1. Right-Hand Rule (Straight Wire)

"Thumb UP, fingers CURL"

• Point right thumb along current direction → curled fingers = B field direction
• For current going up: B circles counter-clockwise when viewed from above

2. Right-Hand Rule (Force on Charge — FBI Rule)

"F = B × I" or use three fingers:

• Index → B (field direction)
• Middle → I (current / velocity of positive charge)
• Thumb → F (force direction)
• For negative charge: reverse the thumb direction

3. DPF Rule for Magnetic Materials

"Dia Pushes Far, Para Pulls Weakly, Ferro Flies In"

• Diamagnetic → Pushed out (repelled), moves to weaker field region
• Paramagnetic → Pulled in weakly (weakly attracted)
• Ferromagnetic → Flies into the field (strongly attracted)
• Extra: "Diamond is Dia; Aluminium is pAra; Iron is ferro"

4. Ammeter vs Voltmeter

"A-Low, V-High" (AV pattern)

• Ammeter = Low resistance = parallel Shunt = Small S
• Voltmeter = High resistance = Series R = huge R
• Memory: "Ammeter is like a bridge (parallel path); Voltmeter is like a wall (in the way)"

5. Solenoid vs Toroid

"Solenoid is Straight, Toroid is a Tyre"

• Solenoid: straight cylinder, uniform B inside, zero outside
• Toroid: donut shape, B = μ_{0}NI/(2πr) inside ring, zero in hole AND outside

6. Key Numbers to Remember

• μ_{0} = 4π × 10^{-7} T·m/A ≈ "4π nano" (nano = 10^{-7} is approximate)
• 1 T = 1 N/(A·m) = 1 kg/(A·$s^{2}$)
• e = $1.6 \times 10^{-19}$ C; m_p = $1.67 \times 10^{-27}$ kg; m_e = $9.1 \times 10^{-31}$ kg

7. Hysteresis Loop Points

"Retentivity = Remembered; Coercivity = Cancelled"

• Retentivity = B when H = 0 (material retains magnetism)
• Coercivity = −H when B = 0 (field needed to coerce magnetism to zero)