1. Phy2005 Applied Physics II Spring 2017 Announcements:
Test 2 Wednesday, March 22 Covers Ch
2 practice tests posted on course Tests page
Review session in class March 20 in class + March pm NPB 2205
+ March 21 5pm (Anne Tolson) NPB 2165

2. Last time E
EM wave B

3. Last time Intensity Solid angle W = A/R2 [steradian]
All electromagnetic waves such as light transmit energy.
Light intensity = power flowing through the area / area
(power density) [w/m2]
Solid angle A
W = A/R2 [steradian] W R
Total solid angle: W = 4pR2/R2 = 4p (sr)

4. 1 lumen (lm) = light power of 1/683 W in yellow (lighting industry)
When a light bulb is on, it radiates out broad spectrum
of EM wave. The total radiant energy emitted by the
lamp per unit time is called radiant flux.
Only a small portion of this is in visible range (400 –
700 nm). The portion of radiant energy in visible range
is called luminous flux (F).
In a incandescent light bulb, only 10% is luminous flux.
1 lumen (lm) = light power of 1/683 W in yellow (lighting industry)

5. Q. What solid angle is subtended at the center of 6 m diameter
sphere by a 2 m2 area on its surface?
W = A/R2
= (2 m2)/(3 m)2
= 0.22 sr R1 R2 W
Luminous intensity: I = F/W
(luminous flux per unit solid angle)
[lm/sr] = candela (cd)

6. Q. A spotlight is equipped with a 30 cd bulb. This light beams
onto a vertical wall in a circular shape with 3 m2 area. The spotlight
is 10 m from the wall. Calculate the luminous intensity for the
spotlight.
3 m2
10 m
Total luminous flux coming out of the bulb, F = I 4p
= (30 cd)(4p sr)
= 377 lm
This amount of luminous flux is concentrated on the 3 m2 spot.
To get the luminous intensity, we need to know the solid angle that
bright spot subtend.
W = A/R2
= (3 m2)/(10 m)2
= 0.03 sr
I (spot) = (377 lm)/(.03 sr) = 1.26 x 104 cd

7. Shadows

8. Eclipses

9. The eye

14. Q1 The intensity of the sun's radiation at the position of
the earth is 1340 W/m2. What is the total power
put out by the sun? The Earth-to-Sun distance is
1.5 x 1011 m.
I=1340 W/m2 = P/(4pR2)  P = (1340)(4p(1.5 x 1011 )2) =
3.8×1026 W

15. Clicker Quiz Time Log in your remote! ACADEMIC HONESTY
Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.
Log in your remote!

16. Q2 The intensity of the sun's radiation at the position of
the earth is 1340 W/m2. The Earth-to-Sun distance is
1.5 x 1011 m. What is the intensity of light falling on Saturn? The Saturn-to-Sun distance is 1.4 x 1012 m.
87 W/m2
15 W/m2
143 W/m2
87p W/m2
15/p W/m2 RE RS

17. Natural light is “unpolarized”.
Polarization of light E
Natural light is “unpolarized”.
We can produce polarized light from unpolarized light!!
Polaroid sheet
allows light pass through only if the E-field vector is
in a specific direction.

19. For unpolarized light, a polaroid sheet reduces its intensity θ
I = I0cos2θ
Intensity after polaroid
Intensity before polaroid
For unpolarized light, a polaroid sheet reduces its intensity
to half (sunglasses).

21. Light Scattering
Long wavelength
Short wavelength

22. Starting from A, make one touch at the wall and finish at B.
Which path takes the shortest time?
θ θ
x A
x B

23. Who has the better chance to save this
drowning guy?
Pam Anderson
David Hasselhoff
Jeremy Jackson
Pamela Anderson

24. Reflection and Mirrors
qi = qr qi qr
Law of reflection
Specular Reflection
Diffuse Reflection

25. Image forms at the point where the light rays converge.
When we talk about an image, start from an ideal point light source.
Every object can be constructed as a collection of point light sources.
VIRTUAL
IMAGE q p
Image forms at the point where the light rays converge.
When real light rays converge  Real Image
When imaginary extension of L.R. converge  Virtual Image
Only real image can be viewed on screen placed at the spot.

26. How about left-right? Let’s check?p q
IMAGE
VIRTUAL
For plane mirror: p = q
How about left-right? Let’s check?