301. Use the graph description below. The horizontal axis is electromagnetic spectrum position from radio waves at the left to gamma rays at the right. A curve labelled "typical photon energy" rises steadily from left to right. The best interpretation is that
ⓐ. photon energy decreases as frequency increases across the spectrum
ⓑ. photon energy increases as frequency increases across the spectrum
ⓒ. all spectrum regions have the same photon energy because speed is common
ⓓ. radio waves have the greatest photon energy because their wavelength is longest
Correct Answer: photon energy increases as frequency increases across the spectrum
Explanation: Moving from radio waves to gamma rays means moving toward higher frequency. The photon energy relation \(E=h\nu\) shows that energy is directly proportional to frequency. Therefore, the rising curve is consistent with increasing photon energy from left to right. The common vacuum speed \(c\) does not make photon energies equal. The longest wavelengths belong to the lowest-frequency, lowest-photon-energy end of the spectrum.
302. Read the situation below and answer the question.
A scientist chooses radiation for four tasks: long-distance broadcasting, thermal imaging of a warm surface, viewing a bone fracture, and sterilising packaged medical tools.
The most suitable order of radiation types for these tasks is
ⓐ. gamma rays, radio waves, infrared, visible light
ⓑ. infrared, microwaves, radio waves, ultraviolet
ⓒ. X-rays, visible light, microwaves, radio waves
ⓓ. radio waves, infrared, X-rays, gamma rays
Correct Answer: radio waves, infrared, X-rays, gamma rays
Explanation: Long-distance broadcasting is commonly associated with radio waves. Thermal imaging detects infrared radiation emitted by warm surfaces. Viewing a bone fracture commonly uses X-rays because they penetrate soft tissue more than bone. Sterilising packaged medical tools can use gamma rays because of their penetrating and ionising nature. The order in the answer follows the tasks in the passage, not the full frequency order of the spectrum.
303. A table compares four electromagnetic regions for source, effect, and use.
| Region | Typical source or interaction | Common use or effect |
|---|
| P. Radio waves | Oscillating charges in antennas | Broadcasting and communication |
| Q. Infrared | Emission from warm bodies | Thermal imaging |
| R. X-rays | Fast electrons suddenly stopped | Medical imaging |
| S. Gamma rays | Nuclear transitions | Sterilisation or cancer therapy |
The best judgement about the table is that
ⓐ. all four rows are physically suitable
ⓑ. only P and Q are suitable
ⓒ. only R and S are suitable
ⓓ. all rows are wrong because uses cannot identify spectrum regions
Correct Answer: all four rows are physically suitable
Explanation: Row P correctly links radio waves with antennas and communication. Row Q correctly connects infrared radiation with warm-body emission and thermal imaging. Row R correctly links X-rays with sudden stopping of fast electrons and medical imaging. Row S correctly connects gamma rays with nuclear transitions and high-energy applications such as sterilisation or cancer therapy. The table is not using applications alone; it combines source, interaction, and use to identify each region.
304. The atmosphere does not transmit all electromagnetic waves equally. This means that
ⓐ. every wavelength is absorbed by the atmosphere in exactly the same way
ⓑ. only visible light can pass through the atmosphere
ⓒ. atmospheric transparency depends on radiation wavelength or frequency
ⓓ. electromagnetic waves become longitudinal inside air
Correct Answer: atmospheric transparency depends on radiation wavelength or frequency
Explanation: The atmosphere is not equally transparent to every part of the electromagnetic spectrum. Some wavelength ranges pass through fairly well, while other ranges are strongly absorbed or scattered. Visible light reaches Earth's surface efficiently through a useful atmospheric window. Some radio waves also travel well through the atmosphere and are used for communication. The statement is about selective transmission and absorption, not about changing the basic transverse nature of electromagnetic waves.
305. Visible light reaches Earth's surface in large amount because the atmosphere has
ⓐ. complete opacity to all wavelengths near visible light
ⓑ. a visible window of relatively good transparency
ⓒ. no interaction with any electromagnetic wave
ⓓ. a rule that only gamma rays can pass through it
Correct Answer: a visible window of relatively good transparency
Explanation: A visible atmospheric window means that the atmosphere transmits much of the visible part of the electromagnetic spectrum. This is why sunlight in the visible range can illuminate Earth's surface. Other parts of the spectrum may be absorbed more strongly by atmospheric gases. The word "window" does not mean there is a physical opening in the atmosphere. It means a wavelength range where transmission is comparatively high.
