Electricity and Magnetism Answers

(a) Two microwave frequencies are authorized for use in microwave ovens: 900 and 2560 MHz. Calculate the wavelength of each.

(b) Which frequency would produce smaller hot spots in foods due to interference effects?

The maximum magnetic field strength of an electromagnetic field is 5×10⁻⁶T. Calculate the maximum electric field strength if the wave is traveling in a medium in which the speed of the wave is 0.75c

Show that, when SI units for μ0 and ϵ0 are entered, the units given by the right-hand side of the equation in the problem above are m/s.

Show that, when SI units for μ0 and ϵ0 are entered, the units given by the right-hand side of the equation in the problem above are m/s.

The energy stored per unit volume of the inductor is called the energy density of the magnetic field. Why?

A solid copper sphere has a net positive charge. The charge is distributed uniformly over the surface of the sphere, and the electric field inside the sphere is zero. Then a negative point charge outside the sphere is brought close to the surface of the sphere. Is all the net charge on the sphere still on its surface? If so, is this charge still distributed uniformly over the surface? If it is not uniform, how is it distributed? Is the electric field inside the sphere still zero? In each case justify your answers.

A certain region of space bounded by an imaginary closed surface contains no charge. Is the electric field always zero everywhere on the surface? If not, under what circumstances is it zero on the surface?

The air temperature and the velocity of the air have different values at different places in the earth’s atmosphere. Is the air velocity a vector field? Why or why not? Is the air temperature a vector field? Again, why or why not? 

Two identical metal objects are mounted on insulating stands. Describe how you could place charges of opposite sign but exactly equal magnitude on the two objects.

Sufficiently strong electric fields can cause atoms to become positively ionized—that is, to lose one or more electrons. Explain how this can happen. What determines how strong the field must be to make this happen?