32. Electromagnetic Waves

(II) Our nearest star (other than the Sun) is 4.2 light-years away. That is, it takes 4.2 years for the light it emits to reach Earth. How far away is it in meters?

A laser beam shines straight up onto a flat, black foil of mass m. Find an expression for the laser power P needed to levitate the foil.

CALC An electric generator has an 18-cm-diameter, 120-turn coil that rotates at 60 Hz in a uniform magnetic field that is perpendicular to the rotation axis. What magnetic field strength is needed to generate a peak voltage of 170 V?

When estimating the distance to lightning, you can time how long after the light flash is seen until the thunder is heard. Sound travels 343 m/s, so a good estimate is to allow 3.0 seconds per kilometer. There is actually a small mistake with this method because the time for the light to travel is not accounted for. How big is this mistake (%) for a lightning flash 2.0 km away?

Which of the following is a key difference between electromagnetic waves and mechanical waves?

Which of the following best describes a key difference between electromagnetic waves and mechanical waves?

Show that displacement current, ε₀ (dΦE/dt), has the SI units of amperes.

In the context of electromagnetic waves, increasing the number of loops in a coil will increase the $magnitude$ of the magnetic field produced by the coil. Which property does this refer to?

(II) A light-year is a measure of distance (not time). How many meters does light travel in a year?

Which of the following best describes a key difference between electromagnetic waves and mechanical waves?

Assume that the nearest stars to us have an intrinsic luminosity about the same as the Sun’s. Their apparent brightness, however, is about 10¹¹ times fainter than the Sun. From this, estimate the distance to the nearest stars.

Estimate how long an AM antenna would have to be if it were (a) ½ ⋋ or (b) ¼ ⋋ AM radio is roughly 1 MHz (530 kHz to 1.7 MHz).

(II) The magnetic field in a traveling EM wave has an rms strength of 22.5 nT. How long does it take to deliver 415 J of energy to 1.00 cm² of a wall that it hits perpendicularly?