Magnetic Fields

Grade 12 · Physics

Semester 1 | Period 3 | Week 14

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Subject: Physics

Semester: 1

Period: 3

Week: 14

School Name:

Teacher’s Name:

Subject: Physics

Grade Level: Grade 12

Week & Period: Week 14, Period III

Date:

Topic: Magnetic Fields
Sub-Topic: Types, Magnetic Flux, Magnetic Flux Density, and Force in a Magnetic Field

Learning Objectives:

By the end of the lesson, learners should be able to:

  1. Define magnetic fields and explain how they are represented.
  2. Differentiate between uniform and non-uniform magnetic fields.
  3. Define magnetic flux and flux density and relate them mathematically.
  4. Analyze the force experienced by a current-carrying conductor in a magnetic field.
  5. Apply Fleming’s left-hand rule.

 

Instructional Materials:

  • Bar magnets
  • Iron filings
  • Cardboard sheet
  • Compass
  • Current-carrying conductor (wire)
  • Power source
  • Galvanometer
  • Permanent magnets
  • Magnetic field demonstrator

 

Anticipation (Warm-Up Activity):

Pose the question:

“Why does a compass needle always point in a particular direction?”
Demonstrate the deflection of a compass in the presence of a bar magnet.

 

Building Knowledge (Main Lesson):

  1. Magnetic Field:
  • Defined as the region around a magnet where magnetic forces are experienced.
  • Represented by lines of force or field lines.
  • The direction of the field is from the North to the South pole.
  1. Types of Magnetic Fields:
  • Uniform Field: Field lines are parallel and equally spaced (e.g., between two opposite poles of magnets).
  • Non-Uniform Field: Field lines are curved and not equally spaced (e.g., around a single bar magnet).

    

  1. Force in a Magnetic Field:
  • When a current-carrying conductor is placed in a magnetic field, it experiences a force.
  • The direction is given by Fleming’s Left-Hand Rule:
    • Thumb = Force
    • First Finger = Magnetic Field
    • Second Finger = Current
  • Magnitude of Force (F):

Where:
F = Force (N),
B = Magnetic Flux Density (T),
I = Current (A),
L = Length of conductor in the field (m),
θ = Angle between conductor and field

 

Activities/Experiment:

Experiment 1: Observing Magnetic Field Patterns

Materials: Bar magnet, iron filings, cardboard
Procedure:

  • Place the magnet under the cardboard.
  • Sprinkle iron filings evenly.
  • Tap gently.
    Observation:
  • Filings arrange along curved lines from N to S pole.
    Conclusion:
  • Magnetic field lines emerge from the North pole and return to the South pole.

 

Experiment 2: Magnetic Field Due to Current

Materials: Straight wire, compass, power source
Procedure:

  • Connect wire to battery
  • Place compass around wire and observe deflection
    Conclusion:
  • A current in a wire produces a circular magnetic field around the wire

 

Sample Calculation:

Question:
A straight conductor of length 0.5 m carrying a current of 4 A is placed perpendicular to a magnetic field of flux density 0.2 T. Calculate the force on the conductor.

 

Assessment (Class Work):

  1. Define magnetic flux and flux density.
  2. Differentiate between uniform and non-uniform magnetic fields.
  3. State and explain Fleming’s Left-Hand Rule.
  4. A wire of length 0.8 m carrying 5 A current lies in a magnetic field of 0.5 T. Calculate the force on the wire if it makes an angle of 30° with the field.
  5. Sketch the magnetic field around a bar magnet.

 

Homework:

  • Research and write two real-life applications of magnetic force.
  • Use Fleming’s left-hand rule to determine the direction of motion in electric motors.

 

Expanded Notes:

  • Magnetic flux density is strongest where the field lines are closest.
  • Electric motors use magnetic force to convert electrical energy into motion.
  • Loudspeakers use the force on a coil in a magnetic field to vibrate a diaphragm.

 

Differentiation:

  • Use 3D models for field line representation.
  • Engage students with simulation apps for magnetic force and fields.
  • Group learners to measure and draw magnetic field patterns.

 

Teacher’s Reflection:

  • Were learners able to differentiate field types visually and conceptually?
  • Did they apply the force formula and rule correctly in calculations and predictions?
  • How well did hands-on experiments reinforce abstract concepts?