Theme D — Fields
D.4.1 Induced Emf — IB Physics HL Revision Notes & Topical Questions
5 min read 8 parts Lesson 35 of 39 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
D.4.1 Induced Emf — IB PHYSICS HL notes: Explain how an e.m.f. is induced when a conductor cuts magnetic field lines and use ε = BLv.Meaning — an e.m.f.
- Formal definition
- Force on electrons
- Charge separation
- Closed circuit
- Larger e.m.f
- Electromagnetic induction
Section 1 of 8Electromagnetic induction
Meaning
- Meaning an e.m.f. is induced due to relative movement between a conductor and a magnetic field
Ways
- Ways a conductor moves relative to the field or the field varies relative to a conductor
Formal definition
- Formal definition the process in which an e.m.f. or current is induced in a closed circuit due to changes in magnetic flux
Section 2 of 8How the e.m.f. arises
Force on electrons
- Force on electrons free electrons in a conductor that cuts field lines experience a magnetic force
Charge separation
- Charge separation work is done as charges move to the ends of the conductor
Energy
- Energy mechanical work is transferred to the charges as electric potential energy
Result
- Result a potential difference exists between the ends, which is the induced e.m.f.
Definition
- Definition induced e.m.f. is the work done per unit charge separating the charges to the ends of the conductor
Closed circuit
- Closed circuit an induced current can flow
Section 3 of 8Moving straight conductor
Condition
- Condition the conductor must be in a perpendicular field so it cuts the field lines
Circuit
- Circuit the rest of the circuit lies outside the field so the e.m.f. is induced across the conductor in the field only
Equation
- ε = BLv
Symbols
- ε in V, B in T, L the length in the field in m and v the speed in m s−1
Larger ε
- Larger ε longer conductor, stronger field or faster cutting of field lines
Coil
- ε = BLvN for N turns
Section 4 of 8Experiment 1: magnet and coil
1
Connect the coil to a sensitive voltmeter.
2
Hold the magnet still inside or outside the coil and the reading is zero because the flux does not change.
3
Move the magnet into the coil and a momentary reading appears as the flux changes.
4
Withdraw the magnet and the reading is in the opposite direction.
5
Move the magnet faster and the reading is larger because the rate of change of flux is greater.
- Larger e.m.f.
- faster movement, more turns on the coil or a stronger magnet
Section 5 of 8Experiment 2: wire between magnets
1
Connect a long wire to a voltmeter, with no current in the wire to begin with.
2
Hold the wire still and the reading is zero.
3
Move the wire between the magnets and an e.m.f. is induced as it cuts the field lines.
4
Move the wire out and the e.m.f. is in the opposite direction.
- Larger e.m.f.
- a longer wire, faster movement or stronger magnets
Section 6 of 8More from the specification
1Faraday's Law of Electromagnetic Induction
- Faraday's law states that induced electromotive force (voltage) in a circuit is directly proportional to the rate of change of magnetic flux linkage (ε = -N·ΔΦ/Δt),What the symbols mean: ε = induced e.m.f. (V) · N = number of turns · ΔΦ = change of flux (Wb) · Δt = time taken (s); the minus sign is Lenz’s law
- where magnetic flux Φ = B·A cos θ.
2AC Generation and Flux Angle
- In an alternating current generator, a coil rotating with angular frequency ω in a magnetic field of flux density B sweeps through angle θ = ωt;
- induced voltage reaches its maximum value when the plane of the coil is parallel to the magnetic field.
3Transformer Mutual Induction
- In a step-up or step-down transformer, an alternating voltage applied to the primary winding creates an alternating magnetic flux in the core that induces an alternating output emf across the secondary coil.
4Constant speed
- Speed that does not change.
5Electromagnetic induction
- Production of an e.m.f. by relative movement of a conductor and a magnetic field.
6Induction
- Charging an object without touching it, giving it the opposite sign to the charged object.
7Density
- Mass per unit volume.
8Frequency
- Revolutions per second, f = 1/T.What the symbols mean: T = period, the time for one complete wave (s) · f = frequency (Hz)
9Primary
- Input coil.
10Secondary
- Output coil.
11Angular speed
- Magnitude of the angular velocity.
12Mutual induction
- Induction of an e.m.f. in one circuit by a change of current in a neighbouring circuit.
13Alternating current
- Current that continually reverses direction.
14Φ = BA
What the symbols mean: Φ = magnetic flux (Wb) · B = magnetic flux density (T) · A = area at right angles to the field (m2)
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Electromagnetic induction | The induction of an e.m.f. or current in a closed circuit due to changes in magnetic flux. |
| Induced e.m.f. | The work done per unit charge in separating charges to the ends of a conductor. |
| ε = BLv | The e.m.f. induced in a conductor of length L moving at speed v perpendicular to a field B. |
| Flux cutting | The movement of a conductor across magnetic field lines. |
Section 8 of 8Exam technique
1
Saying an e.m.f. is induced in a stationary conductor in a steady field — the flux must change.
2
Putting the whole circuit in the field — only the moving conductor in the field gives the e.m.f.
3
Taking L as the whole wire length rather than the part inside the field.
4
Forgetting that reversing the motion reverses the induced e.m.f.
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