( i ) An object is plated at a position p > f from a concave mirror as shown in Figure CQ39.12a, where f is the focal length of the mirror. In a finite time interval, the object is moved to the right to a position at the focal point F of the mirror. Show that the image of the object moves at a speed greater than the speed of light . ( ii ) A laser pointer is suspended in a horizontal plane and set into rapid rotation as shown in Figure CQ39 12b. Show that the spot of light it produces on a distant screen can move across the screen at a speed greater than the speed of light. (If you carry out this experiment. make sure the direct laser light cannot enter a person's eyes.) ( iii ) Argue that the experiments in parts (i) and (ii) do not invalidate the principle that no material, no energy, and no information can move faster than light moves in a vacuum. Figure CQ39.12
( i ) An object is plated at a position p > f from a concave mirror as shown in Figure CQ39.12a, where f is the focal length of the mirror. In a finite time interval, the object is moved to the right to a position at the focal point F of the mirror. Show that the image of the object moves at a speed greater than the speed of light . ( ii ) A laser pointer is suspended in a horizontal plane and set into rapid rotation as shown in Figure CQ39 12b. Show that the spot of light it produces on a distant screen can move across the screen at a speed greater than the speed of light. (If you carry out this experiment. make sure the direct laser light cannot enter a person's eyes.) ( iii ) Argue that the experiments in parts (i) and (ii) do not invalidate the principle that no material, no energy, and no information can move faster than light moves in a vacuum. Figure CQ39.12
Solution Summary: The author explains how the image of the object moves at a speed greater than the speed of light.
(i) An object is plated at a position p > f from a concave mirror as shown in Figure CQ39.12a, where f is the focal length of the mirror. In a finite time interval, the object is moved to the right to a position at the focal point F of the mirror. Show that the image of the object moves at a speed greater than the speed of light. (ii) A laser pointer is suspended in a horizontal plane and set into rapid rotation as shown in Figure CQ39 12b. Show that the spot of light it produces on a distant screen can move across the screen at a speed greater than the speed of light. (If you carry out this experiment. make sure the direct laser light cannot enter a person's eyes.) (iii) Argue that the experiments in parts (i) and (ii) do not invalidate the principle that no material, no energy, and no information can move faster than light moves in a vacuum.
Figure CQ39.12
Definition Definition Rate at which light travels, measured in a vacuum. The speed of light is a universal physical constant used in many areas of physics, most commonly denoted by the letter c . The value of the speed of light c = 299,792,458 m/s, but for most of the calculations, the value of the speed of light is approximated as c = 3 x 10 8 m/s.
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
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