#### 11.2.1 Describe the production of an induced e.m.f by relative motion between a conductor and a magnetic field (motionally induced e.m.f.).

When a conductor is moved through a magnetic field an electric current is induced in the conductor. Which makes sense, before we discussed how a moving electric charge feels a force due to a magnetic field, by moving the conductor we are moving the charges… Faraday found that the strength of the induced e.m.f. was proportional to:

- The speed of the movement
- The strength of the magnetic field
- The number of turns on the coil
- The area of the coil.

#### 11.2.2 Derive the formula for the e.m.f. induced in a straight conductor moving in a magnetic field

The force on the electrons in wire due to a magnetic field is:

(1)Thus we can say the potential difference (induced e.m.f. ) between the two ends of a conductor of length l is equal is defined as:

(2)If the angle between the conductor and the magnetic field is 90° then the formula simplifies to:

(4)*This last equation is in your IB formula handbook.*

#### 11.2.3 Define magnetic flux and flux linkage.

#### 11.2.4 Describe the production of an induced e.m.f. that is produced by a time-changing magnetic flux

#### 11.2.5 State Faraday’s law.

#### 11.2.6 Explain how a motionally induced e.m.f. can be equated to a rate of change of magnetic flux.

Magnetic flux is defined at the magnetic field strength times the area swept out by a conductor. Or in simpler terms it can be thought of as the number of magnetic field lines (which don’t really exist…) passing through a region. Mathematically we define magnetic flux as:

(5)Where A is the area swept out, B is the magnetic field strength and θ is the angle between the direction of motion and the magnetic field lines. The unit of magnetic flux is the Weber, Wb.

The area swept out by a moving straight conductor (a wire) is:

(6)Where *l* is the length of the wire and $\Delta x$is the distance the wire moves, substituting into the magnetic flux equation:

Therefore the change in magnetic flux per time is equal to, assuming the angle is zero:

(8)Which we can recognize from above as the induced e.m.f.

(9)This last equation is called Faraday’s law.

The flux linkage is defined as the number of loops (N) multiplied by the induced e.m.f. If there is N number of wires passing through the magnetic field then we can write the induced e.m.f. as:

*This last equation is in your IB formula handbook.*

#### 11.2.7 State Lenz’s law.

The emf induced in an electric circuit always acts in such a direction that the current it drives around the circuit opposes the change in magnetic flux which produces the emf.

If you move a conductor through a magnetic field a small current will be generated. The current will create a magnetic field, the current will always be in the direction so as to generate a force in the opposite direction as the motion. Almost like inertia.

thank you so much for your effort in trying to make the public understand the nature of physics.i have read the notes and i do appreciate sincerely.however,it would have served very well i you had included the calculation part of it.in addition,areas of the applicability of the topic and how the study of such a topic would help people change their attitude towards physics which many view as very difficult and impossible to do.keep up please.thank you.

ReplyOptionsis the equation explained above is for condutor moving parallel to plan? actully i want emf equation for conductor moving in magnetic field in circular direction when one end of he condutor is hinged i.e conductor will be moving in 360 degree… please can u help me..

ReplyOptionsWhat happens when a straight conductor is moving through a magnetic field whose strength is not the same throught all the points in the motion?

ReplyOptionsThe the force on the conductor would not be constant. If the magnetic field can be described by a function then the "B" in the equation(s) would be substituted with the function.

ReplyOptionsIts based on the fleaming's left hand rule.

ReplyOptionsIs it me or is this based on the old syllabus

ReplyOptionsYep. It is. I haven't taught IB Physics in several years. Use what you can…

ReplyOptionsGod bless all of you.

ReplyOptionsIt is important to add an explanation for the variation in flux due to the variation of the angle between the normal and the field.

ReplyOptionsFUck you

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