Physics-13 The Electromagnetic Spectrum PreQuiz

What is a line of points in phase with each other in a wave, perpendicular to the direction of energy transfer

• wavefront

• diffraction

• microwaves

• radio waves

• pulsars

Answer explanation

波阵面 Awavefront is a line of points in phase with each other in a wave, perpendicular to the direction of energy transfer.

In physics, the wavefront of a time-varying wave field is the set (locus) of all points having the same phase. The term is generally meaningful only for fields that, at each point, vary sinusoidally in time with a single temporal frequency (otherwise the phase is not well defined).

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When a wave spreads out as it travels through a gap or past the edge of an object.

• wavefront

• diffraction

• microwaves

• radio waves

• pulsars

Answer explanation

衍射 Diffraction occurs when an object causes a wave to change direction and bend around it.

Diffraction is the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.

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Electromagnetic waves that have shorter wavelengths and higher frequencies than radio waves.

• wavefront

• diffraction

• microwaves

• radio waves

• pulsars

Answer explanation

微波炉 Electromagnetic waves that have shorter wavelengths and higher frequencies than radio waves.

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This is the part of the electromagnetic spectrum that consists of waves with the lowest frequencies:

• wavefront

• diffraction

• microwaves

• radio waves

• pulsars

Answer explanation

无线电波 the part of the electromagnetic spectrum that consists of waves with the lowest frequencies

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This is a rapidly spinning neutron star that emits pulses of radio and optical energy:

• wavefront

• diffraction

• microwaves

• radio waves

• pulsars

Answer explanation

脉冲星 A pulsar is a rapidly spinning neutron star that emits pulses of radio and optical energy

A pulsar (from pulsating radio source) is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth (similar to the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays. (See also centrifugal mechanism of acceleration.)

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A ______ relays radio, television, and phone signals to receivers on earth

• communication satelite

• Analogue signal

• x-rays

• gamma rays

• digital signal

Answer explanation

通讯卫星 A communication satelite relays radio, television, and phone signals to receivers on earth

A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications.^[1] Many communications satellites are in geostationary orbit 22,300 miles (35,900 km) above the equator, so that the satellite appears stationary at the same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit, where antennas on the ground have to follow the position of the satellites and switch between satellites frequently.

The high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points.^[2] Communications satellites use a wide range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference.^[3]

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This is electromagnetic radiation having a very short wavelength; can penetrate substances such as skin and muscle:

• communication satelite

• Analogue signal

• x-rays

• gamma rays

• digital signal

Answer explanation

X射线 An X-ray is electromagnetic radiation having a very short wavelength; can penetrate substances such as skin and muscle.

X-ray radiation, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 nanometers to 10 picometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×10¹⁶ Hz to 3×10¹⁹ Hz) and energies in the range 124 keV to 145 eV, respectively. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895.^[1] He named it X-radiation to signify an unknown type of radiation.^[2] Spellings of X-ray(s) in English include the variants x-ray(s), xray(s), and X ray(s).^[3

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This is a continuous signal that varies in amplitude or frequency with the information being transmitted:

• communication satelite

• Analogue signal

• x-rays

• gamma rays

• digital signal

Answer explanation

模拟信号 An analogue signal is a continuous signal that varies in amplitude or frequency with the information being transmitted

An analog signal is any continuous-time signal representing some other quantity, i.e., analogous to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies continuously with the pressure of the sound waves.^[1]

In contrast, a digital signal represents the original time-varying quantity as a sampled sequence of quantized values. Digital sampling imposes some bandwidth and dynamic range constraints on the representation and adds quantization error.^[2]

The term analog signal usually refers to electrical signals; however, mechanical, pneumatic, hydraulic, and other systems may also convey or be considered analog signals.

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This is a signal that consists of a series of pulses which are either on or off:

• communication satelite

• Analogue signal

• x-rays

• gamma rays

• digital signal

Answer explanation

数字信号 A digital signal is a signal that consists of a series of pulses which are either on or off.

A digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values.^[1][2][3] This contrasts with an analog signal, which represents continuous values; at any given time it represents a real number within a continuous range of values.

Simple digital signals represent information in discrete bands of analog levels. All levels within a band of values represent the same information state. In most digital circuits, the signal can have two possible valid values; this is called a binary signal or logic signal.^[4] They are represented by two voltage bands: one near a reference value (typically termed as ground or zero volts), and the other a value near the supply voltage. These correspond to the two values "zero" and "one" (or "false" and "true") of the Boolean domain, so at any given time a binary signal represents one binary digit (bit). Because of this discretization, relatively small changes to the analog signal levels do not leave the discrete envelope, and as a result are ignored by signal state sensing circuitry. As a result, digital signals have noise immunity; electronic noise, provided it is not too great, will not affect digital circuits, whereas noise always degrades the operation of analog signals to some degree.^[5]

This is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei:

• communication satelite

• Analogue signal

• x-rays

• gamma rays

• digital signal

Answer explanation

伽马射线 A Gamma Ray is a penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei.

A gamma ray, also known as gamma radiation (symbol γ or �), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically shorter than those of X-rays. With frequencies above 30 exahertz (3×10¹⁹ Hz), it imparts the highest photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter; in 1900 he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel) alpha rays and beta rays in ascending order of penetrating power.

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