306. A radio signal from a distant transmitter is received clearly over a large region. One suitable atmospheric reason is that
ⓐ. some radio bands propagate through atmospheric windows
ⓑ. radio waves are not electromagnetic radiation
ⓒ. radio waves always have higher frequency than gamma rays
ⓓ. all radio waves are completely absorbed by the ozone layer
Correct Answer: some radio bands propagate through atmospheric windows
Explanation: Radio waves are electromagnetic waves with relatively low frequencies and long wavelengths. Some radio-frequency ranges can travel through the atmosphere effectively, making them useful for communication. In some cases, interaction with the ionosphere also affects long-distance propagation. This does not mean every radio wave behaves identically under all atmospheric conditions. The useful idea is that propagation depends on frequency band and atmospheric conditions.
307. Read the situation below and answer the question.
A communication engineer chooses microwave frequencies for a satellite link. The signal must pass through a large part of the atmosphere before reaching the receiver.
The choice is reasonable mainly because
ⓐ. selected microwave bands can carry signals through air
ⓑ. microwaves are sound waves that need air for travel
ⓒ. microwaves have lower frequency than all radio waves
ⓓ. microwaves are completely absorbed by every gas in air
Correct Answer: selected microwave bands can carry signals through air
Explanation: Microwaves are electromagnetic waves and can carry communication signals. Suitable microwave bands are used in satellite communication because they can pass through the atmosphere reasonably well under chosen conditions. Their shorter wavelengths also allow directional transmission using antennas and dishes. They are not sound waves, so they do not require air as a mechanical medium. The phrase "suitable bands" matters because atmospheric absorption depends on the exact frequency and path conditions.
308. Ozone in the upper atmosphere is important because it absorbs much of the harmful part of
ⓐ. radio waves
ⓑ. microwaves
ⓒ. infrared radiation from remote controls only
ⓓ. ultraviolet radiation
Correct Answer: ultraviolet radiation
Explanation: Ozone absorbs a significant part of harmful ultraviolet radiation from the Sun. This reduces the amount of damaging high-frequency ultraviolet radiation reaching Earth's surface. Radio waves and microwaves are not the main radiation for which the ozone layer is known as a protective absorber. Infrared radiation is mainly associated with heat and molecular absorption by other atmospheric gases. The ozone example shows that atmospheric absorption can be beneficial for life.
309. A claim says, "If ozone absorbs ultraviolet radiation, then no ultraviolet radiation can ever reach Earth's surface." The claim is
ⓐ. valid because ozone blocks all ultraviolet frequencies perfectly
ⓑ. valid because ultraviolet is not electromagnetic radiation
ⓒ. invalid because ozone absorbs only radio-frequency waves
ⓓ. invalid because ozone absorbs harmful UV but not all UV
Correct Answer: invalid because ozone absorbs harmful UV but not all UV
Explanation: Ozone is an important absorber of harmful ultraviolet radiation. However, saying that no ultraviolet radiation reaches Earth's surface is too absolute. Different ultraviolet ranges are absorbed to different extents, and some ultraviolet radiation can still reach the lower atmosphere and surface. The protective role of ozone is therefore strong but not a perfect all-wavelength shield. This is why ultraviolet exposure and sunburn can still occur even with ozone present.
310. Some gases in the atmosphere absorb infrared radiation emitted by Earth's surface. This absorption is connected with
ⓐ. production of X-rays by metal targets
ⓑ. radio broadcasting by antennas
ⓒ. greenhouse-related heating of the lower atmosphere
ⓓ. direct conversion of infrared radiation into nuclear gamma rays
Correct Answer: greenhouse-related heating of the lower atmosphere
Explanation: Earth's surface emits infrared radiation because it is warm. Some atmospheric gases absorb part of this infrared radiation and re-emit energy, contributing to warming of the lower atmosphere. This is the greenhouse-related context for infrared absorption. The process is not X-ray production, because X-rays involve much higher-frequency radiation and different sources. Infrared absorption depends on molecular interactions, not on nuclear transitions.
