Physics 203 at Portland State 2014

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exam_2_review [2014/05/10 02:24]
wikimanager [Review problem 3]
exam_2_review [2014/05/14 14:48] (current)
wikimanager [Review problem 3] added solution
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====Review question 1==== ====Review question 1====
The focal lengths of the objective and the eyepiece in a microscope are 0.29 cm and 2.5 cm, respectively. An object is placed 0.3 cm from the objective. The image of this object is viewed with the eyepiece adjusted for minimum eyestrain. What is the distance between the objective and the eyepiece? ​ The focal lengths of the objective and the eyepiece in a microscope are 0.29 cm and 2.5 cm, respectively. An object is placed 0.3 cm from the objective. The image of this object is viewed with the eyepiece adjusted for minimum eyestrain. What is the distance between the objective and the eyepiece? ​
-    * [....] A) 11.2 cm +    * [ <color green>​X</​color> ​] A) 11.2 cm
* [....] B) 10.1 cm      * [....] B) 10.1 cm
* [....] C) 10.4 cm      * [....] C) 10.4 cm
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====Review question 2==== ====Review question 2====
A magnifying glass uses a converging lens with a refractive power of 20 diopters. What is the magnification if the image is to be viewed by a relaxed eye with a near point of 25 cm?  A magnifying glass uses a converging lens with a refractive power of 20 diopters. What is the magnification if the image is to be viewed by a relaxed eye with a near point of 25 cm?
-  * [....] A) 5.0+  * [ <color green>​X</​color> ​] A) 5.0
* [....] B) 4.0   * [....] B) 4.0
* [....] C) 1.0   * [....] C) 1.0
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* [....] C) $+2.5$ diopters ​   * [....] C) $+2.5$ diopters ​
* [....] D) $+2.7$ diopters ​   * [....] D) $+2.7$ diopters ​
-  * [....] E) $-2.5$ diopters ​+  * [ <color green>​X</​color> ​] E) $-2.5$ diopters ​

<color green></​color>​ <color green></​color>​
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* [....] A) Convex. ​   * [....] A) Convex. ​
* [....] B) Plane. ​   * [....] B) Plane. ​
-  * [....] C) Concave. ​+  * [ <color green>​X</​color> ​] C) Concave. ​
* [....] D) All of the given answers would work equally as well.    * [....] D) All of the given answers would work equally as well.
* [....] E) None of the given answers would burn a hole.    * [....] E) None of the given answers would burn a hole.
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You have a choice between two lenses of focal lengths $f_a$ and $f_b = 2 f_a$ to use as objective lens in building a compound microscope. If the magnification you obtain using lens //a// is $M_a$, what will be the magnification when using lens //​b//? ​ You have a choice between two lenses of focal lengths $f_a$ and $f_b = 2 f_a$ to use as objective lens in building a compound microscope. If the magnification you obtain using lens //a// is $M_a$, what will be the magnification when using lens //​b//? ​
* [....] A) $M_b = \frac{1}{4} M_a$   * [....] A) $M_b = \frac{1}{4} M_a$
-  * [....] B) $M_b = \frac{1}{2} M_a$+  * [ <color green>​X</​color> ​] B) $M_b = \frac{1}{2} M_a$
* [....] C) $M_b = 8 M_a$   * [....] C) $M_b = 8 M_a$
* [....] D) $M_b = 4 M_a$    * [....] D) $M_b = 4 M_a$
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Which of the following expressions is correct for the transmitted intensity of an unpolarized beam of light with an intensity $I_i$ passing through a polarizer? ​ Which of the following expressions is correct for the transmitted intensity of an unpolarized beam of light with an intensity $I_i$ passing through a polarizer? ​
* [....] A) $I_t = 2 I_i$   * [....] A) $I_t = 2 I_i$
-  * [....] B) $I_t = \frac{1}{2} I_i$+  * [ <color green>​X</​color> ​] B) $I_t = \frac{1}{2} I_i$
* [....] C) $I_t = I_i$   * [....] C) $I_t = I_i$
* [....] D) $I_t = 4 I_i$   * [....] D) $I_t = 4 I_i$
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* [....] A) neither spherical nor chromatic aberration. ​   * [....] A) neither spherical nor chromatic aberration. ​
* [....] B) chromatic aberration, but not spherical aberration. ​   * [....] B) chromatic aberration, but not spherical aberration. ​
-  * [....] C) spherical aberration, but not chromatic aberration.+  * [ <color green>​X</​color> ​] C) spherical aberration, but not chromatic aberration.
* [....] D) both spherical and chromatic aberration. ​   * [....] D) both spherical and chromatic aberration. ​

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* [....] B) $4.8$ m    * [....] B) $4.8$ m
* [....] C) $4.2$ m    * [....] C) $4.2$ m
-  * [....] D) $-4.2$ m +  * [ <color green>​X</​color> ​] D) $-4.2$ m
* [....] E) $5.2$ m    * [....] E) $5.2$ m

