Test 3 Practice Problems (Ch 21 – 24)
Ch 21 – AC Circuits
1) Reactance
Find the capacitive reactance and inductive reactance if the capacitance is 10 µF and the inductance is 10 mH.
The frequency is 2000 Hz.
2) RMS
Find the RMS voltage is the peak voltage is 12 V. Find the peak current if the RMS current is 8.0 A.
Ch 22 – Reflection and Refraction of Light
1) You point a laser beam to the surface of a fish tank as shown in the figure. Find the angle β at which the
beam exits through the side of the tank (you can ignore the effect of the glass wall). The index of refraction of
water is 1.33
Ch 23 – Mirrors and Lenses
1) In the following example of a concave mirror find the position of the image and describe it (virtual, real,
upright, inverted, larger, smaller, etc)
2) You are standing 4.0 m from a convex security mirror in a store. Your image looks 0.35 times your actual
size. What is the focal length (f) of the mirror?
3) Image formation by a converging lens. We buy a magnifying glass that has a power of 2.5 D. If we place
an object 30.0 cm away from the lens, where is the image formed (find d i ) and what kind of image is it (real,
virtual, upright, inverted)?
Ch 24 – Wave Optics
1) Double Slit
A parallel beam of light from a He-Ne laser, with a wavelength of 656 nm, falls on two very narrow slits
that are 0.050 mm apart. How far apart are the fringes in the center of the pattern on a screen 4.2 m away?
2) Single Slit
In an experiment you shine red light of wavelength 533 nm on a slit, generating a central diffraction peak
of 2θ = 8.4o as shown in the figure. How wide is the slit?
3) Diffraction Grating
A diffraction grating has lines separated by 3.5 μm. Calculate the angle of diffraction of the first order
fringe for green light (λ = 530 nm) and red light (λ = 650 nm).
4) Diffraction Grating
A diffraction grating is used to determine wavelengths in a spectrometer. Calculate the angular separation
(in degrees) between the two main lines of sodium (589.0 nm and 589.6 nm) if the grating has a density of
15,000 lines per inch. [1 inch = 2.54 cm]
5) Polarization
Find how much intensity of a beam of un-polarized light will go through three polarizers, where the first
and second are rotated 37o with respect to each other and the second and third are also rotated 37o with
respect to each other.