How is an electromagnet different from a bar magnet?
a) only a bar magnet has a magnetic field.
b) only an electromagnet attracts materials made of iron.
c) an electromagnet is temporary and is magnetic when a current flows through a wire wrapped around the core.
d) a bar magnet is a temporary and is only magnetic when a current flows through a wire wrapped around the core.

What is the average speed of a car that travels 40 mph for 1 hour and 60 mph in another hour?

Frequency of electromagnetic waves that a radio station is assigned is called

Acertain sound is recorded by a microphone. the same microphone then detects a second sound, which is identical to the first one except that the amplitude of the pressure fluctuations is larger. in addition to the larger amplitude, what distinguishes the second sound from the first one? it is perceived as higher in pitch. it is perceived as louder. it has a higher frequency. it has a longer wavelength.