SME
Grade 11 Science · Physics
Magnetic fields, magnetic forces and electromagnetic induction
Use this for “The flux through a 50-turn coil changes by 0.012 Wb in 0.2 s. What emf is induced?” with Faraday’s law.
Diagram
emf = NΔΦ/Δt = 50 × 0.012/0.2 = 3 V
Pushing the N pole in, the coil’s current makes its near end an N pole that pushes back (Lenz’s law).
Faster motion or more turns: a bigger emf.
No motion: no current.
This is an example. Type your own values to start a new problem.
emf (V)
=
N
×
ΔΦ (Wb)
Δt (s)
Formulas
emf
=
N
×
ΔΦ/Δt
3 = 50 × 0.012/0.2
Assumptions
•
Only a changing magnetic flux through the coil induces an emf: a magnet held still makes none.
•
Faraday’s law: emf = NΔΦ/Δt, so more turns or a faster change give a bigger emf.
•
Lenz’s law: the current’s own field opposes the change, so pulling the magnet out swings the meter the other way.
Step-by-step
WE KNOW
N = 50, ΔΦ = 0.012 Wb, Δt = 0.2 s
FIND
induced emf (emf)
Step 1 · Find induced emf (emf)
Use emf = N × ΔΦ/Δt
Each
turn
gets
ΔΦ/Δt;
N
turns
add
up.
emf = 50 × 0.012/0.2
emf = 0.6/0.2
emf = 3 V
Check
Put the numbers back in. Both sides should match.
3 = 50 × 0.012/0.2 ✓
Topic check
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