I electromagnets, the magnetic field is turned off when there is no induced current. So, electromagnets act as magnets only when current is induced in an insulated wire wrapped around a material mage of ferromagnetic material such as iron core rotating in a magnetic field.
So, option D is the correct one.
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The frequency of any wave is (speed) / (wavelength).
Frequency = (330 m/s) / (2m) = 165 per second = <em>165 Hz</em>.
Period = 1 / frequency = 1 / (165 per second) = <em>0.0061 second </em>
Answer: A. Frequency
B. Wavelength
Explanation: Electromagnetic waves are waves which can travel through the vacuum. Electromagnetic waves have electrical and magnetic component associated with them.
Electromagnetic waves are arranged in order of increasing frequencies or decreasing wavelengths.
Radio waves, X-rays, and gamma rays are all electromagnetic waves which have different wavelengths and thus have different frequencies. But they all travel with the speed of light.

The order of frequency of given waves : gamma rays > X rays> Radio waves.
The order of wavelength of given waves : gamma rays < X rays < Radio waves.
Answer:
1. In general, the best shields will be able to block a spectrum of radiation. Aboard the space station, the use of hydrogen-rich shielding such as polyethylene in the most frequently occupied locations, such as the sleeping quarters and the galley, has reduced the crew's exposure to space radiation.
2. It absorbs harmful ultraviolet radiation from the sun, helps keep Earth's surface warm via the greenhouse effect, and reduces temperature extremes between day and night. ... So, thanks to gravity, although some of Earth's atmosphere is escaping to space, most is staying here.
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Answer:
Most earthquakes and volcanoes occur because of the movement of the plates, especially as plates interact at their edges or boundaries.
Explanation: