Physics 2130
Final Examination
Spring 2006
1- A transverse sinusoidal wave is generated at one end of a long, horizontal string by a
bar that moves up and down through a distance of 1.6 cm. The motion is continuous and
is repeated regularly 150 times per second. The string has linear density 220 g/m and is
kept under a tension of 140 N. Find the maximum value of (a) the transverse speed u and
(b) the transverse acceleration; and (c) the wavelength of the wave.
-----------------------------------------------------------------------------------------------------------2 - A jet plane passes over you at a height of 5070 m and a speed of Mach 1.39. (a) Find
the Mach cone angle. (b) How long after the jet passes directly overhead does the shock
wave reach you? Use 331 m/s for the speed of sound.
---------------------------------------------------------------------------------------------------------3- A tuning fork of unknown frequency makes 3.00 beats per second with a standard fork
of frequency 384 Hz. The beat frequency decreases when a small piece of wax is put on a
prong of the first fork. What is the frequency of this fork?
-----------------------------------------------------------------------------------------------------------4- The maximum electric field 10 m from an isotropic point source of light is 2.0 V/m.
What are (a) the maximum value of the magnetic field and (b) the average intensity of the
light there? (c) What is the power of the source? μ0 =4π 10-7 T.m/A
-----------------------------------------------------------------------------------------------------------5 - Unpolarized light is sent into a system of two polarizing sheets. The angles θ1 and θ2
of the polarizing directions of the sheets are measured counterclockwise from the positive
direction of the y axis (they are not drawn to scale in the figure). Angle θ1 is fixed but
angle θ2 can be varied. Figure below gives the intensity of the light emerging from sheet
2 as a function of θ2. (The scale of the intensity axis is not indicated.) What percentage of
the light's initial intensity is transmitted by the two-sheet system when θ2 = 90°?
Physics 2130
Final Examination
Spring 2006
6- A 2.00-m-long vertical pole extends from the bottom of a swimming pool to a point
50.0 cm above the water. Sunlight is incident at angle θ = 55.0°. What is the length of the
shadow of the pole on the level bottom of the pool? nwater=1.33.
7- A sand grain is 3.00 cm from thin lens 1, on the central axis through the two
symmetric lenses. The distance between focal point and lens is 4.00 cm for both lenses;
the lenses are separated by 8.00 cm. (a) What is the distance between lens 2 and the
image it produces of the sand grain? Is that image (b) to the left or right of lens 2, (c) real
or virtual, and (d) inverted relative to the sand grain or not inverted?
8- A broad beam of light of wavelength 683 nm is sent directly downward through the
top plate of a pair of glass plates. The plates are 120 mm long, touch at the left end, and
are separated by 48.0 mm at the right end. The air between the plates acts as a thin film.
How many bright fringes will be seen by an observer looking down through the top
plate?
9- (a) In a double-slit experiment, what ratio of d to a causes diffraction to eliminate the
fourth bright side fringe? (b) What other bright fringes are also eliminated? 31
Physics 2130
Final Examination
Spring 2006
10- Show that if a spherical refracting surface with an index of refraction n2 placed in a
medium with an index of refraction n1 the following expression holds:
Here p is the object distance, i is the image distance and r is the radius of the spherical
refracting surface. Assume rays make small angles with the central axis of the surface.
11- Standing waves are produced by the interference of two traveling sinusoidal waves,
each of frequency 100 Hz. The distance from the 2nd node to the 5th node is 60 cm. The
wavelength of each of the two original waves is:
1- 50 cm
2- 40 cm
3- 30 cm
4- 20 cm
5- 15 cm
12- A 40-cm long string, with one end clamped and the other free to move transversely, is
vibrating in its fundamental standing wave mode. If the wave speed is 320 cm/s the
frequency is:
1- 32 Hz
2- 16 Hz
3- 8 Hz
4- 4 Hz
5- 2 Hz
13- If the sound level is increased by 10 db the intensity increases by a factor of:
1- 2
2- 5
3- 10
4- 20
5- 100
Physics 2130
Final Examination
Spring 2006
14- Two pipes are each open at one end and closed at the other. Pipe A has length L and
pipe B has length 2L. Which harmonic of pipe B matches in frequency the fundamental
of pipe A?
1- The second
2- The third
3- There are none
4- The fourth
5- The fundamental
15- Light of uniform intensity shines perpendicularly on a totally absorbing surface, fully
illuminating the surface. If the area of the surface is decreased:
1- the radiation pressure decreases and the radiation force decreases
2- the radiation pressure increases and the radiation force decreases
3- the radiation pressure increases and the radiation force increases
4- the radiation pressure stays the same and the radiation force increases
5- the radiation pressure stays the same and the radiation force decreases
16- The index of refraction of benzene is 1.80. The critical angle for total internal
reflection, at a benzene-air interface, is about: 3
1- 56°
2- 47°
3- 34°
4- 22°
5- 18°
17- An erect object is placed on the central axis of a thin lens, further from the lens than
the magnitude of its focal length. The magnification is +0.4. This means: 1
1- the image is virtual and erect, and the lens is a diverging lens
2- the image is real and inverted and the lens is a converging lens
3- the image is virtual and erect, and the lens is a converging lens
4- the image is virtual and inverted and the lens is a diverging lens
5- the image is real and erect and the lens is a converging lens
Physics 2130
Final Examination
Spring 2006
18- The bellows of an adjustable camera can be extended so that the largest film to lens
distance is one and one-half times the focal length. If the focal length is 12 cm, the
nearest object which can be sharply focused on the film must be what distance from the
lens? 3
1- 12 cm
2- 24 cm
3- 36 cm
4- 48 cm
5- 72 cm
19- Waves from two slits are in phase at the slits and travel to a distant screen to produce
the third side maximum of the interference pattern. The difference in the distance traveled
by the waves is: 4
1- half a wavelength
2- a wavelength
3- three halves of a wavelength
4- two wavelengths
5- five halves of a wavelength
20- Monochromatic light is normally incident on a diffraction grating that is 1 cm wide
and has 10,000 slits. The first order line is deviated at a 30° angle. What is the
wavelength, in nm, of the incident light? 3
1- 300
2- 400
3- 500
4- 600
5- 1000