it produces a magnetic field around it.
- The strength of this magnetic field depends on:
- The magnitude of the current (larger current → stronger field).
- The distance from the wire (closer → stronger field).
- The shape of the conductor (straight wire, loop, coil, solenoid).
Direction of the Magnetic Field
Given by the Right-Hand Grip Rule (or Right-Hand Thumb Rule):
- Thumb → points in the direction of current.
- Curled fingers → show the direction of magnetic field lines around the wire.
Magnetic Fields due to Different Conductors
Straight Wire:
Produces circular magnetic field lines around it.
Circular Loop:
Field lines combine at the center, making the field stronger.
Solenoid (coil of many loops):
Produces a field similar to a bar magnet → one end acts as north, the other as south.
Electromagnet:
A solenoid wrapped around a soft iron core, creating a strong and controllable magnetic field.
Applications
- Electromagnets (cranes, relays, door locks).
- Electric motors (convert electrical → mechanical energy).
- Generators (convert mechanical → electrical energy).
- Loudspeakers and microphones.
Example:
A current flows horizontally from left to right through a straight wire. What is the direction of the magnetic field above and below the wire?
▶️ Answer/Explanation
Step 1: Apply the Right-Hand Grip Rule → thumb points to the right (current direction).
Step 2: Fingers curl around the wire showing circular magnetic field lines.
Step 3: Above the wire → field points into the page (✗). Below the wire → field points out of the page (•).
Final Answer: Above → into page, Below → out of page.
Example:
A circular loop carries current in the anticlockwise direction when viewed from above. What is the direction of the magnetic field at the center of the loop?
▶️ Answer/Explanation
Step 1: For each segment of wire, apply Right-Hand Grip Rule.
Step 2: At the center, all field contributions add together.
Step 3: For anticlockwise current → field points out of the page.
Final Answer: Magnetic field at the center points out of the page.
Example:
How does the magnetic field inside a solenoid carrying current compare with that of a bar magnet?
▶️ Answer/Explanation
Step 1: Inside the solenoid → field lines are straight, parallel, and equally spaced → uniform strong field.
Step 2: One end behaves as a north pole, the other as a south pole.
Step 3: Outside, field lines curve from N to S, similar to a bar magnet.
Final Answer: A solenoid with current produces a bar-magnet-like field with uniform strength inside.