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* [....] B) $-36.4$ cm   * [....] B) $-36.4$ cm
* [....] C) $-21.2$ cm   * [....] C) $-21.2$ cm
-  * [....] D) $+36.4$ cm+  * [ <color green>​X</​color> ​] D) $+36.4$ cm
* [....] E) $+21.2$ cm   * [....] E) $+21.2$ cm

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====Review question 10==== ====Review question 10====
An object is placed in front of a convex mirror at a distance larger than twice the focal length of the mirror. The image will appear ​ An object is placed in front of a convex mirror at a distance larger than twice the focal length of the mirror. The image will appear ​
* [....] A) upright and enlarged.  ​   * [....] A) upright and enlarged.  ​
-  * [....] B) upright and reduced.+  * [ <color green>​X</​color> ​] B) upright and reduced.
* [....] C) inverted and enlarged.   * [....] C) inverted and enlarged.
* [....] D) inverted and reduced.  ​   * [....] D) inverted and reduced.  ​
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* [....] A) 2.0    * [....] A) 2.0
* [....] B) 1.5    * [....] B) 1.5
-  * [....] C) 1.0 +  * [ <color green>​X</​color> ​] C) 1.0
* [....] D) 0.25   * [....] D) 0.25
* [....] E) 0.5    * [....] E) 0.5
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====Review question 12==== ====Review question 12====
A vertically polarized beam of light of intensity $100\frac{\text W}{\,{\text m}^2}$ passes through a polarizer with its transmission axis at 40.0$^\circ$ to the vertical. What is the transmitted intensity of this beam of light? ​ A vertically polarized beam of light of intensity $100\frac{\text W}{\,{\text m}^2}$ passes through a polarizer with its transmission axis at 40.0$^\circ$ to the vertical. What is the transmitted intensity of this beam of light? ​
-  * [....] A) $58.7\frac{\text W}{\,{\text m}^2}$ ​+  * [ <color green>​X</​color> ​] A) $58.7\frac{\text W}{\,{\text m}^2}$ ​
* [....] B) $0\frac{\text W}{\,{\text m}^2}$ ​   * [....] B) $0\frac{\text W}{\,{\text m}^2}$ ​
* [....] C) $100\frac{\text W}{\,{\text m}^2}$ ​   * [....] C) $100\frac{\text W}{\,{\text m}^2}$ ​
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* [....] A) 200 cm    * [....] A) 200 cm
* [....] B) 101 cm    * [....] B) 101 cm
-  * [....] C) 198 cm +  * [ <color green>​X</​color> ​] C) 198 cm
* [....] D) 202 cm    * [....] D) 202 cm
* [....] E) 2.0 cm   * [....] E) 2.0 cm
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* [....] C) half as large as his face    * [....] C) half as large as his face
* [....] D) four times as large as his face    * [....] D) four times as large as his face
-  * [....] E) three times as large as his face+  * [ <color green>​X</​color> ​] E) three times as large as his face

<color green></​color>​ <color green></​color>​
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* [....] B) a short focal length objective and a long focal length eyepiece.   * [....] B) a short focal length objective and a long focal length eyepiece.
* [....] C) a short focal length objective and a short focal length eyepiece. ​   * [....] C) a short focal length objective and a short focal length eyepiece. ​
-  * [....] D) a long focal length objective and a short focal length eyepiece.+  * [ <color green>​X</​color> ​] D) a long focal length objective and a short focal length eyepiece.

<color green></​color> ​ <color green></​color> ​
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- A lens with a negative focal length.   - A lens with a negative focal length.
-    * <color green>...</​color> ​+    * <color green>diverging lens</​color> ​
- A problem in lenses where different colors of light are focused to different focal points. ​   - A problem in lenses where different colors of light are focused to different focal points. ​
-    * <color green>...</​color> ​+    * <color green>chromatic aberration</​color> ​
- The angle of incidence of light such that after striking a surface the reflected light is completely polarized.   - The angle of incidence of light such that after striking a surface the reflected light is completely polarized.
-    * <color green>...</​color> ​+    * <color green>Brewster'​s angle</​color> ​
- Reflection from a rough surface such that light is sent out in a variety of directions.   - Reflection from a rough surface such that light is sent out in a variety of directions.
-    * <color green>...</​color> ​+    * <color green>diffuse reflection</​color> ​
- Light rays converge towards this type of object. The sign convention for the distance to the object in this case is negative.   - Light rays converge towards this type of object. The sign convention for the distance to the object in this case is negative.
-    * <color green>...</​color> ​+    * <color green>virtual object</​color> ​
- The ability of a lens to refract light (commonly measured in diopters)   - The ability of a lens to refract light (commonly measured in diopters)
-    * <color green>...</​color> ​+    * <color green>refractive power</​color> ​
- A problem in lenses and mirrors of a particular shape where light further away from the principal axis is focused to a different point than light closer to the principal axis.   - A problem in lenses and mirrors of a particular shape where light further away from the principal axis is focused to a different point than light closer to the principal axis.
-    * <color green>...</​color> ​+    * <color green>spherical aberration</​color> ​
- The length of this device is the sum of the two focal lengths of the lenses used to make it   - The length of this device is the sum of the two focal lengths of the lenses used to make it
-    * <color green>...</​color> ​+    * <color green>telescope</​color> ​
- A property of a material that is related to how fast light travels in the material   - A property of a material that is related to how fast light travels in the material
-    * <color green>...</​color> ​+    * <color green>index of refraction</​color> ​
- Colorful object seen in the sky due to the dispersion of light in raindrops.   - Colorful object seen in the sky due to the dispersion of light in raindrops.
-    * <color green>...</​color> ​+    * <color green>rainbow</​color> ​

