Police radar detects the speed of a car (Fig. P38.15) as follows. Microwaves of a precisely known frequency are broadcast toward the car. The moving car reflects the microwaves with a Doppler shift. The reflected waves are received and combined with an attenuated version of the transmitted wave. Beats occur between the two microwave signals. The beat frequency is measured. (a) For an electromagnetic wave reflected back to its source from a mirror approaching at speed v , show that the reflected wave has frequency f ′ = c + v c − v f where f is the source frequency. (b) Noting that v is much less than c , show that the beat frequency can be written as f beat = 2 v/λ . (c) What beat frequency is measured for a car speed of 30.0 m/s if the microwaves have frequency 10.0 GHz? (d) If the beat frequency measurement in part (c) is accurate to ±5.0 Hz, how accurate is the speed measurement?
Police radar detects the speed of a car (Fig. P38.15) as follows. Microwaves of a precisely known frequency are broadcast toward the car. The moving car reflects the microwaves with a Doppler shift. The reflected waves are received and combined with an attenuated version of the transmitted wave. Beats occur between the two microwave signals. The beat frequency is measured. (a) For an electromagnetic wave reflected back to its source from a mirror approaching at speed v , show that the reflected wave has frequency f ′ = c + v c − v f where f is the source frequency. (b) Noting that v is much less than c , show that the beat frequency can be written as f beat = 2 v/λ . (c) What beat frequency is measured for a car speed of 30.0 m/s if the microwaves have frequency 10.0 GHz? (d) If the beat frequency measurement in part (c) is accurate to ±5.0 Hz, how accurate is the speed measurement?
Police radar detects the speed of a car (Fig. P38.15) as follows. Microwaves of a precisely known frequency are broadcast toward the car. The moving car reflects the microwaves with a Doppler shift. The reflected waves are received and combined with an attenuated version of the transmitted wave. Beats occur between the two microwave signals. The beat frequency is measured. (a) For an electromagnetic wave reflected back to its source from a mirror approaching at speed v, show that the reflected wave has frequency
f
′
=
c
+
v
c
−
v
f
where f is the source frequency. (b) Noting that v is much less than c, show that the beat frequency can be written as fbeat = 2v/λ. (c) What beat frequency is measured for a car speed of 30.0 m/s if the microwaves have frequency 10.0 GHz? (d) If the beat frequency measurement in part (c) is accurate to ±5.0 Hz, how accurate is the speed measurement?
Interaction between an electric field and a magnetic field.
Plastic beads can often carry a small charge and therefore can generate electric fields. Three beads are oriented such that
system of all three beads is zero.
91
E field lines
93
92
What charge does each bead carry?
91
92
-1.45
=
=
What is the net charge of the system? What charges have to be equal? μC
2.9
×
What is the net charge of the system? What charges have to be equal? μC
93 = 2.9
μС
92
is between and
91 93°
The sum of the charge on q₁ and 92 is 91 + 92 = −2.9 μC, and the net charge of the
Chapter 39 Solutions
Physics for Scientists and Engineers, Technology Update (No access codes included)
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.