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Transformers
Key circuit element that changes voltage from a main source and distributes power. Voltage is changed without changing frequency of the ac power source. It is a system with a primary coil (labeled P) and a secondary coil (labeled S) wound around a soft iron core.
Transformer equation: relationship between primary (input), VP, and secondary (output), VS, voltages
S S P P
V N
V N
(turns ratio);
I
I
S P P S
N
N
[power conserved]
Step –up Transformer: VS greater than VP [NS > N (^) P ]
Step –down Transformer: V (^) P greater than VS [NP > NS ]
Seismograph:
Maxwell’s Equations (1865)
- Electric fields result from electric charges (Coulomb’s Law)
- Magnetic fields are continuous (no magnetic charges or monopoles)
- Changing magnetic field produces an electric field (Faraday’s Law of Induction)
- Magnetic field is produced by an electric current (Oersted, Ampere), or by a changing electric field (Maxwell’s hypothesis)
Electromagnetic Waves (EM Wave)
- No medium required for EM waves
- Transverse waves that consist of oscillating electric and magnetic fields, which are perpendicular to each other and to the direction of propagation
- Electric and magnetic fields are in phase
Light is an electromagnetic wave with velocity c,
where c. x m/s o o
(free space
value)
E cB
Measuring the speed of light
Angular separation between consecutive 450 notches
∆θ=(1/450) rev ∆t= ∆θ/ω=(1/450) rev/[35 rev/s]
∆t=6.4x10-5^ s
c=2d/ ∆t=(19000 m/ 6.4x10 -5^ s) = 3.0x10 8 m/s
Electromagnetic spectrum
EM waves with different frequencies (f), and wavelengths (), but same velocity (c).
Production of Electromagnetic Waves
EM Waves produced by accelerating electric charges
- Charges accelerating in a straight line produce EM waves in directions perpendicular to acceleration (donut shaped around charge)
- Circling charges (synchrotron radiation)-emit cones of EM waves (visible and x-rays).
- Oscillating charges and currents-dipole radiation-radio waves
- Atomic EM waves-will discuss later