311. Study the table and select the row that gives a suitable atmospheric interaction.
| Row | Radiation region | Atmospheric context |
|---|
| P | Ultraviolet | Much harmful ultraviolet is absorbed by ozone |
| Q | Infrared | No atmospheric gas can absorb it under any condition |
| R | Microwaves | Never used for satellite communication |
| S | Visible light | Completely blocked by the atmosphere at all times |
ⓐ. Row Q
ⓑ. Row R
ⓒ. Row P
ⓓ. Row S
Correct Answer: Row P
Explanation: Ozone absorbs much harmful ultraviolet radiation, so row P gives a suitable atmospheric interaction. Infrared radiation can be absorbed by some atmospheric molecules, so row Q is too absolute. Microwaves are used in satellite communication in suitable frequency bands, so row R is wrong. Visible light can reach Earth's surface through a relatively transparent atmospheric window, so row S is also unsuitable. The correct comparison depends on selective absorption rather than one rule for all electromagnetic waves.
312. Consider the following statements about atmospheric propagation.
Statement I: The atmosphere has wavelength ranges through which radiation passes more easily.
Statement II: Ozone absorbs much harmful ultraviolet radiation.
Statement III: Infrared absorption by atmospheric molecules has no heating relevance.
ⓐ. II and III only
ⓑ. I and II only
ⓒ. I and III only
ⓓ. I, II and III
Correct Answer: I and II only
Explanation: Statement I is true because atmospheric transmission varies with wavelength, forming useful windows. Statement II is true because ozone absorbs much harmful ultraviolet radiation. Statement III is false because infrared absorption by atmospheric molecules is directly connected with greenhouse-related heating. The atmosphere can transmit some parts of the spectrum while absorbing others. This selective behaviour is why different electromagnetic regions have different practical roles in communication, observation, and climate context.
313. Use the graph description below. The horizontal axis represents electromagnetic wavelength. A labelled band near visible wavelengths has high transmission, a labelled ultraviolet band has low transmission due to ozone absorption, and some infrared bands have reduced transmission due to molecular absorption. The graph mainly shows that
ⓐ. atmospheric transmission is selective across the spectrum
ⓑ. all electromagnetic waves have identical absorption in air
ⓒ. visible light is not part of the electromagnetic spectrum
ⓓ. infrared radiation has higher frequency than ultraviolet
Correct Answer: atmospheric transmission is selective across the spectrum
Explanation: The graph description compares transmission in different wavelength bands. High transmission near visible wavelengths suggests an atmospheric window. Low transmission in part of the ultraviolet range is linked with ozone absorption. Reduced infrared transmission is linked with absorption by atmospheric molecules. The graph therefore shows selective atmospheric transparency, not a single absorption value for all electromagnetic waves.
314. A satellite link and a ground-based thermal camera use different atmospheric conditions. The satellite link commonly uses selected microwave bands, while the thermal camera detects infrared radiation from warm objects. The correct interpretation is that
ⓐ. both uses depend only on the visible-light atmospheric window
ⓑ. infrared radiation cannot be emitted by warm bodies
ⓒ. microwaves and infrared are outside the electromagnetic spectrum
ⓓ. microwaves and infrared use different atmospheric interactions
Correct Answer: microwaves and infrared use different atmospheric interactions
Explanation: Microwave communication uses electromagnetic waves in selected frequency bands that can be transmitted and received efficiently for communication. Infrared detection uses radiation emitted by warm objects. The atmosphere may transmit or absorb different infrared and microwave ranges differently. These two applications therefore rely on different spectrum regions and different practical interactions. They are both electromagnetic waves, but their sources, uses, and atmospheric behaviour are not identical.
