Light bulbs are often assumed to obey Ohm's law. However, this is not really true because their resistance increases substantially as the filament heats up in its "working" state. A typical flashlight bulb at full brilliance draws a current of approximately 0.5 when connected to a 3- voltage source. For this problem, assume that the changing resistance causes the current to be 0.5 for any voltage between 2 and 3 . Suppose this flashlight bulb is attached to a capacitor as shown in the circuit from the problem introduction. If the capacitor has a capacitance of 3 (an unusually large but not unrealistic value) and is initially charged to 3 , how long will it take for the voltage across the flashlight bulb to drop to 2 (where the bulb will be orange and dim)? Call this time . Express numerically in seconds to the nearest integer.

Aparticle with mass 1.81×10−3 kg and a charge of 1.22×10−8 c has, at a given instant, a velocity v⃗ =(3.00×104m/s)j^. what are the magnitude and direction of the particle’s acceleration produced by a uniform magnetic field b⃗ =(1.63t)i^+(0.980t)j^?

19. explain why a magnet from your refrigerator could not be used to lift something as heavy as a car. (chapter 7 – pages 202-203) 20. can a magnet ever have a single pole? explain your answer. (chapter 7 – page 208) 21. what happens to the wavelength of a wave if the frequency is increased? (chapter 9 – pages 280-281) 22. an ocean wave has a wavelength of 10 m and a frequency of 4.0 hz. what is the velocity of the wave? show the appropriate equation from your book and show your work with units. (chapter 9 – page 282) 23. as you sit outside, the sound of a siren becomes lower in pitch. is the emergency vehicle moving away from or towards you? explain how you know. (chapter 10 – page 315-316) 24. why are two astronauts in space unable to hear one another? (chapter 10 – page 307) 25. explain in at least 3 sentences how electromagnetic waves form. (chapter 11 – page 338-339) 26. using the chart on page 345 in your textbook, what are the three types of electromagnetic wave with wavelengths shorter than those of visible light. give an example of each. (chapter 11 – pages 345-351) 27. explain why a leaf usually appears to be green, but a rose typically appears red. (chapter 12 – page 373) 28. what is the difference in light that is refracted compared to light that is reflected? think in terms of speed of light as well as what happens to light waves when they interact with a medium. (chapter 12 – pages 369-370) 29. how are concave and convex lenses different? (chapter 13 – page 408-410) 30. what type of mirror is used in rearview mirrors in cars? why is it important that these mirrors have the warning, “objects in mirror are closer than they appear.”? (chapter 13 – page 405)

**urgent** roberto plans to use two transformers to reduce a voltage of 120 v to 4 v. he uses a transformer that has 300 coils in the primary winding and 50 coils in the secondary winding. he has four other transformers, as listed in the table. which transformer should roberto use to have an ending voltage of 4 v? a- w b-xc- yd- z