LIGHT AND COLOR

Physics 134 November 12, 2002

Exam 2 H. Fenichel

This examination consists of thirty (30) questions.  Mark your answers with a No. 2 pencil on the answer sheet.  Be sure to enter your name and student number.  Also mark the appropriate spaces under your name and ID at the bottom of the page.

Useful Relations

1. c = ln c = 3 x 10⁸ m/sec Speed of light

2. E = hn h = 6.7 x 10^‑34 joule‑sec Photon energy

3. I ~ A² Intensity

4. q₁= q₁' Reflection

5. n₁ sin q₁ = n₂ sin q₂ n = c/v Refraction

6. (1/s) + (1/i) = (1/f) lens equation

7. M = (h_i/h_s) = i/s magnification

8. M_T = f_o/f_e telescope

9. M_M = 450/(f_of_e) microscope

10. d (diopter) = 1/f(meters) optical power

11. f_e = s T⁴ (s = 6 x 10^‑8 w/m²K⁴) Radiant Flux

12. E_v = I_v/s² illuminance

13. ^oF = (9/5)^oC + 32^o T(K)=T(^oC+273^o) temperature conversion

14. f/ = (f/D) "f" Number

---------------------------------------------------------------Table of Luminous Efficacy

l (nm) V_l 683 V_l (lm/W)

400 .0004 .3

450 .0380 26

500 .3230 220

550 .9950 680

600 .6310 430

650 .1070 73

700 .0041 3

---------------------------------------------------------------

1. A laser light source produces 10 mW at λ = 550 nm. The luminous flux produced by this laser is:

A) .9950 lm B) 680 lm C) 6.8 lm D)550 lm

2) In the table on the previous page the numbers in the last column are values of

A) luminous flux B) sensitivity C) radiant flux

D) luminous efficacy

3) The properties of the laser depend on

A) fluorescence B) stimulated emission C) incandescence

D) all of the above

4) When the temperature of a blackbody is tripled the energy radiated will increase by a factor of

A) 3 B) 16 C) 27 D) 81

5) Transitions of electrons between a pair of their energy levels accounts for

A) monochromatic (single wavelength) light B) white light

C) a discrete spectrum D) a continuous spectrum E) ultraviolet light

6) A real image may be formed by

A) a concave mirror B) a diverging lens C) a plane mirror D) all of the above E) none of the above

7) An object is placed 30 cm in front of a lens with a focal length of 15 cm. The magnification of this lens is

A) 1 B) 2 C) 15 D) 1/2

8) A student who is 5 feet tall wishes to install a "full length" mirror so that she can examine her appearance from head to toe. The smallest possible height of the mirror is:

A) 6 ft B) 2 ft C) 5 ft D) 3 ft E) 2ft. 6in.

9) Almost all of the electromagnetic spectrum is visible

A) true B)false

10) You are walking towards a concave mirror. As you cross the focal point:

A) Your inverted real image changes to an inverted virtual image.

B) Your eyes cross.

C) Your inverted virtual image changes to an upright real image.

D) Your inverted real image changes to an upright virtual image.

E) Your upright virtual image changes to an upright real image.

11) An object located 10 in. away from a lens has an image located 15 in. away from the lens on the same side. The focal length of the lens is:

A) 5 in B) 30 in C)3 in D 10 in E) 6 in

12) Light from the sun has more relative intensity in the infrared than light from and incandescent bulb

A) true B)false

13) A simple astronomical refracting telescope is constructed of two lenses, of focal lengths 20 cm and 2 cm, respectively. The magnifying power of the telescope is approximately:

A) 10 B) 5 C) 2 D) 20 E) None of these

14) The compound microscope and the refracting astronomical telescope are both two-lens systems, basically. Their eyepieces may be the same; the big difference between them is in the focal length and diameter of the objective lens.

A) True B) False

15) When looking at pebbles in a pond they appear to be

A) closer to the surface

B) further away from the surface

C) the same distance from the surface as compared to their appearance if the pond were drained of water.

16) A virtual image may be formed by

A) a mirror B) a diverging lens C) a convex lens

D) all of the above E) none of the above

17) Total internal reflection can take place when light moves from a medium of low index of refraction to a medium of higher index of refraction.

A) True B) False

18) The speed of light in vacuum is 3X10⁸ m/s. In glass of refractive index 1.50, the speed of light is:

A) 3X10⁸ m/s B) 1.5X10⁸ m/s C) 2X10⁸ m/s D) 186,000 Miles/sec

E) None of these

19) Blacbody radiation is

A) colorless B) caused by stimulated emission C) polarized

D) depends on the temperature of the radiator E) none of the above

20) A 15 watt bulb delivers how much power?

A) 15 joules/ sec B) 15 Ev/ sec C) 150 joules/ sec

D) 1.6 x 10 –19 joules/ sec E) 1.5 joules/ sec 5

21) A converging lens may be used as a magnifier

A) True B) False

22 ) The image formed by a positive, convex lens is

A) inverted B) erect C) can be either A) or B)

23) The magnification of a telescope can be increased by increasing the focal length of the objective lens.

A) True B) False

24) If two light bulbs are rated at 100 watts, this means that

A) they cost the same to operate

B) they produce the same amount of visible light

C) they each produce 100 watts of visible light

D) their peak is in the visible range

25) The boiling point of water on the Kelvin scale is

A) 212 B) 100 C) 373 D) ‑273 degrees.

26) Two light sources are said to have the same "color temperature".  This means that the two sources must be at the same temperature.

A) true B) false

27) Blackbody radiation is

A) colorless B) is caused by stimulated emission

C) is polarized D) depends on the temperature of the radiator

E) none of the above

28) The light emitted by the phosphor in a fluorescent tube is centered at

A) the same B) a greater C) a lower

wavelength than the corresponding emission line of mercury

29) An essential difference between the light emitted from fluorescent and incandescent bulbs is that

A)The fluorescent bulb spectrum has discrete and continuous components, whereas the incandescent bulb spectrum has only a continuous component.

B)The fluorescent bulb spectrum is discrete, whereas the incandescent bulb spectrum is continuous.

C) the fluorescent light is polarized, whereas the incandescent light is not.

D) the fluorescent light is coherent, whereas the incandescent light is not.

30) The term laser is

A) an acronym for "light amplification by the spontaneous emission of

radiation".

B) not an acronym, and relates to spontaneous emission.

C) an acronym for "light amplification by the stimulated emission of

radiation".

D) an acronym for "light attenuation by the stimulated emission of radiation".