Lecture 23

# Lecture 23 - Quiz 4 Is Friday 4:30-5:45 in CW101,102,103...

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Quiz 4 • Is Friday, 4:30-5:45 in CW101,102,103. • Covers Faraday’s Law, inductance, AC circuits, oscillators, sound and EM waves. • Review: tonight, 7:30PM, CW102. • SAS Review, tomorrow, 6:00PM, Fiedler Auditorium.

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Electromagnetic Waves • First of all, let’s just assert that EM waves exist. We’ll connect them to E and B fields later. • What is the elastic medium (the string or the fluid)? Nothing! EM waves travel through empty space. • We know their speed: v P =c=3×10 8 m/s. Note that this is 10 6 ×v P for sound. • If these are EM waves, then their speed should follow from EM properties of free space, ε 0 and µ 0 . • Dimensional analysis then implies c=(1/ ε 0 µ 0 ) 1/2 . Plugging in the numbers, it works!
λ ,f, I for EM waves We perceive f for sound wave as pitch. What do we perceive f for light waves? A. Color. B. Brightness. C. Opacity. D. Shininess.

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λ ,f, I for EM waves We perceive I for sound wave as volume. What do we perceive I for light waves? A. Color. B. Brightness. C. Opacity. D. Shininess.
• Electromagnetic waves exist for all frequencies, as far as we know. We refer to light as the f, λ range that are eyes are sensitive to. • The range is approximately 380 nm< λ < 760 nm, about one “optical octave”, not as good as our ears. • However, like the ears, our eyes have a dynamic range of 100 dB.

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How you see, rods and cones • In essence, the eye consists of an adjustable aperature to let light in (the pupil), a lens system to focus the light (later…), and a receptor system (the
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## This note was uploaded on 05/11/2010 for the course ＰＨＹ 214 taught by Professor Timothybolton during the Spring '10 term at Kansas State University.

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Lecture 23 - Quiz 4 Is Friday 4:30-5:45 in CW101,102,103...

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