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====Review problem 4==== ====Review problem 4====
-The air pressure variations in a sound wave cause the eardrum ​(tympanic membrane to vibrate+While wandering on Mars (which has little atmosphere and can be considered a vacuum environment), you stumble upon a mysterious cube of an unknown material. You have a red and a blue laser handy and perform a few experiments. You observe that total internal reflection occurs at the critical angle of 19.5$^\circ$ for red light
-  - For given vibration amplitude, are the maximum velocity and acceleration ​of the eardrum greatest for high frequency sounds or low frequency sounds? (1 pts+  - To observe total internal reflection did you scrutinize ​ray of light going from the mystery material to vacuum or a ray of light going from vacuum to the mystery material ( 1 pt
-    * <color green>$v_\text{max}$ $=x_\text{max}\omega$</​color>​ +    * <color green>...</​color>​
-    * <color green>​$a_\text{max}$ $=x_\text{max}\omega^2$</​color>​ +  - What is the index of refraction ​of the material ​for red light? ​(pts)
-    * <color green>​the greatest values are for the high-frequency sound</​color>​ +    * <color green>​...</​color>​
-  - Find the maximum velocity and the maximum acceleration ​of the eardrum ​for vibrations of amplitude $1.0\times 10^{-8}\,$m at a frequency of 20.0 kHz. (pts)  +      * <color green>...</​color>​
-    * <color green>$v_\text{max}$ $=x_\text{max}\omega$ $=x_\text{max}(2\pi f)$ $=1.0\times 10^{-8}\,​$m$\,​\cdot\,​6.283\cdot 20\times 10^3\,$Hz $=1.26\times 10^{-3}\frac{\text m}{\text s}$ </​color>​ +  - What is the speed of red light in the material? (pts)
-    * <color green>$a_\text{max}$ $=x_\text{max}\omega^2$ $=x_\text{max}(2\pi f)^2$ $=1.0\times 10^{-8}\,​$m$\,​\cdot\,​(6.283\cdot 20\times 10^3\,​$Hz$)^2=158\,​\frac{\text m}{\,{\text s}^2}$ ​</​color>​ +    * <color green>...</​color>​
-  - What is the period of a complete oscillation ​of the ear drum at this frequency? (pts) +      * <color green>...</​color>​
-    * <color green>$T=\frac{1}{f}$ $=\frac{1}{20\times 10^3\,​{\text{Hz}}}$ $=5.0\times 10^{-5}\,$s</​color>​ +  - What is Brewster'​s angle for red light going from vacuum to the mystery material? (3 pts)
-  - Using a crude model of the eardrum as a mass (3.0 mg) on a spring, what would be the spring constant of the eardrum, assuming the resonance frequency of 20.0 kHz? (3 pts) +    * <color green>...</​color>​
-    ​* <color green>$T=2\pi\sqrt{\frac{m}{k}}$</​color>​ +      * <color green>​...</​color>​
-    * <color green>$\left(\frac{T}{2\pi}\right)^2=\frac{m}{k}$</​color>​ +  - Would the critical angle for blue light be greater or smaller than that of red light? ​(1 pt). Why? (pts) (Hint: You can safely make the assumption that this mystery material behaves like glass for the frequency dependence of the index of refraction.)
-    * <color green>$k=\frac{4\pi^2m}{T^2}$ $=\frac{4\,​\cdot\,​3.14159^2\,​\cdot\,​3.0\times 10^{-6}\,​{\text{kg}}}{\big(5.0\times 10^{-5}\,​{\text s}\big)^2}$ $=4.74\times 10^4\frac{\text N}{\text m}$</​color>​ +    * <color green>...</​color>​
-  - The ear canal (external auditory canal) can be modeled as a tube with one closed end. If the length ​of the ear canal is 25 mm long and the speed of sound in air is 340 m/s, what is the fundamental ​(1<​sup>​st</​sup>​ harmonicof the ear canal? (pts)  +
-    * <color green>$f_1=\frac{v}{4L}$ $=\frac{340\,​\frac{\text m}{\text s}}{4\,​\cdot\,​25\times 10^{-3}\,​{\text m}}$ $=3400\,$Hz</​color>​+

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