( 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.
Example
Two charges, one with +10 μC of charge, and
another with - 7.0 μC of charge are placed in
line with each other and held at a fixed distance
of 0.45 m. Where can you put a 3rd charge of +5
μC, so that the net force on the 3rd charge is
zero?
*
Coulomb's Law Example
Three charges are positioned as seen below. Charge
1 is +2.0 μC and charge 2 is +8.0μC, and charge 3 is -
6.0MC.
What is the magnitude and the direction of the force
on charge 2 due to charges 1 and 3?
93
kq92
F
==
2
r13 = 0.090m
91
r12 = 0.12m
92
Coulomb's Constant: k = 8.99x10+9 Nm²/C²
✓
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