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Electromagnetic Induction
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Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Dec 28, 2015

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Page 1: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Electromagnetic Induction

Page 2: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

J.J. Thomson was the first to measure the charge-to-mass ration of electron

Page 3: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.
Page 4: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Mass SpectrometersMass spectrometry is an analytical technique that identifies the

chemical composition of a compound or sample based on the q/m of charged particles.

Page 5: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Area 1 of Mass Mass Spectrometers – The Velocity

Selector

• The sample need to travel STRAIGHT through the plates. The electric field and the magnetic field will apply a force in such a way as to CANCEL out the electric force caused by the electric field.

Page 6: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Example problem

• Protons passing without deflection through a magnetic filed of 0.60 T are balanced by a ( 4.5x103 N/C) electric field. What is the speed of the moving protons?

• Known variables: • B = 0.60 T • E = 4.5x103 N/C• v = ?

Page 7: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Protons passing without deflection through a magnetic filed of 0.60 T are balanced by a ( 4.5x103 N/C) electric field. What is the speed of the moving protons?

• Bqv = Eq

• v = Eq / Bq

• v = E/B • (4.5x103 N /C) / (0.60 T) = 7.5x103 m/s

Page 8: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

M.S. – Area 2 – Detector Region

• After leaving region 1 in a straight line, it enters region 2, which ONLY has a magnetic field. This field causes the ion to move in a circle separating the ions separate by mass. This is also where the charge to mass ratio can then by calculated.

Page 9: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Electromagnetic Induction

• Wind pushes the blades of the turbine, spinning a shaft attached to magnets. The magnets spin around a conductive coil, inducing an electric current in the coil, and eventually feeding the electrical grid.

Page 10: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Can magnetic fields cause currents?

• we know that a current creates a magnetic field

• Can magnetic fields cause currents?

• Michael Faraday (1791–1862) and the American scientist Joseph Henry (1797–1878) independently demonstrated that magnetic fields can produce currents

Page 11: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Creating current-electromagnetic induction

• 2 ways to generate current –

• 1- conductor can move through a magnetic field

• 2- magnetic field can move past conductor

• Relative motion between between the wire and the magnetic field will produce the current (I).

Page 12: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

The galvanometer is used to detect any current induced in the coil on the bottom

No current flows through the galvanometer when the switch remains closed or open

Current is Only detected during the instance when the switch is being closed or opened.

Page 13: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Electromotive Force – (NOT A FORCE)

• EMF - When a voltage is generated by a battery, or by the magnetic force according to Faraday's Law, this generated voltage has been traditionally called an "electromotive force” emf

• Note : Emf is not a force.

• .

Page 14: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

EMF

• It is potential difference and is measured in volts (V ).

Page 15: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Moving a wire through a magnetic field

• A force is exerted on the charges

• Charges move in the direction of the force

• Work is then done on the charges

• (EPE) and electric potential(V) is increased

• The difference in potential(V) is called induced EMF

• EMF - measured in volts

• Depends on magnetic field B

• The length of the wire in the magnetic field L

• Velocity- v of the wire in the field

• EMF = BLv

Page 16: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.
Page 17: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Practice problem

• A strait wire .05m long, is moved straight up at a speed of 20 m/s through a 0.4 T magnetic field pointed in the horizontal direction.

• What is the EMF induced in the wire?

• The wire is part of a circuit of total resistance of 6.0Ω. What is the current in the circuit?

Page 18: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

A strait wire .05m long, is moved straight up at a speed of 20 m/s through a 0.4 T magnetic field pointed in the horizontal

direction.

• Known:• B magnetic field = (0.4 T)

• L wire length = (0.4 T)

• v speed of wire = (20.0m/s)

• R resistance = 6.0Ω

• EMF (V) = ?• Current (I) = ?

• EMF = B L v

= (0.4 T) (0.05m) (20.0m/s)

=.4 V

I = V/R

= .4V/ 6.0Ω =.067A

Page 19: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

magnetic flux, =BA

• Magnetic flux F is defined by F=BA

• B is the magnetic field

• A is the area perpendicular to the magnetic field

• Any change in magnetic flux (BA) induces an emf

Page 20: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

• emf is directly proportional to the change in flux

• emf is greatest when the change in time• Δt is smallest—that is, emf is inversely

proportional to Δt

• coil has N turns, an emf will be produced that is N times greater than for a single coil, so that emf is directly proportional to N

• EMF = −N (ΔBA/ Δt)

Page 21: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

• EMF = −N (ΔBA/ Δt)

Page 22: Electromagnetic Induction. J.J. Thomson was the first to measure the charge-to-mass ration of electron.

Variations of Faraday's Law