BackThe average intensity of a particular TV station’s signal is 1.0 x 10-13 W/m2 when it arrives at a 33-cm-diameter satellite TV antenna. (a) Calculate the total energy received by the antenna during 3.0 hours of viewing this station’s programs. (b) Estimate the amplitudes of the E and B fields of the EM wave.
What is the average energy contained in a 1.00-m3 volume near the Earth’s surface due to radiant energy from the Sun? See Example 31–6.
You measure the magnetic field strength of a traveling electromagnetic wave to be , oriented along the +x direction. If this EM wave moves in the +y direction, what is the magnitude and direction of the wave's electric field at that same exact spot?
It has been proposed that small spacecraft could reach other planets in a fairly short time—days instead of many months—if they unfurl a reflective sail and are accelerated by a powerful laser beam generated by an earth-orbiting laser. What speed would a spacecraft need to reach Mars in 8.0 days when Mars is closest to earth?
What is the de Broglie wavelength of a 200 g baseball with a speed of 30 m/s?
(I) Electromagnetic waves and sound waves can have the same frequency. (a) What is the wavelength of a 1.00-kHz electromagnetic wave? (b) What is the wavelength of a 1.00-kHz sound wave? (The speed of sound in air is 341 m/s.) (c) Can you hear a 1.00-kHz electromagnetic wave?
Why do some microwave ovens rotate the food container? Suppose the metal walls form a rectangular cavity of dimensions 37 cm x 37 cm x 20 cm. When 2.45-GHz microwaves are continuously introduced into this cavity, reflection of incident waves from the walls sets up standing waves with nodes at the walls. Along the 37-cm dimension of the oven, how many nodes exist (excluding the nodes at the wall) and what is the distance between adjacent nodes? (No heating occurs at these nodes, so rotating the food container gives more even heating of the food.)
(II) (a) Suppose for a conventional X-ray image that the X-ray beam consists of parallel rays. What would be the magnification of the image? (b) Suppose, instead, that the X-rays come from a point source (as in Fig. 35–31) that is 15 cm in front of a human body which is 25 cm thick, and the film is pressed against the person’s back. Determine and discuss the range of magnifications that result.
<IMAGE>
A scientist measures a 3.00-mV rms voltage across a 1.50-m-long sensor that is aligned with the electric field of an electromagnetic wave. What is the electric field strength and the corresponding rate of energy transport per m2?
(II) How much energy is transported across a 1.00-cm² area per hour by an EM wave whose E field has an rms strength of 25.8 mV/m?
What is the quantum number of an electron confined in a 3.0-nm-long one-dimensional box if the electron’s de Broglie wavelength is 1.0 nm?
One way to measure the strength of a magnetic field is with a flip coil. Suppose a 200-turn, 4.0-cm-diameter coil with a resistance of 2.0 Ω is connected to a ballistic galvanometer, a device that measures the total charge passing through. The coil is held perpendicular to the field, then quickly flipped 180° so that the opposite side is facing the magnetic field. Afterward, the galvanometer reads 7.5 μC. What is the field strength? Hint: Use I = dq/dt to relate the net change of flux to the amount of charge that flows through the galvanometer.
(II) How long would it take a message sent as radio waves from Earth to reach Mars when Mars is (a) nearest Earth, (b) farthest from Earth? Assume that Mars and Earth are in the same plane and that their orbits around the Sun are circles (Mars is 230 x 106 km from the Sun).
(I) The field in an EM wave has a peak of 23.5 mV/m. What is the average rate at which this wave carries energy across unit area per unit time?