18) When you swipe a credit card, the machine sometimes fails to read the card. What can you do differently? a) Swipe the card more slowly so that the reader has more time to read the magnetic stripe. b) Swipe the card more quickly so that the induced emf is higher. c) Swipe the card more quickly so that the induced currents are reduced. d) Swipe the card more slowly so that the magnetic field don't change so fast. 19) Which of the following travel at the same speed as light? (Choose all that apply) a) Radio waves b) Microwaves c) Radar d) ultrasonic waves e) Infrared radiation g) Gamma rays h) x-rays f) cell phone signals 20) In empty space, which quantity is always larger for x-ray radiation than for a radio wave? a) amplitude b) wavelength c) frequency d) speed 21) An electromagnetic wave is traveling straight down toward the center of the earth. At a certain moment in time the electric field points west. In which direction does the magnetic field point at this moment?

18) When you swipe a credit card, the machine sometimes fails to read the card. What can you do differently? a) Swipe the card more slowly so that the reader has more time to read the magnetic stripe. b) Swipe the card more quickly so that the induced emf is higher. c) Swipe the card more quickly so that the induced currents are reduced. d) Swipe the card more slowly so that the magnetic field don't change so fast. 19) Which of the following travel at the same speed as light? (Choose all that apply) a) Radio waves b) Microwaves c) Radar d) ultrasonic waves e) Infrared radiation g) Gamma rays h) x-rays f) cell phone signals 20) In empty space, which quantity is always larger for x-ray radiation than for a radio wave? a) amplitude b) wavelength c) frequency d) speed 21) An electromagnetic wave is traveling straight down toward the center of the earth. At a certain moment in time the electric field points west. In which direction does the magnetic field point at this moment?