315. Electromagnetic radiation is called ionising when it has enough photon energy to
ⓐ. travel at a speed greater than \(c\) in vacuum
ⓑ. remove electrons from atoms or molecules
ⓒ. become a sound wave in air
ⓓ. lose its electric and magnetic fields
Correct Answer: remove electrons from atoms or molecules
Explanation: Ionising radiation has photons energetic enough to remove electrons from atoms or molecules. This can produce ions and can cause chemical or biological effects. High-frequency electromagnetic waves such as X-rays and gamma rays are strongly associated with ionising behaviour. Lower-frequency waves such as radio waves, microwaves, and infrared generally do not ionise matter by individual photon energy. The distinction is based on photon energy, not on vacuum speed.
316. Among the following, the pair most strongly associated with ionising electromagnetic radiation is
ⓐ. radio waves and microwaves
ⓑ. infrared and radio waves
ⓒ. microwaves and visible red light
ⓓ. X-rays and gamma rays
Correct Answer: X-rays and gamma rays
Explanation: X-rays and gamma rays have very high frequencies and high photon energies. This makes them strongly associated with ionising effects. Radio waves, microwaves, and infrared radiation generally have much lower photon energies. They can still transfer energy and cause heating at sufficient intensity, but that is not the same as ionisation by individual photons. The ionising classification therefore follows the high-frequency end of the electromagnetic spectrum.
317. A microwave oven heats food, but microwaves are not usually described as ionising radiation. The best explanation is that microwaves
ⓐ. heat mainly by energy transfer to polar molecules
ⓑ. ionise atoms easily because their photon energy is high
ⓒ. are low-intensity gamma rays rather than microwaves
ⓓ. do not transfer any energy to the food
Correct Answer: heat mainly by energy transfer to polar molecules
Explanation: Microwaves carry energy and can heat food effectively. In a microwave oven, the alternating electric field interacts strongly with polar molecules such as water. This transfers energy into molecular motion and heating. The photon energy of microwaves is far lower than that of X-rays or gamma rays, so ordinary microwave heating is not ionisation by individual photons. Heating and ionisation are different physical effects, even though both involve energy transfer.
318. A claim says, "All electromagnetic waves are dangerous in the same way because they all carry energy." The claim is
ⓐ. correct because any energy transfer must produce ionisation
ⓑ. correct because radio waves and gamma rays have the same photon energy
ⓒ. incorrect because effects depend on energy, intensity and exposure
ⓓ. incorrect because electromagnetic waves carry no energy
Correct Answer: incorrect because effects depend on energy, intensity and exposure
Explanation: All electromagnetic waves can carry energy, but their effects on matter are not identical. X-rays and gamma rays have high photon energies and can be ionising. Radio waves, microwaves, and infrared radiation generally have lower photon energies and are more commonly associated with induced currents or heating effects when strong enough. The intensity, duration of exposure, and how matter absorbs the radiation also matter. Equal vacuum speed does not mean equal biological effect.
319. Study the safety classification table and choose the most suitable row.
| Row | Radiation | Typical safety description |
|---|
| P | Gamma rays | High-energy ionising radiation requiring shielding and dose control |
| Q | Radio waves | Always more ionising than X-rays |
| R | Infrared | Unable to heat matter under any condition |
| S | Microwaves | Ionising mainly because they have the shortest wavelength in the spectrum |
ⓐ. Row Q
ⓑ. Row P
ⓒ. Row R
ⓓ. Row S
Correct Answer: Row P
Explanation: Gamma rays are high-frequency, high-energy electromagnetic radiation and are strongly ionising. Because they can penetrate matter and affect living tissue, shielding and dose control are important. Radio waves are much lower in photon energy than X-rays, so row Q reverses the safety comparison. Infrared radiation can heat matter, so row R is too absolute. Microwaves do not have the shortest wavelength in the spectrum, and their ordinary heating action is not mainly ionisation.
320. Assertion: X-rays require careful use in medical imaging.
Reason: X-rays are ionising electromagnetic radiation and can interact strongly with matter.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Assertion is true, but Reason is false
ⓒ. Both Assertion and Reason are true, and Reason explains Assertion
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: X-rays are useful in medical imaging because they penetrate soft tissue and are absorbed differently by denser materials such as bone. They are also ionising, so unnecessary exposure must be avoided. The Reason explains why careful use is required: ionising radiation can affect matter and living tissue. Controlled exposure allows useful imaging while reducing unwanted risk. The usefulness of X-rays and the need for care come from the same high-frequency nature.
